PyJWT is a Python implementation of JSON Web Token standards.
CVE-2026-102268
Prerequisites (both conditions must hold; both are deployment properties, not attacker-controlled at request time): The jwt.decode allow-list mixes an HMAC algorithm with an asymmetric one, e.g. algorithms=["ES256", "HS256"] (the RFC 8725 footgun the guard exists to backstop). The verification key is passed as raw PEM text/bytes on the non-PyJWK path, in a byte-form that cryptography's loader accepts but PyJWT's ispemformat regex does not recognize (marker-adjacent whitespace/indentation, CR-only line terminators, or the PEM folded to a single line). Such forms arise naturally from an indented YAML/JSON block, a single-line environment variable or JSON string, or a CR/LF round-trip through config tooling. The attacker additionally needs the public verification key, which is public by definition, and cryptography must be installed. The fix for CVE-2022-29217 rejects an asymmetric key handed to an HMAC algorithm, but only when ispemformat() recognizes the key as PEM. That recognizer accepts strictly fewer byte-forms than the loader that later parses the key, so a PEM the guard misses still loads as a valid public key and is then used as an HMAC secret. This is an incomplete-guard…
Proof-of-concept code is published
Public PoC
- Public PoCcovepseng/cve-2026-102268-poc
Signals come from Exploit-DB, Metasploit, Nuclei and published proof-of-concept repositories. Their absence means nothing was found, not that nothing exists.
Assessment
- CVSS
- 9.1 (v3.1)
- Severity
- Critical
- EPSS
- 0.24% chance of exploitation in the next 30 days
- Known exploited
- Not listed in CISA KEV
- Exploit availability
- Public PoC
- Published
- 28 September 2026
- Last updated
- 7 October 2026
- Weakness
- CWE-347
- Assigner
- security-advisories@github.com
CVSS vectorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
At the source
References
- https://github.com/jpadilla/pyjwt/commit/8b4e233a22206b34ec1186e912e75c0b2396ac07
- https://github.com/jpadilla/pyjwt/releases/tag/2.14.0
- https://github.com/jpadilla/pyjwt/security/advisories/GHSA-ffc3-869f-jxw9
- https://nvd.nist.gov/vuln/detail/CVE-2026-102268
- https://github.com/advisories/GHSA-ffc3-869f-jxw9
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