Squid is a caching proxy for the Web. Prior to 7.6, due to an improper input validation bug in cache digest reply handling (peerDigestSwapInMask in src/peerdigest.cc), Squid is vulnerable to a heap-based buffer overflow: a cache digest's on-the-wire size may be larger than the masksize declared within the digest, so a trusted peer sending a maliciously crafted reply to a cachedigest request message can trigger the overflow. This attack is limited to Squid instances compiled with the --enable-cache-digests option and configured with cachepeer entries. This issue is fixed in version 7.6.