Squid is a caching proxy for the Web. Due to an Uncontrolled Recursion bug in versions 2.6 through 2.7.STABLE9, versions 3.1 through 5.9, and versions 6.0.1 through 6.5, Squid may be vulnerable to a Denial of Service attack against HTTP Request parsing. This problem allows a remote client to perform Denial of Service attack by sending a large X-Forwarded-For header when the follow_x_forwarded_for feature is configured. This bug is fixed by Squid version 6.6. In addition, patches addressing this problem for the stable releases can be found in Squid's patch archives.
Exploitability
AV:NAC:LPR:NUI:NScope
S:CImpact
C:NI:NA:H8.6/CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:HOther