29-Year-Old Squid Proxy Bug 'Squidbleed' Can Leak Cleartext HTTP Requests
Jun 22, 2026
Vulnerability / Server Security
A heap over-read in the Squid web proxy can leak another user's cleartext HTTP request, including any credentials or session tokens it carries, to anyone already allowed to send traffic through the same proxy. The bug traces to a 1997 FTP-parsing change and is still live in Squid's default configuration. Researchers at Calif.io disclosed it in June and named it Squidbleed ( CVE-2026-47729 ), after Heartbleed, which leaked memory the same way. Squid describes this as an attack by a trusted client : someone already permitted to use the proxy, not any random host on the internet. That matches Squid's usual home, shared networks like schools, offices, and public Wi-Fi. In those setups, the attacker is just another user of the same proxy. The leak also only reaches traffic that Squid can read. Normal HTTPS rides an opaque CONNECT tunnel, so Squid never sees inside it; the exposed traffic is cleartext HTTP, plus TLS-terminating setups where Squid decrypts and inspect...
