Public Vulnerability Reports

Squid Web Proxy Cache NTLM Authentication Helper Buffer Overflow Vulnerability



Squid is a fully-featured Web Proxy Cache designed to run on Unix
systems and supports proxying and caching of HTTP, FTP, and other URLs,
as well as SSL support, cache hierarchies, transparent caching, access
control lists and many other features. More information is available at


Remote exploitation of a buffer overflow vulnerability in Squid Web
Proxy Cache could allow a remote attacker to execute arbitrary code.
Squid Web Proxy Cache supports Basic, Digest and NTLM authentication.
The vulnerability specifically exists within the NTLM authentication
helper routine, ntlm_check_auth(), located in

char *ntlm_check_auth(ntlm_authenticate * auth, int auth_length)
    int rv;
    char pass[25] /*, encrypted_pass[40] */;
    char *domain = credentials;
    memcpy(pass, tmp.str, tmp.l);

The function contains a buffer overflow vulnerability due to a lack of
bounds checking on the values copied to the 'pass' variable. Both the
'tmp.str' and 'tmp.l' variables used in the memcpy() call contain
user-supplied data.


A remote attacker can compromise a target system if Squid Proxy is
configured to use the NTLM authentication helper. The attacker can send
an overly long password to overflow the buffer and execute arbitrary


iDEFENSE has confirmed the existence of this vulnerability in
Squid-Proxy 2.5.*-STABLE and 3.*-PRE when Squid-Proxy is compiled with
the NTLM helper enabled.



Recompile Squid-Proxy with NTLM handlers disabled.


A patch for this issue is available at:


The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CAN-2004-0541 to this issue. This is a candidate for inclusion in
the CVE list (, which standardizes names for
security problems.


04/27/2004   Exploit acquired by iDEFENSE
05/19/2004   iDEFENSE Clients notified
05/20/2004   Initial vendor notification
05/20/2004   Initial vendor response
06/07/2004   Public Disclosure


The discoverer wishes to remain anonymous.

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Copyright © 2004 Verisign, Inc.

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