# CVE-2026-105274: hex_core decompresses registry and Erlang term API responses without size limits

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

Improper Handling of Highly Compressed Data (Data Amplification) vulnerability in hexpm hex_core allows an untrusted repository mirror, or a server answering hex_core's API requests, to exhaust the memory of the Erlang VM running hex_core. The same code is vendored in Hex (mix_hex_repo, mix_hex_api) and rebar3 (r3_hex_repo, r3_hex_api).

hex_repo:get_names/1, hex_repo:get_versions/1, hex_repo:get_package/2 and hex_repo:get_policy/2 decompress the registry response with zlib:gunzip/1 and decode the signed envelope before verifying its signature. A mirror doesn't have the repository's private key, but it chooses the compressed bytes, so a small response decompresses into an envelope of any size before the signature check rejects it.

hex_api decodes responses with the application/vnd.hex+erlang content type through hex_safe_binary_to_term:safe_binary_to_term/1, which calls binary_to_term(Binary, [safe]). The safe option prevents atom creation, but it accepts compressed terms and doesn't limit the size of the decoded term, and the check that rejects functions and ports runs after the term has been built. The fix for CVE-2026-21619 added the safe option and that check without bounding the decoded size.

This issue affects rebar3: from 3.9.1 before 3.27.3; hex: from 2.1.0 before 2.5.2 and from 2.6.0 onward; hex_core: from 0.1.0 before 0.20.0.

## Remediation

- fix: Upgrade hex_core to 0.20.0 or later. Registry resources larger than 16 MiB after decompression are rejected with {too_big_uncompressed, MaxSize}, configurable with registry_max_uncompressed_size.

Upgrade Hex to 2.5.2 or later, which vendors hex_core 0.20.0. No rebar3 release vendors hex_core 0.20.0 yet. (source: CNA: EEF)
- workaround: Point repository URLs at repo.hex.pm or a mirror you operate, and the API URL at hex.pm. (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_core/commit/ebe25d110717f6a3addba5232cd4a7dc1c76b628
- 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/erlang/rebar3/commit/360838a22f5b3a88c0358207f2923059bcbb3afb
- 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/d8b60eee97abb119d525306f048969a217d793a5

## Affected products and versions

- hexpm / hex_core (hex_core): ≥ 0.1.0; < 0.20.0 (affected, semver). Source: CNA: EEF
- hexpm / hex_core (hexpm/hex_core): ≥ fbb6d9de472e5edb8d6fb6b32a91cb266137892e; < ebe25d110717f6a3addba5232cd4a7dc1c76b628 (affected, git). Source: CNA: EEF
- erlang / rebar3 (rebar3): ≥ 3.9.1; < 3.27.3 (affected, semver). Source: CNA: EEF
- erlang / rebar3 (erlang/rebar3): ≥ 209c02ec57c2cc3207ee0174c3af3675b8dc8f79; < 360838a22f5b3a88c0358207f2923059bcbb3afb (affected, git). Source: CNA: EEF
- hexpm / hex (hex): ≥ 2.1.0; < 2.5.2 (affected, semver); ≥ 2.6.0; < * (affected, semver). Source: CNA: EEF
- hexpm / hex (hexpm/hex): ≥ 671f695ac548ed01f5828c2a739ecaa942b21007; < d8b60eee97abb119d525306f048969a217d793a5 (affected, git). Source: CNA: EEF

## Severity and prioritization

- CVSS 4.0: 2.1 (low); CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:A/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N; source: CNA: EEF

- CISA KEV: No listing in collected sources

- EPSS: 0.45% as of 2026-11-10; percentile 39.21%

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

- Weaknesses: CWE-409

## Exploit evidence

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

## References

- https://github.com/hexpm/hex_core/security/advisories/GHSA-7c4r-cgf9-9jmq (CNA: EEF; related, vendor-advisory)

- https://cna.erlef.org/cves/CVE-2026-105274.html (CNA: EEF; related)

- https://osv.dev/vulnerability/EEF-CVE-2026-105274 (CNA: EEF; related)

- https://github.com/hexpm/hex_core/commit/fbb6d9de472e5edb8d6fb6b32a91cb266137892e (CNA: EEF; related)

- https://github.com/hexpm/hex_core/commit/ebe25d110717f6a3addba5232cd4a7dc1c76b628 (CNA: EEF; patch)

- https://github.com/erlang/rebar3/commit/209c02ec57c2cc3207ee0174c3af3675b8dc8f79 (CNA: EEF; related)

- https://github.com/erlang/rebar3/commit/360838a22f5b3a88c0358207f2923059bcbb3afb (CNA: EEF; patch)

- https://github.com/hexpm/hex/commit/671f695ac548ed01f5828c2a739ecaa942b21007 (CNA: EEF; related)

- https://github.com/hexpm/hex/commit/d8b60eee97abb119d525306f048969a217d793a5 (CNA: EEF; patch)

## Provenance

- CNA: EEF: https://www.cve.org/CVERecord?id=CVE-2026-105274; retrieved 2026-11-11; source updated 2026-11-11

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-105274; retrieved 2026-11-11; source updated Not reported

Revision: 371e33175efde890a5a32c4f2a50784be5192f4fce6cfbb95a3cd19cab518335

Canonical: https://y2.dev/cve/CVE-2026-105274

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