Due to incorrect buffer management ext_lm_group_acl is vulnerable to a denial of service attack when processing NTLM Authentication credentials. This problem is limited to installations using the
ext_lm_group_acl binary.
Squid 2.x -> 2.7.STABLE9
Squid 3.x -> 3.5.28
Squid 4.x -> 4.9
Due to incorrect input validation the NTLM authentication credentials parser in ext_lm_group_acl may write to memory outside the credentials buffer. On systems with memory access protections this can result in the helper process being terminated unexpectedly. Resulting in the Squid process also terminating and a denial of service for all clients using the proxy.
Advisory : http://www.squid-cache.org/Advisories/SQUID-2020_3.txt
An official patch is available from the Squid archives for both Squid 3.5 and Squid 4.
2019-11-11 : I reported the issue
2019-11-18 : I made a PR on GitHub with a fix
2019-11-22 : Fix was merged
See ‘Severity’ section of report.