PyJWT: ReDoS vulnerability when calling the is_pem_format function.

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

4.4 · CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H

EPSS

• CVE-2026-102270: 0.25% estimated exploitation activity in the next 30 days; percentile 15.89 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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 Impact The attacker could use extensive resources, which could make the resource (e.g. a web server) unavailable. Maintainer update (2026-09-10): We reproduced the reported quadratic regex behavior on…

Published by the source

30 Sep 2026, 14:40 UTC

Last modified by the source

1 Oct 2026, 17:55 UTC

Source last checked

26 Oct 2026, 13:54 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-jwrc-g2q2-pq5p

2. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-jwrc-g2q2-pq5p

3. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-jwrc-g2q2-pq5p

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# Patch Next advisory brief: CVE-2026-102270

Advisory: PyJWT: ReDoS vulnerability when calling the `is_pem_format` function.
IDs: CVE-2026-102270, GHSA-jwrc-g2q2-pq5p
Record: https://patchnext.com/advisories/cve-2026-102270 (revision 3, source checked 26 Oct 2026, 13:54 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 4.4)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: pyjwt 2.14.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI pyjwt: affected <= 2.13.0; fixed in 2.14.0

## Suggested inspection (read-only)
- `python -m pip show pyjwt`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on pyjwt.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-jwrc-g2q2-pq5p (GitHub-reviewed advisory GHSA-jwrc-g2q2-pq5p lists affected ranges: PyPI pyjwt >=0 <=2.13.0)
- Verified: https://osv.dev/vulnerability/GHSA-jwrc-g2q2-pq5p (OSV record GHSA-jwrc-g2q2-pq5p lists affected ranges: PyPI pyjwt >=0 <2.14.0 (fixed))

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