CVE-2026-43965

Description

Path traversal vulnerability in Gleam's dependency management allows arbitrary directory deletion via malicious build/packages/packages.toml content. Package keys read from build/packages/packages.toml by LocalPackages::read_from_disc are passed without validation to paths.build_packages_package(), which constructs a filesystem path by joining the project build directory with the attacker-controlled key. The resulting path is then passed to fs::delete_directory (which calls remove_dir_all). No check is performed to ensure the path remains within the intended build/packages/ directory. Both absolute paths and relative traversal sequences (e.g. ../) are accepted as package keys, allowing deletion of arbitrary directories. An attacker who can cause a victim to run gleam deps download on a project containing a malicious build/packages/packages.toml (e.g. by committing the normally-gitignored file to a repository) can cause arbitrary directories on the victim's system to be recursively deleted. This issue affects Gleam from 0.18.0-rc1 until 1.17.0.

References

• https://cna.erlef.org/cves/CVE-2026-43965.html
• https://github.com/gleam-lang/gleam/commit/690ca069817bee5f77a28fc3e360627c1da19291
• https://github.com/gleam-lang/gleam/security/advisories/GHSA-jqvf-f6p2-wrv3
• https://osv.dev/vulnerability/EEF-CVE-2026-43965
• https://github.com/gleam-lang/gleam/security/advisories/GHSA-jqvf-f6p2-wrv3