---
id: CVE-2026-57585
title: >-
  msgpack: MessagePack for Python: Denial of Service via Unpacker reuse after
  error (CVE-2026-57585)
summary: >-
  A flaw was found in MessagePack for Python, a serializer implementation. This
  vulnerability, categorized as a Use-After-Free (CWE-416), occurs when the
  Unpacker component is reused after an error. A remote attacker could exploit
  this by re…
severity: high
cvss: 7.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'
cvssSource: vendor
cwe: CWE-125
vendor: Red Hat
product: Red Hat AI Inference Server 3.4
affected:
  - ai_inference_server 3.4
patched:
  - ai_inference_server 3.4
published: '2026-06-30'
updated: '2026-09-24'
sourceUpdated: '2026-09-24T05:56:14+00:00'
source: CSAF
sourceUrl: 'https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-57585.json'
references:
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-57585.json
  - url: 'https://access.redhat.com/security/cve/CVE-2026-57585'
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2496020'
  - url: 'https://www.cve.org/CVERecord?id=CVE-2026-57585'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-57585'
  - url: >-
      https://github.com/msgpack/msgpack-python/commit/2c56ddb5d0025ed481d962c0f5d62d19dec7476d
  - url: >-
      https://github.com/msgpack/msgpack-python/security/advisories/GHSA-6v7p-g79w-8964
  - url: 'https://access.redhat.com/errata/RHSA-2026:70965'
  - url: 'https://access.redhat.com/errata/RHSA-2026:70979'
  - url: 'https://access.redhat.com/errata/RHSA-2026:70995'
  - url: 'https://github.com/msgpack/msgpack-python'
  - url: 'https://github.com/msgpack/msgpack-python/releases/tag/v1.2.1'
tags:
  - csaf
  - vex
  - red-hat
  - osv
  - pip
epss: 0.00488
epssPercentile: 0.39332
aliases:
  - GHSA-6v7p-g79w-8964
  - PYSEC-2026-3625
ecosystem: pip
ingestedAt: '2026-07-08T18:25:46.532Z'
---

## Overview

A flaw was found in MessagePack for Python, a serializer implementation. This vulnerability, categorized as a Use-After-Free (CWE-416), occurs when the Unpacker component is reused after an error. A remote attacker could exploit this by repeatedly providing untrusted input, leading to an out-of-bounds read and a system crash. This can result in a Denial of Service (DoS) attack.

## Vendor advisories

- **RHSA-2026:70965** · Red Hat · fixed in: Red Hat AI Inference Server 3.4 · released 2026-09-23 · [advisory](https://access.redhat.com/errata/RHSA-2026:70965)
- **RHSA-2026:70979** · Red Hat · fixed in: Red Hat AI Inference Server 3.4 · released 2026-09-23 · [advisory](https://access.redhat.com/errata/RHSA-2026:70979)
- **RHSA-2026:70995** · Red Hat · fixed in: Red Hat AI Inference Server 3.4 · released 2026-09-23 · [advisory](https://access.redhat.com/errata/RHSA-2026:70995)

**msgpack: MessagePack for Python: Denial of Service via Unpacker reuse after error** — rated Important by Red Hat. Released 2026-06-30, updated 2026-09-24.

Fixed:

- Red Hat AI Inference Server 3.4

Not affected:

- Pen Drive Powered by Red Hat Lightspeed
- Red Hat AI Inference Server
- Red Hat Ansible Automation Platform 2
- Red Hat Enterprise Linux 10
- Red Hat Enterprise Linux 8
- Red Hat Enterprise Linux 9
- Red Hat Enterprise Linux AI (RHEL AI) 3
- Red Hat OpenShift AI (RHOAI)
- Red Hat OpenShift Container Platform 4
- Red Hat OpenStack Platform 16.2

## Remediation

For more information visit https://access.redhat.com/errata/RHSA-2026:70965 https://access.redhat.com/errata/RHSA-2026:70965
For more information visit https://access.redhat.com/errata/RHSA-2026:70979 https://access.redhat.com/errata/RHSA-2026:70979
For more information visit https://access.redhat.com/errata/RHSA-2026:70995 https://access.redhat.com/errata/RHSA-2026:70995

Workarounds / mitigations:

- To mitigate this issue, applications utilizing MessagePack for Python should be reviewed to ensure that `Unpacker` instances are not reused after an error has occurred during unpacking. Instead, a new `Unpacker` instance should be created for subsequent operations.

## Package advisory (CVE-2026-57585)

Affected packages:

- `msgpack < 1.2.1`

Patched in:

- `msgpack 1.2.1`

Source: https://osv.dev/vulnerability/GHSA-6v7p-g79w-8964