PyJWT is a Python implementation of JSON Web Token standards.
CVE-2026-102270
Summary There is a Re-DoS vulnerability in the ispemformat function which results in a intesive CPU usage if an attacker is been able to provide a custom certificate. Details The problem is that the lazy quantifier .+? will always first try to match as little as possible until it finds a ---- END. Normally this means the complexity of this should be O(N). However, by providing an input which consists only of ----BEGIN CERTIFICATE----- lines and no ---- END line, the regex algorithm will first try to match the first line and then, with the lazy quantifier, all the lines until the end O(N), which then fails since it is unable to find a ---- END line. It will then jump to the next line, resulting in N re-scans of the whole string, which means the complexity basically results in O(N²). PoC python import time import re BEGINLINE = b"-----BEGIN CERTIFICATE-----\n" PEMS = { b"CERTIFICATE", b"TRUSTED CERTIFICATE", b"PRIVATE KEY", b"PUBLIC KEY", b"ENCRYPTED PRIVATE KEY", b"OPENSSH PRIVATE KEY", b"DSA PRIVATE KEY", b"RSA PRIVATE KEY", b"RSA PUBLIC KEY", b"EC PRIVATE KEY", b"DH PARAMETERS", b"NEW CERTIFICATE REQUEST", b"CERTIFICATE REQUEST", b"SSH2 PUBLIC KEY", b"SSH2 ENCRYPTED PRIVATE KEY",…
Assessment
- CVSS
- 4.9 (v3.1)
- Severity
- Medium
- EPSS
- 0.25% chance of exploitation in the next 30 days
- Known exploited
- Not listed in CISA KEV
- Exploit availability
- Nothing found in Exploit-DB, Metasploit, Nuclei or public PoC repositories
- Published
- 28 September 2026
- Last updated
- 6 October 2026
- Weakness
- CWE-1333
- Assigner
- security-advisories@github.com
CVSS vectorCVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H
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-jwrc-g2q2-pq5p
- https://nvd.nist.gov/vuln/detail/CVE-2026-102270
- https://github.com/advisories/GHSA-jwrc-g2q2-pq5p
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