CVE-2026-62995
LowCVSS 2.3Exploitation Probability (EPSS)
Low risk1th percentile - higher than 1% of all known CVEs
Summary
The Python library joserfc versions 1.7.1 and earlier accept JWTs with trailing padding (==), which is non-conforming to JOSE specifications. This leads to token malleability, potentially allowing bypass of token revocation or anti-replay protection.
Risk Assessment
The organization may face compromised JWT integrity, enabling attackers to bypass token deny lists and anti-replay mechanisms, potentially leading to unauthorized access.
Recommendation
Immediately upgrade joserfc to version 1.7.2 or later, which includes a fix for this vulnerability.
Other vulnerabilities in joserfc
See all- CVE-2026-75509Medium
joserfc, a Python library implementing JOSE standards, prior to version 1.7.3, has a vulnerability in JWTClaimsRegistry that applies membership matching to list-valued iss and sub claims, allowing an array-valued iss containing the expected issuer to pass an intended equality check and enabling issuer-validation bypass.
- CVE-2026-49852High
Vulnerability in the joserfc Python library before version 1.6.8 allows an attacker to forge HMAC tokens when the verification key is an empty string or None. The library does not reject zero-length keys, allowing signature verification bypass.
- CVE-2026-48990Medium
The joserfc library in versions 1.3.4 through 1.6.5 accepts oversized JWS payloads without proper length checks, potentially leading to resource exhaustion. This issue has been fixed in version 1.6.7.
Original NVD description (English source)
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.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS