---
id: CVE-2026-96618
title: >-
  Improper Handling of Highly Compressed Data (Data Amplification) vulnerability
  in hexpm hex allows an untrusted package mirror to exhaust the memory or disk
  space of the machine running mix deps.get, mix deps.update, mix hex.package
  fetc…
summary: >-
  Improper Handling of Highly Compressed Data (Data Amplification) vulnerability
  in hexpm hex allows an untrusted package mirror to exhaust the memory or disk
  space of the machine running mix deps.get, mix deps.update, mix hex.package
  fetc…
severity: none
cwe:
  - CWE-409
  - CWE-770
published: '2026-10-12'
updated: '2026-10-12'
sourceUpdated: '2026-10-12T16:17:07.920'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-96618'
references:
  - url: 'https://cna.erlef.org/cves/CVE-2026-96618.html'
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: >-
      https://github.com/hexpm/hex/commit/08956100a8283ba500a123e5539ac64d5d7e91d8
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: >-
      https://github.com/hexpm/hex/commit/51ea632424fb6ea8765148f96dc25dfeb526b1f8
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: >-
      https://github.com/hexpm/hex/commit/bb5189eade682c5fc3f98d9725973a7beb4e1deb
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: 'https://github.com/hexpm/hex/security/advisories/GHSA-gf42-pg2f-63jp'
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: 'https://osv.dev/vulnerability/EEF-CVE-2026-96618'
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
tags:
  - nvd
ingestedAt: '2026-10-12T16:57:59.921Z'
---

## Overview

Improper Handling of Highly Compressed Data (Data Amplification) vulnerability in hexpm hex allows an untrusted package mirror to exhaust the memory or disk space of the machine running mix deps.get, mix deps.update, mix hex.package fetch or mix hex.docs fetch.

Hex treats a mirror configured with HEX_MIRROR_URL, HEX_MIRROR or mirror_url as untrusted: it doesn't send credentials to it, and it checks registry signatures and package checksums that the mirror can't forge. Several response paths consume memory or disk in proportion to what the mirror sends before any of those checks run.

Hex.HTTP.request/5 reads the whole response body into memory and decompresses it with :zlib.gunzip/1 whenever the response's Content-Encoding contains gzip, with no limit on the compressed or decompressed size. Hex doesn't ask for compressed responses, so the server decides whether this step runs. It applies to registry, package, docs and API responses.

Package tarballs have no download size limit. Hex 2.5.1 holds the whole tarball in memory and writes it to the cache, and the development branch streams it to a temporary file; the 16 MiB tarball limit is checked only when the file is unpacked. The tarball is then unpacked, into deps/<app> in 2.5.1 and into a staging directory on the development branch, before its checksums are compared with the registry.

mix hex.docs fetch, and mix hex.docs offline when docs are missing, write the docs tarball to disk and extract it with :mix_hex_erl_tar.extract/2 without the 16 MiB compressed and 128 MiB decompressed limits that mix_hex_tarball:unpack_docs/3 applies. The signed registry doesn't cover docs tarballs, so nothing checks them.

Registry responses are also decompressed before their signature is checked, in hex_core code that Hex vendors; that part is tracked in https://github.com/hexpm/hex_core/security/advisories/GHSA-7c4r-cgf9-9jmq.

This issue affects hex: from 0.11.2 before 2.5.2.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.