ZIX is an independent implementation of the Nix expression language. It parses untrusted input (Nix expressions) and can execute build scripts, so security matters.

Only the latest commit on main is supported. ZIX has not shipped a 1.0 release yet; security fixes land on main and are noted in CHANGELOG.md.

Do not open a public issue for security vulnerabilities. Instead, email the maintainers at the address listed on the GitHub profile, or — if you prefer — open a private advisory via GitHub Security Advisories.

Please include:

• a description of the issue and its impact,
• the affected version/commit,
• a minimal reproduction (an expression or builder invocation),
• any suggested fix, if you have one.

We aim to acknowledge reports within 3 business days and to respond with a plan within 10 business days.

• Memory-safety violations (use-after-free, out-of-bounds, stack overflow from untrusted input) in the lexer, parser, evaluator, NAR codec or builder launcher.
• Sandbox escapes: a zix build --sandbox builder reading or writing outside its permitted paths, or reaching the network.
• Store-path collision or hash-verification bypass in fixed-output/content-addressed derivations.
• Denial of service via pathological input (unbounded recursion, resource exhaustion) that is not handled gracefully.

The sandbox relies on bubblewrap and requires the privileges bubblewrap needs (user namespaces). Without a privileged setup, zix build runs builders unsandboxed by default — treat unsandboxed builds of untrusted derivations as untrusted code execution.

We appreciate responsible disclosure.