The Squid Software Foundation Squid HTTP Caching Proxy version prior to version 4.0.23 contains a NULL Pointer Dereference vulnerability in HTTP Response X-Forwarded-For header processing that can result in Denial of Service to all clients of the proxy. This attack appear to be exploitable via Remote HTTP server responding with an X-Forwarded-For header to certain types of HTTP request. This vulnerability appears to have been fixed in 4.0.23 and later.

Incorrect HTTP Request header comparison in Squid HTTP Proxy 3.5.0.1 through 3.5.22, and 4.0.1 through 4.0.16 results in Collapsed Forwarding feature mistakenly identifying some private responses as being suitable for delivery to multiple clients.

Incorrect processing of responses to If-None-Modified HTTP conditional requests in Squid HTTP Proxy 3.1.10 through 3.1.23, 3.2.0.3 through 3.5.22, and 4.0.1 through 4.0.16 leads to client-specific Cookie data being leaked to other clients. Attack requests can easily be crafted by a client to probe a cache for this information.

client_side_request.cc in Squid 3.x before 3.5.18 and 4.x before 4.0.10 allows remote servers to cause a denial of service (crash) via crafted Edge Side Includes (ESI) responses.

Double free vulnerability in Esi.cc in Squid 3.x before 3.5.18 and 4.x before 4.0.10 allows remote servers to cause a denial of service (crash) via a crafted Edge Side Includes (ESI) response.

mime_header.cc in Squid before 3.5.18 allows remote attackers to bypass intended same-origin restrictions and possibly conduct cache-poisoning attacks via a crafted HTTP Host header, aka a "header smuggling" issue.

client_side.cc in Squid before 3.5.18 and 4.x before 4.0.10 does not properly ignore the Host header when absolute-URI is provided, which allows remote attackers to conduct cache-poisoning attacks via an HTTP request.

Squid 3.x before 3.5.17 and 4.x before 4.0.9 allow remote attackers to obtain sensitive stack layout information via crafted Edge Side Includes (ESI) responses, related to incorrect use of assert and compiler optimization.

Buffer overflow in cachemgr.cgi in Squid 2.x, 3.x before 3.5.17, and 4.x before 4.0.9 might allow remote attackers to cause a denial of service or execute arbitrary code by seeding manager reports with crafted data.

Multiple stack-based buffer overflows in Squid 3.x before 3.5.17 and 4.x before 4.0.9 allow remote HTTP servers to cause a denial of service or execute arbitrary code via crafted Edge Side Includes (ESI) responses.