CVE-2026-62995: low-severity vulnerability in authlib joserfc
joserfc accepts JWT with padding, leading to JWT malleability
Published · Updated
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8Vexday Risk Score
No sign of exploitation. No public exploitation artifact known so far.
ssvc Trackcvss 2.3epss 0.1%
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.
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
Affected products
authlib · joserfcRelated CVEs — authlib joserfc
In the same product, most dangerous first.
CVE-2026-27932HIGHjoserfc PBES2 p2c Unbounded Iteration Count enables Denial of Service (DoS)EPSS 0.5%CVE-2025-65015CRITICALjoserfc has Possible Uncontrolled Resource Consumption Vulnerability Triggered by Logging Arbitrarily Large JWT Token PayloadsEPSS 0.4%CVE-2026-48990MEDIUMjoserfc: b64=false RFC7797 JWS payloads bypass JWSRegistry payload-size limits during deserializationEPSS 0.2%CVE-2026-119283HIGHjoserfc: Unbounded JWE General JSON `recipients` Array Leads to CPU Exhaustion (DoS) via Repeated RSA Private-Key DecryptionEPSS 0.2%CVE-2026-119284MEDIUMjoserfc: Compact JWS size guard allocates attacker-controlled segments before rejectionEPSS 0.2%CVE-2026-49852HIGHjoserfc: HS256/HS384/HS512 verify accepts empty/nil HMAC key (cross-language sibling of CVE-2026-45363)EPSS 0.2%