Squid 3.2 < 3.5.4 Incorrect X509 Server Certificate Validation Vulnerability
Medium Nessus Plugin ID 83529
SynopsisThe remote proxy server may be affected by a certificate validation vulnerability.
DescriptionAccording to its banner, the version of Squid running on the remote host is 3.2 prior to 3.2.14 / 3.3.14 / 3.4.13 / 3.5.4. It is, therefore, potentially affected by a flaw related to certificate validation due to the server hostname not being verified as matching a the domain name in the certificate Subject's Common Name (CN) or the SubjectAltName fields. A man-in-the-middle attacker, using a crafted certificate, can utilize this to spoof a TLS/SSL server, thus allowing the disclosure or manipulation of intercepted data. Note that this flaw is exploitable only if Squid is configured to perform SSL Bumping with the 'client-first' or 'bump' mode of operation.
Note that Nessus has not tested for this issue but has instead relied only on the application's self-reported version number. The patch released to address the issue does not update the version in the banner. If the patch has been applied properly, and the service has been restarted, consider this to be a false positive.
SolutionUpgrade to Squid versions 3.2.14 / 3.3.14 / 3.4.13 / 3.5.4, or apply the vendor-supplied patch.