# CVE-2026-105280: Hex writes unverified package tarballs to standard output in mix hex.package fetch

Status: published. Published: 2026-10-12. Updated: 2026-11-11.

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 tarball's inner and outer checksums with the repository's 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 doesn't 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 mirror's 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.

## Remediation

- fix: Upgrade Hex to 2.5.2 or later, for example with mix local.hex. mix hex.package fetch PACKAGE VERSION --output - then verifies the registry checksum before writing the tarball to standard output and prints its messages to standard error. (source: CNA: EEF)
- workaround: Write the tarball to a file with --output FILE, which verifies the checksums, and read that file instead of standard output. (source: CNA: EEF)
- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: CNA: EEF) — https://github.com/hexpm/hex/commit/8a14632ca6ba8a8afd2a3f2098bc267c13e13d93
- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: CNA: EEF) — https://github.com/hexpm/hex/commit/69489f8b74213f03db10169e6e5407e6d5fee512

## Affected products and versions

- hexpm / hex (hex): ≥ 0.20.2; < 2.5.2 (affected, semver). Source: CNA: EEF
- hexpm / hex (hexpm/hex): ≥ d1f5a085d9d4748e1f7d195e4bc39ebd77c28d9c; < * (affected, git); unaffected at 8a14632ca6ba8a8afd2a3f2098bc267c13e13d93; unaffected at 69489f8b74213f03db10169e6e5407e6d5fee512. Source: CNA: EEF

## Severity and prioritization

- CVSS 4.0: 6.9 (medium); CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:A/VC:N/VI:H/VA:N/SC:N/SI:H/SA:N; source: CNA: EEF

- CISA KEV: No listing in collected sources

- EPSS: 0.21% as of 2026-11-10; percentile 11.36%

- SSVC: exploitation none; automatable no; technical impact partial; source ADP: CISA-ADP

- Weaknesses: CWE-354

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://github.com/hexpm/hex/security/advisories/GHSA-98jr-23pm-vj7c (CNA: EEF; related, vendor-advisory)

- https://cna.erlef.org/cves/CVE-2026-105280.html (CNA: EEF; related)

- https://osv.dev/vulnerability/EEF-CVE-2026-105280 (CNA: EEF; related)

- https://github.com/hexpm/hex/commit/d1f5a085d9d4748e1f7d195e4bc39ebd77c28d9c (CNA: EEF; related)

- https://github.com/hexpm/hex/commit/8a14632ca6ba8a8afd2a3f2098bc267c13e13d93 (CNA: EEF; patch)

- https://github.com/hexpm/hex/commit/69489f8b74213f03db10169e6e5407e6d5fee512 (CNA: EEF; patch)

## Provenance

- CNA: EEF: https://www.cve.org/CVERecord?id=CVE-2026-105280; retrieved 2026-11-11; source updated 2026-11-11

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-105280; retrieved 2026-11-11; source updated Not reported

Revision: eaf38ae0c900ef9213bd79fc5be0601fa35ac23adbfde1d4b297153fc2a593cf

Canonical: https://y2.dev/cve/CVE-2026-105280

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