PyJWT: Unauthenticated DoS via unbounded Base64URL decoding of unused payload segment in b64=false detached JWS

Exploitation

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

CVSS

5.3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

EPSS

• CVE-2026-48525: 0.37% estimated exploitation activity in the next 30 days; percentile 31.01 (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.

[!NOTE] Practical impact depends on whether request body-size limits are enforced upstream (proxy/web-server/framework). Deployments with typical body-size caps (≤2 MB) bound the amplifier significantly; deployments accepting larger token inputs are more exposed. When verifying detached JWS tokens using the unencoded-payload option ("b64": false, RFC 7797), PyJWT performs Base64URL decoding of the compact-serialization payload segment before enforcing the detached-payload rules. For b64=false, PyJWT later discards that decoded payload and replaces it with the caller-provided detachedpayload. In practice, this turns the middle segment into an attacker-controlled “work amplifier”: a remote client can supply an arbitrarily large Base64URL payload segment that forces CPU work + memory allocations even if the signature is invalid. This creates an unauthenticated DoS vector against any endpoint that verifies detached JWS using PyJWT. --- Affected Component(s) jwt/apijws.py PyJWS.decode() /…

Published by the source

15 Jun 2026, 19:29 UTC

Last modified by the source

10 Sep 2026, 03:50 UTC

Source last checked

26 Oct 2026, 13:45 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-w7vc-732c-9m39

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-w7vc-732c-9m39

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# Patch Next advisory brief: CVE-2026-48525

Advisory: PyJWT: Unauthenticated DoS via unbounded Base64URL decoding of unused payload segment in b64=false detached JWS
IDs: CVE-2026-48525, GHSA-w7vc-732c-9m39
Record: https://patchnext.com/advisories/cve-2026-48525 (revision 2, source checked 26 Oct 2026, 13:45 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: pyjwt 2.13.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI pyjwt: affected >= 2.8.0, <= 2.12.1; fixed in 2.13.0

## 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://osv.dev/vulnerability/GHSA-w7vc-732c-9m39 (OSV record GHSA-w7vc-732c-9m39 lists affected ranges: PyPI pyjwt >=2.8.0 <2.13.0 (fixed))
- Verified: https://github.com/advisories/GHSA-w7vc-732c-9m39 (GitHub-reviewed advisory GHSA-w7vc-732c-9m39 lists affected ranges: PyPI pyjwt >=2.8.0 <=2.12.1)

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