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CVE-2026-62995— joserfc accepts JWT with padding, leading to JWT malleability

Quick assessment

Affected
authlib joserfc
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.

Authlib joserfc是Authlib组织开源的一个 Python 库，全面实现了 JOSE（JSON Object Signing and Encryption）系列标准，包括 JWS、JWE、JWK、JWT 等 RFC 规范，用于安全地处理 JSON 数据的签名与加密。 Authlib joserfc 1.7.2之前版本存在输入验证错误漏洞，该漏洞源于接受带有尾部填充(==)的JWT，不符合JOSE规范，可能导致绕过令牌撤销或防重放保护。

CVSS 2.3 · Low EPSS 0.14% · P3

Possible ATT&CK Techniques 1 AI

T1550.004 · Web Session Cookie

Affected Version Matrix 1

VendorProduct Version RangeStatus
authlib joserfc < 1.7.2 affected
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I. Basic Information for CVE-2026-62995

Vulnerability Information
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Vulnerability Title
joserfc accepts JWT with padding, leading to JWT malleability
Source: CVE Program / CVE List V5
Vulnerability Description
joserfc is a Python library that provides an implementation of several JSON Object Signing and Encryption (JOSE) standards. in versions 1.7.1 and prior, joserfc accepts JWTs with trailing padding (==) which are not conforming to the JOSE specifications. This leads to malleability of the JWTs when consumed by joserfc. Depending on this application this might or not be an issue. This could lead to bypass of token revocation or anti-replay protection when implemented as a deny list of tokens or a deny list of token hashes. Note that ECDSA JWS are always malleable because of the malleability of ECDSA signatures (first test case in the code bellow). This makes a scheme which assumes that JWTs are not malleable brittle. However for other signatures (or MAC) schemes it might make sense to assume non malleability of the token. This issue has been fixed in version 1.7.2.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N
Source: CVE Program / CVE List V5
Vulnerability Type
对数据真实性的验证不充分
Source: CVE Program / CVE List V5
Vulnerability Title
Authlib joserfc 输入验证错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Authlib joserfc是Authlib组织开源的一个 Python 库，全面实现了 JOSE（JSON Object Signing and Encryption）系列标准，包括 JWS、JWE、JWK、JWT 等 RFC 规范，用于安全地处理 JSON 数据的签名与加密。 Authlib joserfc 1.7.2之前版本存在输入验证错误漏洞，该漏洞源于接受带有尾部填充(==)的JWT，不符合JOSE规范，可能导致绕过令牌撤销或防重放保护。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
authlib joserfc < 1.7.2 -

II. Public POCs for CVE-2026-62995

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III. Intelligence Information for CVE-2026-62995

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Vendor Advisories for CVE-2026-62995 (1)

IV. Related Vulnerabilities

Same product: joserfc
Same vendor: authlib
Same weakness: CWE-345

V. Comments for CVE-2026-62995

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