{"id":"GHSA-8p3x-q3q3-q3v5","aliases":["RUSTSEC-2026-0418"],"status":"published","title":"libz-sys build script leaks environment variables in the build directory","description":"The build script of `libz-sys` version \u003c= 1.1.30 prints the full environment\nof the build, including any secrets it contains, to its stdout when compiled\nwith `cc@1.6.0` or later on a Unix host. This affects any build that depends on\n`libz-sys`. Cargo saves build script stdout under `target/`, so the values end\nup in anything that stores or shares the `target/` directory, such as CI caches.\n\nThis is similar to the [Miri issue](https://blog.rust-lang.org/2026/09/21/github-actions-leaking-secrets-when-miri-output-is-cached/).\n\n## Details\n\nTo decide whether to link against a system zlib, the `libz-sys` build script\ncompiles a small test program with a compiler command from `cc` and logs it\nwith:\n\n```rust\nprintln!(\"running {:?}\", cmd);\n```\n\nOn Unix, `Debug` impl for `std::process::Command` prints every environment\nvariable explicitly set on the command. Before `cc@1.6.0`, its\n`Tool::to_command()` set only a few compiler-specific variables. Starting with\n`cc@1.6.0` (released 2026-10-03), `Tool::to_command()` clears the environment\nand sets every variable explicitly.\n\nCargo parses build script stdout for `cargo:` directives, and stores the full\noutput in the build directory. It also prints it with `-vv`.\n\nThe probe runs for a default `libz-sys` build, including when pkg-config finds\nzlib, unless one of these applies:\n\n* the target is Windows, Android, Haiku or OpenHarmony\n* static linking is requested via the `static` feature or `LIBZ_SYS_STATIC=1`\n* the `zlib-ng` features are enabled without `stock-zlib`\n\n## Mitigations\n\nFixed in `libz-sys@1.1.31`, which no longer logs the probe command.\n\nIf you cannot upgrade, here are some workarounds:\n\n* Build with `LIBZ_SYS_STATIC=1` or the `static` feature, which skips the probe.\n* Pin `cc` to a release before 1.6.0 (`cargo update cc --precise \u003cversion\u003e`).\n\nNote that upgrading `libz-sys` does not remove values already written. If an\naffected build already ran with secrets in its environment, clear CI caches and\nstored artifacts containing its\n[target/build directory](https://doc.rust-lang.org/nightly/cargo/reference/build-cache.html#build-cache),\nand consider rotating those secrets.","facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"published":"2026-10-28T12:00:00Z","modified":"2026-10-29T14:15:02Z","fixes":[{"ecosystem":"crates.io","package":"libz-sys","fixed_in":["1.1.31"],"sources":["osv"]}],"affected":[{"source":"osv","ecosystem":"crates.io","package":"libz-sys","ranges":[{"type":"SEMVER","events":[{"introduced":"1.0.21"},{"fixed":"1.1.31"}]}]}],"references":[{"url":"https://crates.io/crates/libz-sys","tags":["package"]},{"url":"https://rustsec.org/advisories/RUSTSEC-2026-0418.html","tags":["advisory"]},{"url":"https://github.com/rust-lang/libz-sys/pull/280","tags":["web"]}],"sources":{"osv":[{"id":"RUSTSEC-2026-0418","title":"libz-sys build script leaks environment variables in the build directory","description":"The build script of `libz-sys` version \u003c= 1.1.30 prints the full environment\nof the build, including any secrets it contains, to its stdout when compiled\nwith `cc@1.6.0` or later on a Unix host. This affects any build that depends on\n`libz-sys`. Cargo saves build script stdout under `target/`, so the values end\nup in anything that stores or shares the `target/` directory, such as CI caches.\n\nThis is similar to the [Miri issue](https://blog.rust-lang.org/2026/09/21/github-actions-leaking-secrets-when-miri-output-is-cached/).\n\n## Details\n\nTo decide whether to link against a system zlib, the `libz-sys` build script\ncompiles a small test program with a compiler command from `cc` and logs it\nwith:\n\n```rust\nprintln!(\"running {:?}\", cmd);\n```\n\nOn Unix, `Debug` impl for `std::process::Command` prints every environment\nvariable explicitly set on the command. Before `cc@1.6.0`, its\n`Tool::to_command()` set only a few compiler-specific variables. Starting with\n`cc@1.6.0` (released 2026-10-03), `Tool::to_command()` clears the environment\nand sets every variable explicitly.\n\nCargo parses build script stdout for `cargo:` directives, and stores the full\noutput in the build directory. It also prints it with `-vv`.\n\nThe probe runs for a default `libz-sys` build, including when pkg-config finds\nzlib, unless one of these applies:\n\n* the target is Windows, Android, Haiku or OpenHarmony\n* static linking is requested via the `static` feature or `LIBZ_SYS_STATIC=1`\n* the `zlib-ng` features are enabled without `stock-zlib`\n\n## Mitigations\n\nFixed in `libz-sys@1.1.31`, which no longer logs the probe command.\n\nIf you cannot upgrade, here are some workarounds:\n\n* Build with `LIBZ_SYS_STATIC=1` or the `static` feature, which skips the probe.\n* Pin `cc` to a release before 1.6.0 (`cargo update cc --precise \u003cversion\u003e`).\n\nNote that upgrading `libz-sys` does not remove values already written. If an\naffected build already ran with secrets in its environment, clear CI caches and\nstored artifacts containing its\n[target/build directory](https://doc.rust-lang.org/nightly/cargo/reference/build-cache.html#build-cache),\nand consider rotating those secrets.","status":"published","published":"2026-10-28T12:00:00Z","modified":"2026-10-29T14:15:02.333141406Z","updated_at":"2026-11-02T15:53:40.430679Z"}]}}