Date: 18 Aug 2004 19:40:45 +0200
From: SecuriTeam <[email protected]>
To: [email protected]Subject: [UNIX] Courier-IMAP Remote Format String Vulnerability
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Courier-IMAP Remote Format String Vulnerability
------------------------------------------------------------------------
SUMMARY
<http://www.courier-mta.org/imap/>; Courier-IMAP is "an IMAP/POP3 mail
server popular on sites utilizing Qmail/Exim/Postfix". Remote exploitation
of a format string vulnerability in Double Precision Inc.'s, Courier-IMAP
daemon allows attackers to execute arbitrary code.
DETAILS
Vulnerable Systems:
* Courier-IMAP versions 1.6.0 up to 2.2.1
Immune Systems:
* Courier-IMAP version 3.0.7
The vulnerability specifically exists within the auth_debug() function
defined in authlib/debug.c:
void auth_debug( const char *fmt, va_list ap ) {
char buf[DEBUG_MESSAGE_SIZE];
int i;
int len;
// print into buffer to be able to replace control and other
// unwanted chars.
vsnprintf( buf, DEBUG_MESSAGE_SIZE, fmt, ap );
len = strlen( buf );
// replace nonprintable chars by dot
for( i=0 ; i<len ; i++ )
if( !isprint(buf[i]) )
buf[i] = '.';
// emit it
fprintf( stderr, buf ); // <- Format String Vulnerability
fprintf( stderr, "\n" );
}
The 'buf' variable utilized in the fprintf() call is attacker-controlled
and can contain format string modifiers allowing an attacker to manipulate
the stack and eventually execute arbitrary code.
Analysis:
Successful exploitation does not require authentication thereby allowing
any remote attacker to execute arbitrary code under the privileges of the
user that the IMAP daemon runs as. The vulnerable function auth_debug() is
only called if login debugging is enabled requiring that the 'DEBUG_LOGIN'
be set to either '1' or '2' in the imapd configuration file.
Workaround:
Disable the login debugging option of Courier-IMAP. This can be
accomplished by setting 'DEBUG_LOGIN' to '0' in the configuration file
usually located at /usr/lib/courier-imap/etc/imapd.
Vendor response:
This issue has been resolved in the latest version of Courier IMAP
(v3.0.7). As well, the default setting of 'DEBUG_LOGIN' is '0'.
CVE Information:
<http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2004-0777>;
CAN-2004-0777
Disclosure timeline:
08/10/2004 Initial vendor contact
08/10/2004 iDEFENSE clients notified
08/11/2004 Initial vendor response
08/18/2004 Public disclosure
ADDITIONAL INFORMATION
The information has been provided by
<mailto:[email protected]> iDEFENSE.
The original article can be found at:
<http://www.idefense.com/application/poi/display?id=131&type=vulnerabilities&flashstatus=true>; http://www.idefense.com/application/poi/display?id=131&type=vulnerabilities&flashstatus=true
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