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Security Advisories

CVE-2026-48525

NVD

https://nvd.nist.gov/vuln/detail/CVE-2026-48525

Severity

5.3

Medium

CVSS V3

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Summary

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

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.

References

  • https://nvd.nist.gov/vuln/detail/CVE-2026-48525
  • https://github.com/advisories/GHSA-w7vc-732c-9m39
  • https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/48xxx/CVE-2026-48525.json
  • https://github.com/jpadilla/pyjwt/security/advisories/GHSA-w7vc-732c-9m39

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