---
id: CVE-2026-26209
title: >-
  cbor2: cbor2: Denial of Service due to uncontrolled recursion via crafted CBOR
  payloads (CVE-2026-26209)
summary: >-
  A flaw was found in cbor2, a library for encoding and decoding Concise Binary
  Object Representation (CBOR) data. A remote attacker can exploit this
  vulnerability by sending a specially crafted CBOR payload containing deeply
  nested structur…
severity: medium
cvss: 5.5
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H'
cvssSource: vendor
cwe: CWE-770
vendor: Red Hat
product: Red Hat Enterprise Linux AI (RHEL AI) 3
affected:
  - ai_inference_server
  - ansible_automation_platform 2
  - enterprise_linux_ai_rhel_ai 3
  - openshift_ai_rhoai
  - ai_inference_server 3.2
  - ai_inference_server 3.3
patched:
  - ai_inference_server 3.2
  - ai_inference_server 3.3
published: '2026-03-23'
updated: '2026-09-21'
sourceUpdated: '2026-09-21T17:22:42+00:00'
source: CSAF
sourceUrl: 'https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-26209.json'
references:
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-26209.json
  - url: 'https://access.redhat.com/security/cve/CVE-2026-26209'
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2450422'
  - url: 'https://www.cve.org/CVERecord?id=CVE-2026-26209'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-26209'
  - url: >-
      https://github.com/agronholm/cbor2/commit/e61a5f365ba610d5907a0ae1bc72769bba34294b
  - url: 'https://github.com/agronholm/cbor2/pull/275'
  - url: 'https://github.com/agronholm/cbor2/releases/tag/5.9.0'
  - url: 'https://github.com/agronholm/cbor2/security/advisories/GHSA-3c37-wwvx-h642'
  - url: 'https://access.redhat.com/errata/RHSA-2026:19724'
  - url: 'https://access.redhat.com/errata/RHSA-2026:19725'
  - url: 'https://access.redhat.com/errata/RHSA-2026:16030'
  - url: 'https://access.redhat.com/errata/RHSA-2026:16009'
  - url: 'https://access.redhat.com/errata/RHSA-2026:16174'
  - url: 'https://github.com/agronholm/cbor2'
tags:
  - csaf
  - vex
  - red-hat
  - osv
  - pip
  - score-dispute
epss: 0.00649
epssPercentile: 0.48942
aliases:
  - GHSA-3c37-wwvx-h642
  - PYSEC-2026-2123
ecosystem: pip
scores:
  vendor: 5.5
  osv: 7.5
ingestedAt: '2026-07-13T18:57:51.809Z'
---

## Overview

A flaw was found in cbor2, a library for encoding and decoding Concise Binary Object Representation (CBOR) data. A remote attacker can exploit this vulnerability by sending a specially crafted CBOR payload containing deeply nested structures. This can cause the application to crash due to uncontrolled recursion, leading to a complete Denial of Service (DoS) for the affected application.

## Vendor advisories

- **RHSA-2026:19724** · Red Hat · fixed in: Red Hat AI Inference Server 3.2 · released 2026-05-20 · [advisory](https://access.redhat.com/errata/RHSA-2026:19724)
- **RHSA-2026:19725** · Red Hat · fixed in: Red Hat AI Inference Server 3.2 · released 2026-05-20 · [advisory](https://access.redhat.com/errata/RHSA-2026:19725)
- **RHSA-2026:16030** · Red Hat · fixed in: Red Hat AI Inference Server 3.3 · released 2026-05-11 · [advisory](https://access.redhat.com/errata/RHSA-2026:16030)
- **RHSA-2026:16009** · Red Hat · fixed in: Red Hat AI Inference Server 3.3 · released 2026-05-11 · [advisory](https://access.redhat.com/errata/RHSA-2026:16009)
- **RHSA-2026:16174** · Red Hat · fixed in: Red Hat AI Inference Server 3.3 · released 2026-05-12 · [advisory](https://access.redhat.com/errata/RHSA-2026:16174)
- **Red Hat VEX** · Moderate · affected: Red Hat AI Inference Server, Red Hat Ansible Automation Platform 2, Red Hat Enterprise Linux AI (RHEL AI) 3, Red Hat OpenShift AI (RHOAI) · no fix planned: Red Hat AI Inference Server, Red Hat Ansible Automation Platform 2, Red Hat Enterprise Linux AI (RHEL AI) 3, Red Hat OpenShift AI (RHOAI) · updated 2026-09-21 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-26209.json)

**cbor2: cbor2: Denial of Service due to uncontrolled recursion via crafted CBOR payloads** — rated Moderate by Red Hat. Released 2026-03-23, updated 2026-09-21.

Affected:

- Red Hat AI Inference Server
- Red Hat Ansible Automation Platform 2
- Red Hat Enterprise Linux AI (RHEL AI) 3
- Red Hat OpenShift AI (RHOAI)

Fixed:

- Red Hat AI Inference Server 3.2
- Red Hat AI Inference Server 3.3

No fix planned:

- Red Hat AI Inference Server
- Red Hat Ansible Automation Platform 2
- Red Hat Enterprise Linux AI (RHEL AI) 3
- Red Hat OpenShift AI (RHOAI)

## Remediation

For more information visit https://access.redhat.com/errata/RHSA-2026:19724 https://access.redhat.com/errata/RHSA-2026:19724
For more information visit https://access.redhat.com/errata/RHSA-2026:19725 https://access.redhat.com/errata/RHSA-2026:19725
For more information visit https://access.redhat.com/errata/RHSA-2026:16030 https://access.redhat.com/errata/RHSA-2026:16030

## Package advisory (CVE-2026-26209)

Affected packages:

- `cbor2 < 5.9.0`

Patched in:

- `cbor2 5.9.0`

Source: https://osv.dev/vulnerability/GHSA-3c37-wwvx-h642