---
id: CVE-2026-49265
title: >-
  OAuthLib is an implementation of the OAuth request-signing logic for Python
  3.6+
summary: >-
  OAuthLib is an implementation of the OAuth request-signing logic for Python
  3.6+. From 3.0.0 until 4.0.0, OAuthLib's PKCE checks in
  oauthlib/oauth2/rfc6749/grant_types/authorization_code.py compare
  attacker-supplied code_verifier values …
severity: medium
cvss: 6.8
cvssVector: 'CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N'
cwe:
  - CWE-208
vendor: oauthlib
product: oauthlib
affected:
  - 'oauthlib >= 3.0.0, < 4.0.0'
patched:
  - oauthlib 4.0.0
published: '2026-10-13'
updated: '2026-10-16'
sourceUpdated: '2026-10-16T20:04:29.760'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-49265'
references:
  - url: >-
      https://github.com/oauthlib/oauthlib/commit/74664d3fe037a354e180e305135c6bab1747a6b0
    label: security-advisories@github.com
  - url: 'https://github.com/oauthlib/oauthlib/pull/963'
    label: security-advisories@github.com
  - url: 'https://github.com/oauthlib/oauthlib/releases/tag/v4.0.0'
    label: security-advisories@github.com
  - url: >-
      https://github.com/oauthlib/oauthlib/security/advisories/GHSA-xpv3-w29h-x7cv
    label: security-advisories@github.com
  - url: >-
      https://github.com/pypa/advisory-database/tree/main/vulns/oauthlib/PYSEC-2026-4114.yaml
    label: security-advisories@github.com
  - url: >-
      https://github.com/oauthlib/oauthlib/commit/40b0ab56da3682c2484a4b78bbff309f8025d950
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-49265'
  - url: 'https://github.com/advisories/GHSA-xpv3-w29h-x7cv'
  - url: 'https://github.com/oauthlib/oauthlib'
  - url: 'https://pypi.org/project/oauthlib'
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-49265.json
  - url: 'https://access.redhat.com/security/cve/CVE-2026-49265'
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2550336'
  - url: 'https://www.cve.org/CVERecord?id=CVE-2026-49265'
  - url: 'https://access.redhat.com/errata/RHSA-2026:82415'
  - url: 'https://access.redhat.com/errata/RHSA-2026:82368'
tags:
  - nvd
  - ghsa
  - pip
  - osv
  - csaf
  - vex
  - red-hat
  - cve.org
epss: 0.00242
epssPercentile: 0.15309
aliases:
  - GHSA-xpv3-w29h-x7cv
  - PYSEC-2026-4114
ecosystem: pip
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: total
  timestamp: '2026-10-13T16:19:32.600149Z'
ingestedAt: '2026-09-29T18:42:35.834Z'
---

## Overview

OAuthLib is an implementation of the OAuth request-signing logic for Python 3.6+. From 3.0.0 until 4.0.0, OAuthLib's PKCE checks in oauthlib/oauth2/rfc6749/grant_types/authorization_code.py compare attacker-supplied code_verifier values with stored challenges using ordinary string equality in code_challenge_method_plain and code_challenge_method_s256. Because the comparison can return after a length difference or the first mismatching character, repeated token endpoint measurements can reveal common-prefix timing information that could potentially allow recovery of the code_verifier, unauthorized access-token acquisition, and account takeover. Practical exploitation requires an intercepted, single-use authorization code and enough measurements to overcome real-world network noise; the local timing benchmark does not establish practical remote account takeover, so the weakness remains a defense-in-depth concern. This issue is fixed in version 4.0.0.

## Remediation

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

## Package advisory (CVE-2026-49265)

Affected packages:

- `oauthlib >= 3.0.0, < 4.0.0`

Patched in:

- `oauthlib 4.0.0`

Source: https://github.com/advisories/GHSA-xpv3-w29h-x7cv

## Vendor advisories

- **RHSA-2026:82415** · Red Hat · fixed in: Red Hat AI Inference Server 3.5 · released 2026-10-13 · [advisory](https://access.redhat.com/errata/RHSA-2026:82415)
- **RHSA-2026:82368** · Red Hat · fixed in: Red Hat AI Inference Server 3.5 · released 2026-10-13 · [advisory](https://access.redhat.com/errata/RHSA-2026:82368)
- **Red Hat VEX** · Moderate · affected: Confidential Compute Attestation, Fence Agents Remediation Operator, Lightspeed Core, Lightspeed Services for Advanced Cluster Management, Migration Toolkit for Applications 8, Migration Toolkit for Containers, … · no fix planned: Confidential Compute Attestation, Fence Agents Remediation Operator, Lightspeed Core, Lightspeed Services for Advanced Cluster Management, … · updated 2026-10-16 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-49265.json)