GoKawiilA 29-year-old bug in the Squid web proxy, dubbed Squidbleed and tracked as CVE-2026-47729, can let an authorized proxy user retrieve fragments of another user's cleartext HTTP requests, including credentials and session tokens. The security researcher who reported the flaw credited Anthropic's Claude Mythos Preview for the discovery. The Hacker News reports: 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 inspects. The attacker also needs the proxy to reach an FTP server they control on port 21. Both FTP and that port are on by default. [...] If you patch, verify the fix, not just the version. Confirm the guard is in FtpGateway.cc, or check your distribution's backport, since distros ship their own builds (Debian packages Squid 5.7). The public thread is still inconsistent: maintainer Amos Jeffries first said Squid 7.6 carried the fix, then corrected that to 7.7, and on June 22 Debian's Salvatore Bonaccorso noted the referenced commit looks like it is already in 7.6. The fix is small, a null-terminator check before the vulnerable strchr calls, merged to the development branch in April and v7 in May. Squid 7.6 does separately patch CVE-2026-50012, an unrelated cache_digest heap overflow. The cleaner move is the one the researchers recommend anyway: turn FTP off. Chromium dropped FTP years ago, and most networks carry almost none of it, so disabling it removes this attack surface for free, whatever build you run. The risk is real but bounded. SUSE rates it moderate, CVSS 6.5, and the vector explains the score: the attacker needs proxy access (low privileges), and the only impact is confidentiality, nothing on integrity or availability.
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