Improper Validation of Integrity Check Value vulnerability in hexpm hex allows a package mirror to substitute the tarball that mix hex.package fetch PACKAGE VERSION –output - writes to standard output.
Hex compares a fetched tarballs inner and outer checksums with the repositorys signed registry before writing it to a file or unpacking it. The standard output branch of mix hex.package fetch writes the bytes returned by Hex.SCM.fetch/3 without that comparison, and Hex.SCM.fetch/3 doesnt verify freshly downloaded tarballs itself. When a mirror configured with HEX_MIRROR_URL or mirror_url serves altered bytes, the command prints them and exits successfully, while the same fetch with –output FILE fails with a checksum mismatch.
Hex also prints diagnostics to standard output while the command runs: the body of a failed HTTP response from the update check or a registry fetch, and API warnings from the x-hex-message header. A mirror that answers one of those requests with an error whose body is a tar archive gets that archive written to standard output ahead of the verified tarball, so a pipeline that unpacks standard output extracts the mirrors files. This happens even when the checksum check then fails, because the archive is already on standard output.
This issue affects hex: from 0.20.2 before 2.5.2.
Weakness
The product does not validate or incorrectly validates the integrity check values or “checksums” of a message. This may prevent it from detecting if the data has been modified or corrupted in transmission.
Potential Mitigations
Related Attack Patterns
- https://cwe.mitre.org/data/definitions/145.html
- https://cwe.mitre.org/data/definitions/463.html
- https://cwe.mitre.org/data/definitions/75.html
References
- https://cna.erlef.org/cves/CVE-2026-105280.html
- https://github.com/hexpm/hex/commit/69489f8b74213f03db10169e6e5407e6d5fee512
- https://github.com/hexpm/hex/commit/8a14632ca6ba8a8afd2a3f2098bc267c13e13d93
- https://github.com/hexpm/hex/commit/d1f5a085d9d4748e1f7d195e4bc39ebd77c28d9c
- https://github.com/hexpm/hex/security/advisories/GHSA-98jr-23pm-vj7c
- https://osv.dev/vulnerability/EEF-CVE-2026-105280