PyJWT BOM Bypass

Exploitation

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

CVSS

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

EPSS

• CVE-2026-102272: 0.22% estimated exploitation activity in the next 30 days; percentile 12.18 (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.

Affected Package - Package: PyJWT (pyjwt on PyPI) - Repository: https://www.google.com/url?q=https://github.com/jpadilla/pyjwt&source=gmail&ust=1781794518474000&sa=E - Affected version: 2.13.0 - Vulnerability class: Algorithm confusion / patch bypass --- Root Cause PyJWT 2.13.0 introduced a guard in HMACAlgorithm.preparekey() (file jwt/algorithms.py, approximately line 344) to prevent RSA public key material from being used as an HMAC secret — the root cause of CVE-2026-48526. The guard uses bytes.lstrip() before calling startswith(b"{"): bytes.lstrip() with no argument removes only bytes in the ASCII whitespace set (\x20 \t \n \r \x0b \x0c). A UTF-8 BOM prefix (\xef\xbb\xbf) is not stripped, so stripped.startswith(b"{") returns False for any BOM-prefixed JWK JSON. The JWK detection block is never entered, and the RSA public key bytes are silently accepted as the HMAC-SHA256 secret. --- PoC Sketch (pseudocode — not a weaponized payload) --- Impact An unauthenticated network attacker…

Published by the source

29 Sep 2026, 23:14 UTC

Last modified by the source

1 Oct 2026, 17:56 UTC

Source last checked

26 Oct 2026, 13:54 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-r6x4-923q-g947

2. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-r6x4-923q-g947

3. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-r6x4-923q-g947

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# Patch Next advisory brief: CVE-2026-102272

Advisory: PyJWT BOM Bypass
IDs: CVE-2026-102272, GHSA-r6x4-923q-g947
Record: https://patchnext.com/advisories/cve-2026-102272 (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: High (CVSS 7.4)
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, <= 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-r6x4-923q-g947 (GitHub-reviewed advisory GHSA-r6x4-923q-g947 lists affected ranges: PyPI pyjwt >=2.13.0 <=2.13.0)
- Verified: https://osv.dev/vulnerability/GHSA-r6x4-923q-g947 (OSV record GHSA-r6x4-923q-g947 lists affected ranges: PyPI pyjwt >=2.13.0 <2.14.0 (fixed))

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