Please use GitHub private vulnerability reporting. Do not open a public issue for a suspected vulnerability.

Include the action commit, runner operating system, relevant inputs, toolchain file, and a minimal reproduction. Do not include credentials or private repository data.

Security fixes are applied to the current major action line. Consumers should pin a reviewed full commit SHA and update that pin after a fix is released.

Inputs and repository paths are treated as untrusted data. The action validates rustup names and its supported toolchain-file subset, rejects working directories outside GITHUB_WORKSPACE, invokes commands without a shell, and stops when no explicit input or repository toolchain file selects Rust. The selected channel is forced through RUSTUP_TOOLCHAIN, so persistent rustup directory overrides cannot replace repository policy.

Local path and linked custom toolchains are deliberately unsupported. The action disables rustup self-update and restores an initially absent global default after installation.

The action trusts the selected action commit, the runner, the installed rustup executable, and rustup's configured distribution server. It does not verify the Rust distribution independently and does not protect a workflow from a compromised self-hosted runner or a malicious workflow author.