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CVE-2026-49265— OAuthLib: Timing Attack Vulnerability in PKCE code_verifier Comparison

Quick assessment

Affected
oauthlib oauthlib
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

OAuthLib 是用于 Python 3.6+ 的 OAuth 请求签名逻辑的实现。从版本 3.0.0 到 4.0.0，OAuthLib 在 中对 PKCE（Proof Key for Code Exchange）的检查，在 和 函数中，使用普通字符串相等性运算符来比较攻击者提供的 值与存储的挑战值。由于该比较可能在检测到长度差异或首个不匹配字符时就提前返回，通过反复测量令牌端点的响应时间，可以获取有关共同前缀的时序信息，从而可能用于恢复 、非法获取访问令牌，以及接管用户账户。 实际利用需要拦截一个一次性的授权码

CVSS 6.8 · Medium EPSS 0.38% · P30

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application

Affected Version Matrix 1

VendorProduct Version RangeStatus
oauthlib oauthlib >= 3.0.0, < 4.0.0 affected
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I. Basic Information for CVE-2026-49265

Vulnerability Information
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Vulnerability Title
OAuthLib: Timing Attack Vulnerability in PKCE code_verifier Comparison
Source: CVE Program / CVE List V5
Vulnerability Description
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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
通过时间差异性导致的信息暴露
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
oauthlib oauthlib >= 3.0.0, < 4.0.0 -

II. Public POCs for CVE-2026-49265

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III. Intelligence Information for CVE-2026-49265

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Patches & Fixes for CVE-2026-49265 (2)

Vendor Advisories for CVE-2026-49265 (2)

Other References for CVE-2026-49265 (1)

IV. Related Vulnerabilities

Same product: oauthlib
Same vendor: oauthlib
Same weakness: CWE-208

V. Comments for CVE-2026-49265

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