CVE-2026-47729

Red Hat statement

To exploit this issue, an attacker must have a valid account on the Squid proxy and must also control an FTP server reachable from the proxy on port 21. HTTPS traffic handled via CONNECT tunnels (the vast majority of modern web traffic) is opaque to the proxy because the underlying request data is encrypted and Squid does not have access to it. The impact is limited to information disclosure of cleartext HTTP request contents or traffic in TLS-terminating (SSL bump) proxy configurations where Squid decrypts and inspects traffic. FTP protocol usage has declined considerably in most environments since major browsers removed FTP support, further narrowing the practical attack surface. Due to these reasons, this vulnerability has been rated with a moderate severity.

Red Hat mitigation

When FTP access is not required, block FTP traffic at the proxy by adding the following settings to the squid.conf configuration file above any custom 'http_access allow' rules: ~~~ acl FTP proto FTP http_access deny FTP ~~~ When FTP access is required, configure Squid to only allow FTP access to specific and trusted destination domains. See the example below for restricting FTP access to the 'trusted.server.example.com' domain: ~~~ acl FTP proto FTP acl ftp_allowlist dstdomain .trusted.server.example.com http_access deny FTP !ftp_allowlist ~~~