Amazon Linux 2023 Security Advisory: ALAS2023-2026-2051
Advisory Released Date: 2026-08-17
Advisory Updated Date: 2026-08-17
PyJWT is a JSON Web Token implementation in Python. Prior to 2.13.0, PyJWKClient passes its uri argument directly to urllib.request.urlopen() which uses Python stdlib's default OpenerDirector registering HTTPHandler, HTTPSHandler, FTPHandler, FileHandler, and DataHandler. There is currently no documented option to restrict which schemes PyJWKClient will fetch. If an application's jku URL ingestion path accepts attacker-influenced URLs (e.g., from JWT header, configuration file, OAuth flow parameter), the attacker can cause PyJWKClient to read arbitrary local files via file:// (SSRF on local filesystem), cause PyJWKClient to attempt FTP / data-URI fetches (broader SSRF surface), or forge tokens that PyJWT verifies as valid. The library does not directly return non-HTTP(S) URI contents to the attacker; the chained "plant a JWKS to forge tokens" scenario described in the original report requires additional application-layer flaws (attacker write access to a filesystem path, untrusted jku derivation) that this fix does not address. This vulnerability is fixed in 2.13.0. (CVE-2026-48522)
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. (CVE-2026-48525)
Affected Packages:
python-jwt
Issue Correction:
Run dnf update python-jwt --releasever 2023.12.20260817 or dnf update --advisory ALAS2023-2026-2051 --releasever 2023.12.20260817 to update your system.
More information on how to update your system can be found on this page: Amazon Linux 2023 documentation
noarch:
python3-jwt+crypto-2.4.0-1.amzn2023.0.5.noarch
python3-jwt-2.4.0-1.amzn2023.0.5.noarch
src:
python-jwt-2.4.0-1.amzn2023.0.5.src