GHSA-39g5-644c-qwcg: container: pf Rule Injection via Domain Name Argument in `container system dns create --localhost` Command

The container system dns create --localhost command accepts a domainName argument and passes it unsanitized into the pf anchor file (/etc/pf.anchors/com.apple.container) as a comment in a rule line. A domain name containing a newline character breaks out of the comment context and injects an arbitrary pf rule into the anchor file. When pfctl -f subsequently loads the configuration, the attacker-controlled rule is loaded into the macOS kernel packet filter.

A isValidDomainName() function exists in Parser.swift:892 but is never called from DNSCreate.

The core harm caused by this vulnerability is the bypassing of sudo privileges. An administrator may have only granted a user or an automation tool such as CI/CD the ability to execute container system dns create with root privileges, expecting that the user or automation tool could only add redirects from other IPs to localhost in the firewall rules file via --localhost. However, an attacker can exploit this vulnerability to write arbitrary rules into the firewall rules file: the target address is no longer restricted to localhost, and the rules are no longer limited to redirects.