Vulnerability-Lookup

BREW-ANSIBLE-CVE-2026-49265 (GHSA-XPV3-W29H-X7CV)

Vulnerability from osv_homebrew – Published: 2026-09-30 18:44 – Updated: 2026-10-02 08:50 – Source website

Summary

Oauthlib: Timing Attack Vulnerability in PKCE code_verifier Comparison (CWE-208)

Details

Summary

A timing side-channel vulnerability exists in the PKCE (RFC 7636) implementation of the Authorization Code Grant flow. The code_challenge_method_plain function uses Python's standard == operator for string comparison instead of a constant-time comparison function, potentially allowing timing-based attacks.

Affected Component

File: oauthlib/oauth2/rfc6749/grant_types/authorization_code.py
Functions: code_challenge_method_plain, code_challenge_method_s256
Vulnerability Type: CWE-208 (Observable Timing Discrepancy)

Technical Details

Python's == operator uses short-circuit evaluation when comparing strings: 1. Returns False immediately if lengths differ 2. Compares characters left-to-right, stopping at first mismatch

This means comparison time varies linearly with the length of the common prefix between the attacker-supplied verifier and the stored challenge, creating a measurable timing oracle.

Proof of Concept

Tested locally against oauthlib source (network jitter eliminated to isolate pure Python execution time):

Input	Result	Time (10M iterations)
Wrong first char (`B` + `A`*49)	Fast reject	0.34106s
49 chars correct (`A`*49 + `B`)	Deep compare	0.37847s
Difference		0.03741s

The ~37ms delta over 10M iterations corresponds to nanosecond-level differences per call, which are statistically exploitable under controlled conditions.

Attack Scenario

Attacker intercepts authorization_code via Custom URI Scheme Hijacking
PKCE blocks token request — attacker lacks code_verifier
Attacker sends repeated requests to /token endpoint measuring response times
Using timing oracle, attacker recovers code_verifier character by character
Attacker obtains Access Token → Account Takeover

Note: Practical exploitability is limited due to the single-use nature of authorization codes and real-world network noise. However, the vulnerable pattern should be corrected as a defense-in-depth measure.

Recommended Fix

Replace == with hmac.compare_digest() for constant-time comparison:

cr: Elvin Latifli

Severity

6.8 (Medium)


                    
                      CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N

References

URL

Type

	https://github.com/oauthlib/oauthlib/security/adv…	WEB
	https://github.com/oauthlib/oauthlib/pull/963	WEB
	https://github.com/oauthlib/oauthlib/commit/40b0a…	WEB
	https://github.com/oauthlib/oauthlib	PACKAGE

JSON

To clipboard

{
  "affected": [
    {
      "ecosystem_specific": {
        "fix": "bump",
        "range_state": "fixed",
        "resource": "oauthlib",
        "resource_purl": "pkg:pypi/oauthlib@4.0.0",
        "upstream_fixed_in": "4.0.0"
      },
      "package": {
        "ecosystem": "Homebrew",
        "name": "ansible",
        "purl": "pkg:brew/ansible"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "2.8.4_1"
            },
            {
              "fixed": "14.4.0_1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "database_specific": {
    "confidence": "high",
    "source": "matched",
    "strategy": "registry",
    "upstream_evidence": [
      {
        "ecosystem": "PyPI",
        "key": "pkg:pypi/oauthlib@4.0.0",
        "name": "oauthlib",
        "resource": "oauthlib",
        "strategy": "registry",
        "subject_version": "4.0.0"
      }
    ]
  },
  "details": "## Summary\n\nA timing side-channel vulnerability exists in the PKCE (RFC 7636) implementation \nof the Authorization Code Grant flow. The `code_challenge_method_plain` function \nuses Python\u0027s standard `==` operator for string comparison instead of a \nconstant-time comparison function, potentially allowing timing-based attacks.\n\n## Affected Component\n\n- File: `oauthlib/oauth2/rfc6749/grant_types/authorization_code.py`\n- Functions: `code_challenge_method_plain`, `code_challenge_method_s256`\n- Vulnerability Type: CWE-208 (Observable Timing Discrepancy)\n\n## Technical Details\n\nPython\u0027s `==` operator uses short-circuit evaluation when comparing strings:\n1. Returns `False` immediately if lengths differ\n2. Compares characters left-to-right, stopping at first mismatch\n\nThis means comparison time varies linearly with the length of the common prefix \nbetween the attacker-supplied verifier and the stored challenge, creating a \nmeasurable timing oracle.\n\n## Proof of Concept\n\nTested locally against oauthlib source (network jitter eliminated to isolate \npure Python execution time):\n\n| Input | Result | Time (10M iterations) |\n|---|---|---|\n| Wrong first char (`B` + `A`*49) | Fast reject | 0.34106s |\n| 49 chars correct (`A`*49 + `B`) | Deep compare | 0.37847s |\n| **Difference** | | **0.03741s** |\n\nThe ~37ms delta over 10M iterations corresponds to nanosecond-level differences \nper call, which are statistically exploitable under controlled conditions.\n\n## Attack Scenario\n\n1. Attacker intercepts `authorization_code` via Custom URI Scheme Hijacking\n2. PKCE blocks token request \u2014 attacker lacks `code_verifier`\n3. Attacker sends repeated requests to `/token` endpoint measuring response times\n4. Using timing oracle, attacker recovers `code_verifier` character by character\n5. Attacker obtains Access Token \u2192 Account Takeover\n\n\u003e **Note:** Practical exploitability is limited due to the single-use nature of \n\u003e authorization codes and real-world network noise. However, the vulnerable \n\u003e pattern should be corrected as a defense-in-depth measure.\n\n## Recommended Fix\n\nReplace `==` with `hmac.compare_digest()` for constant-time comparison:\n\ncr: Elvin Latifli",
  "id": "BREW-ansible-CVE-2026-49265",
  "modified": "2026-10-02T08:50:21Z",
  "published": "2026-09-30T18:44:09Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/oauthlib/oauthlib/security/advisories/GHSA-xpv3-w29h-x7cv"
    },
    {
      "type": "WEB",
      "url": "https://github.com/oauthlib/oauthlib/pull/963"
    },
    {
      "type": "WEB",
      "url": "https://github.com/oauthlib/oauthlib/commit/40b0ab56da3682c2484a4b78bbff309f8025d950"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/oauthlib/oauthlib"
    }
  ],
  "schema_version": "1.7.3",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Oauthlib: Timing Attack Vulnerability in PKCE code_verifier Comparison (CWE-208)",
  "upstream": [
    "GHSA-xpv3-w29h-x7cv",
    "CVE-2026-49265",
    "PYSEC-2026-4114"
  ]
}

GHSA-XPV3-W29H-X7CV

Vulnerability from github – Published: 2026-09-29 17:56 – Updated: 2026-09-29 17:56

Summary

Oauthlib: Timing Attack Vulnerability in PKCE code_verifier Comparison (CWE-208)

Details

Summary

Affected Component

File: oauthlib/oauth2/rfc6749/grant_types/authorization_code.py
Functions: code_challenge_method_plain, code_challenge_method_s256
Vulnerability Type: CWE-208 (Observable Timing Discrepancy)

Technical Details

Python's == operator uses short-circuit evaluation when comparing strings: 1. Returns False immediately if lengths differ 2. Compares characters left-to-right, stopping at first mismatch

This means comparison time varies linearly with the length of the common prefix between the attacker-supplied verifier and the stored challenge, creating a measurable timing oracle.

Proof of Concept

Tested locally against oauthlib source (network jitter eliminated to isolate pure Python execution time):

Input	Result	Time (10M iterations)
Wrong first char (`B` + `A`*49)	Fast reject	0.34106s
49 chars correct (`A`*49 + `B`)	Deep compare	0.37847s
Difference		0.03741s

The ~37ms delta over 10M iterations corresponds to nanosecond-level differences per call, which are statistically exploitable under controlled conditions.

Attack Scenario

Attacker intercepts authorization_code via Custom URI Scheme Hijacking
PKCE blocks token request — attacker lacks code_verifier
Attacker sends repeated requests to /token endpoint measuring response times
Using timing oracle, attacker recovers code_verifier character by character
Attacker obtains Access Token → Account Takeover

Note: Practical exploitability is limited due to the single-use nature of authorization codes and real-world network noise. However, the vulnerable pattern should be corrected as a defense-in-depth measure.

Recommended Fix

Replace == with hmac.compare_digest() for constant-time comparison:

cr: Elvin Latifli

Severity

6.8 (Medium)


                  
                    CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "oauthlib"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "3.0.0"
            },
            {
              "fixed": "4.0.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-49265"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-208"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-09-29T17:56:31Z",
    "nvd_published_at": null,
    "severity": "MODERATE"
  },
  "details": "## Summary\n\nA timing side-channel vulnerability exists in the PKCE (RFC 7636) implementation \nof the Authorization Code Grant flow. The `code_challenge_method_plain` function \nuses Python\u0027s standard `==` operator for string comparison instead of a \nconstant-time comparison function, potentially allowing timing-based attacks.\n\n## Affected Component\n\n- File: `oauthlib/oauth2/rfc6749/grant_types/authorization_code.py`\n- Functions: `code_challenge_method_plain`, `code_challenge_method_s256`\n- Vulnerability Type: CWE-208 (Observable Timing Discrepancy)\n\n## Technical Details\n\nPython\u0027s `==` operator uses short-circuit evaluation when comparing strings:\n1. Returns `False` immediately if lengths differ\n2. Compares characters left-to-right, stopping at first mismatch\n\nThis means comparison time varies linearly with the length of the common prefix \nbetween the attacker-supplied verifier and the stored challenge, creating a \nmeasurable timing oracle.\n\n## Proof of Concept\n\nTested locally against oauthlib source (network jitter eliminated to isolate \npure Python execution time):\n\n| Input | Result | Time (10M iterations) |\n|---|---|---|\n| Wrong first char (`B` + `A`*49) | Fast reject | 0.34106s |\n| 49 chars correct (`A`*49 + `B`) | Deep compare | 0.37847s |\n| **Difference** | | **0.03741s** |\n\nThe ~37ms delta over 10M iterations corresponds to nanosecond-level differences \nper call, which are statistically exploitable under controlled conditions.\n\n## Attack Scenario\n\n1. Attacker intercepts `authorization_code` via Custom URI Scheme Hijacking\n2. PKCE blocks token request \u2014 attacker lacks `code_verifier`\n3. Attacker sends repeated requests to `/token` endpoint measuring response times\n4. Using timing oracle, attacker recovers `code_verifier` character by character\n5. Attacker obtains Access Token \u2192 Account Takeover\n\n\u003e **Note:** Practical exploitability is limited due to the single-use nature of \n\u003e authorization codes and real-world network noise. However, the vulnerable \n\u003e pattern should be corrected as a defense-in-depth measure.\n\n## Recommended Fix\n\nReplace `==` with `hmac.compare_digest()` for constant-time comparison:\n\ncr: Elvin Latifli",
  "id": "GHSA-xpv3-w29h-x7cv",
  "modified": "2026-09-29T17:56:31Z",
  "published": "2026-09-29T17:56:31Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/oauthlib/oauthlib/security/advisories/GHSA-xpv3-w29h-x7cv"
    },
    {
      "type": "WEB",
      "url": "https://github.com/oauthlib/oauthlib/pull/963"
    },
    {
      "type": "WEB",
      "url": "https://github.com/oauthlib/oauthlib/commit/40b0ab56da3682c2484a4b78bbff309f8025d950"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/oauthlib/oauthlib"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Oauthlib: Timing Attack Vulnerability in PKCE code_verifier Comparison (CWE-208)"
}

PYSEC-2026-4114

Vulnerability from pysec - Published: 2026-10-01 16:38 - Updated: 2026-10-01 17:10

Details

Summary

Affected Component

File: oauthlib/oauth2/rfc6749/grant_types/authorization_code.py
Functions: code_challenge_method_plain, code_challenge_method_s256
Vulnerability Type: CWE-208 (Observable Timing Discrepancy)

Technical Details

Python's == operator uses short-circuit evaluation when comparing strings: 1. Returns False immediately if lengths differ 2. Compares characters left-to-right, stopping at first mismatch

This means comparison time varies linearly with the length of the common prefix between the attacker-supplied verifier and the stored challenge, creating a measurable timing oracle.

Proof of Concept

Tested locally against oauthlib source (network jitter eliminated to isolate pure Python execution time):

Input	Result	Time (10M iterations)
Wrong first char (`B` + `A`*49)	Fast reject	0.34106s
49 chars correct (`A`*49 + `B`)	Deep compare	0.37847s
Difference		0.03741s

The ~37ms delta over 10M iterations corresponds to nanosecond-level differences per call, which are statistically exploitable under controlled conditions.

Attack Scenario

Attacker intercepts authorization_code via Custom URI Scheme Hijacking
PKCE blocks token request — attacker lacks code_verifier
Attacker sends repeated requests to /token endpoint measuring response times
Using timing oracle, attacker recovers code_verifier character by character
Attacker obtains Access Token → Account Takeover

Note: Practical exploitability is limited due to the single-use nature of authorization codes and real-world network noise. However, the vulnerable pattern should be corrected as a defense-in-depth measure.

Recommended Fix

Replace == with hmac.compare_digest() for constant-time comparison:

cr: Elvin Latifli

Severity

6.8 (Medium)


                  
                    CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N

Impacted products

Name	purl
oauthlib	pkg:pypi/oauthlib

Aliases

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "oauthlib",
        "purl": "pkg:pypi/oauthlib"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "3.0.0"
            },
            {
              "fixed": "4.0.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "3.0.0",
        "3.0.1",
        "3.0.2",
        "3.1.0",
        "3.1.1",
        "3.2.0",
        "3.2.1",
        "3.2.2",
        "3.3.0",
        "3.3.1"
      ]
    }
  ],
  "aliases": [
    "CVE-2026-49265",
    "GHSA-xpv3-w29h-x7cv"
  ],
  "details": "## Summary\n\nA timing side-channel vulnerability exists in the PKCE (RFC 7636) implementation \nof the Authorization Code Grant flow. The `code_challenge_method_plain` function \nuses Python\u0027s standard `==` operator for string comparison instead of a \nconstant-time comparison function, potentially allowing timing-based attacks.\n\n## Affected Component\n\n- File: `oauthlib/oauth2/rfc6749/grant_types/authorization_code.py`\n- Functions: `code_challenge_method_plain`, `code_challenge_method_s256`\n- Vulnerability Type: CWE-208 (Observable Timing Discrepancy)\n\n## Technical Details\n\nPython\u0027s `==` operator uses short-circuit evaluation when comparing strings:\n1. Returns `False` immediately if lengths differ\n2. Compares characters left-to-right, stopping at first mismatch\n\nThis means comparison time varies linearly with the length of the common prefix \nbetween the attacker-supplied verifier and the stored challenge, creating a \nmeasurable timing oracle.\n\n## Proof of Concept\n\nTested locally against oauthlib source (network jitter eliminated to isolate \npure Python execution time):\n\n| Input | Result | Time (10M iterations) |\n|---|---|---|\n| Wrong first char (`B` + `A`*49) | Fast reject | 0.34106s |\n| 49 chars correct (`A`*49 + `B`) | Deep compare | 0.37847s |\n| **Difference** | | **0.03741s** |\n\nThe ~37ms delta over 10M iterations corresponds to nanosecond-level differences \nper call, which are statistically exploitable under controlled conditions.\n\n## Attack Scenario\n\n1. Attacker intercepts `authorization_code` via Custom URI Scheme Hijacking\n2. PKCE blocks token request \u2014 attacker lacks `code_verifier`\n3. Attacker sends repeated requests to `/token` endpoint measuring response times\n4. Using timing oracle, attacker recovers `code_verifier` character by character\n5. Attacker obtains Access Token \u2192 Account Takeover\n\n\u003e **Note:** Practical exploitability is limited due to the single-use nature of \n\u003e authorization codes and real-world network noise. However, the vulnerable \n\u003e pattern should be corrected as a defense-in-depth measure.\n\n## Recommended Fix\n\nReplace `==` with `hmac.compare_digest()` for constant-time comparison:\n\ncr: Elvin Latifli",
  "id": "PYSEC-2026-4114",
  "modified": "2026-10-01T17:10:33.763932Z",
  "published": "2026-10-01T16:38:40.027560Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/oauthlib/oauthlib/security/advisories/GHSA-xpv3-w29h-x7cv"
    },
    {
      "type": "WEB",
      "url": "https://github.com/oauthlib/oauthlib/pull/963"
    },
    {
      "type": "WEB",
      "url": "https://github.com/oauthlib/oauthlib/commit/40b0ab56da3682c2484a4b78bbff309f8025d950"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/oauthlib/oauthlib"
    },
    {
      "type": "PACKAGE",
      "url": "https://pypi.org/project/oauthlib"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/advisories/GHSA-xpv3-w29h-x7cv"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-49265"
    }
  ],
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Oauthlib: Timing Attack Vulnerability in PKCE code_verifier Comparison (CWE-208)"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.

Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.

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BREW-ANSIBLE-CVE-2026-49265 (GHSA-XPV3-W29H-X7CV)

Summary

Affected Component

Technical Details

Proof of Concept

Attack Scenario

Recommended Fix

GHSA-XPV3-W29H-X7CV

Summary

Affected Component

Technical Details

Proof of Concept

Attack Scenario

Recommended Fix

PYSEC-2026-4114

Summary

Affected Component

Technical Details

Proof of Concept

Attack Scenario

Recommended Fix

Tags

Sightings

Nomenclature

Related by attack behaviour