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Advisory record · GHSA-42vr-xj54-vc7v

PyJWT: Unauthenticated RecursionError DoS in pre-verification payload parse (PyJWKClient.get_signing_key_from_jwt / verify_signature=False)

CVSS 5.3 MediumEPSS 0.0041 · 35th percentile

Published by the GitHub Advisory Database at 30 Sept 2026, 15:41 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

PackageEcosystemAffectedFixed in
pyjwtPyPI>=2.0.0a1, <2.15.02.15.0
Identifiers
GHSA-42vr-xj54-vc7v · CVE-2026-101918 · PYSEC-2026-4141
Weakness (CWE)
CWE-248
Tags
Published
30 Sept 2026
Updated
1 Oct 2026

Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

PyJWT versions from 2.0.0a1 before 2.15.0 are affected. When a token is decoded with signature verification turned off, or passed to `PyJWKClient.get_signing_key_from_jwt`, an unauthenticated attacker can send a token whose payload is deeply nested JSON. This raises an uncaught `RecursionError` instead of a PyJWT error, so the calling request fails with an unhandled exception. Upgrade to PyJWT 2.15.0.

Written 1 Nov 2026.

Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

Severity and exploitation

ScoreRatingCVSSVectorSource
5.3 Medium 3.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L CNA (GitHub_M)
  • CISA KEV Not listed.
  • EPSS 0.0041, the 35th percentile, on 5 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

  1. 31 Oct 2026, 14:09 UTC First seen by agentprime
  2. 31 Oct 2026, 14:09 UTC Confirmed by OSV

Sources

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.