The libz-sys crate versions 1.0.21 up to but not including 1.1.31 contain a build script vulnerability where the full build environment, including secrets, is printed to stdout during compilation with cc version 1.6.0 or later on Unix hosts. This output is saved by Cargo in the build directory, potentially exposing sensitive environment variables in shared or cached build artifacts. The issue is fixed in libz-sys version 1.1.31.