Vulnerability · Published May 28, 2026 · Assigned by GitHub_M
CVE-2026-48525PyJWT: Unauthenticated DoS via unbounded Base64URL decoding of unused payload segment in b64=false detached JWS
Medium 5.3
In plain English
A medium-severity uncontrolled resource consumption in pyjwt from jpadilla. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 31% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
PyJWT is a JSON Web Token implementation in Python. From 2.8.0 to 2.12.1, 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 detached_payload. 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. This vulnerability is fixed in 2.13.0.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | pyjwt | no fix listed | DEBIAN-CVE-2026-48525 |
| Debian:13 | pyjwt | no fix listed | DEBIAN-CVE-2026-48525 |
| Debian:14 | pyjwt | 2.13.0-1 | DEBIAN-CVE-2026-48525 |
| PyPI | pyjwt | 2.13.0 | GHSA-w7vc-732c-9m39 |
| PyPI | pyjwt | 2.13.0 | PYSEC-2026-178 |
| Ubuntu:22.04:LTS | pyjwt | 2.3.0-1ubuntu0.4 | USN-8823-1 |
| Ubuntu:24.04:LTS | pyjwt | 2.7.0-1ubuntu0.2 | USN-8823-1 |
| Ubuntu:24.04:LTS | pyjwt | 2.7.0-1ubuntu0.2 | UBUNTU-CVE-2026-48525 |
| Ubuntu:25.10 | pyjwt | no fix listed | UBUNTU-CVE-2026-48525 |
| Ubuntu:26.04:LTS | pyjwt | 2.10.1-4ubuntu1.1 | USN-8823-1 |
| Ubuntu:26.04:LTS | pyjwt | 2.10.1-4ubuntu1.1 | UBUNTU-CVE-2026-48525 |
Affected products (as reported)
Weakness: CWE-400 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
References
- https://github.com/jpadilla/pyjwt/security/advisories/GHSA-w7vc-732c-9m39 x_refsource_CONFIRM