CVE-2026-102267: PyJWT: PyJWKClient follows redirects when fetching JWKS
Summary
PyJWT 2.13.0 PyJWKClient followed HTTP redirects while fetching a JWKS, without validating the redirect destination. A configured trusted endpoint could therefore redirect the client to a different host.
Impact
When an application uses PyJWKClient with caller-supplied request headers and an attacker can influence the configured endpoint's response, the redirected request could expose those headers and the redirected response could be used as authoritative key material. This could cause JWKS trust poisoning and, in affected mixed-configuration applications, forged JWT acceptance. The issue requires an attacker-influenced redirect from the configured JWKS endpoint; it is not triggered by a token kid alone.
Affected versions
PyJWT <= 2.13.0.
Fix
The issue is fixed on master in commit 0a795b8e1f6ef08f634aa7086fc41cc6d5ce3e56. PyJWKClient now disables automatic redirects for JWKS fetches. Regression tests verify that a redirect is rejected without contacting its destination, while normal fetches, headers, caching, errors, timeouts, and SSL context remain covered.
The fix is present in the unreleased development branch. The patched version will be recorded after a released PyJWT 2.x version containing the fix is confirmed.
Credit
Credit: the original reporter of GHSA-9v7f-9g4p-ffgj. Additional redirect header-leak and cache-poisoning evidence from the newer duplicate report GHSA-43g3-98cx-x446 is preserved in the duplicate record and informed this canonical advisory update.
Maintainer update — 2026-09-11
The verified fix for this advisory is included in PyJWT 2.14.0, released on 2026-09-11 and available on PyPI. PyJWT 2.14.0 is the first release containing the fix. This advisory is now published with 2.14.0 recorded as the patched version.
Other sources
PyJWT is a Python implementation of JSON Web Token standards. Prior to 2.14.0, PyJWT PyJWKClient is affected because redirect destinations are not revalidated against the JWKS trust boundary. This occurs when a configured trusted JWKS endpoint returns an attacker-influenced redirect. As a result, PyJWKClient follows the redirect and consumes the redirected response as key material. Consequently, forwarded credentials may be disclosed or verification keys may be substituted. This issue is fixed in version 2.14.0.
— MITRE
PyJWT: PyJWKClient follows redirects when fetching JWKS
— Microsoft
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
pip/PyJWTto a version that resolves this vulnerability.Fixed in 2.14.0 - Upgrade
Upgrade to a fixed release to a version that resolves this vulnerability.
Fixed in 2.15.1-1 - Upgrade
Upgrade
debian/pyjwtto a version that resolves this vulnerability.Fixed in 2.15.1-1 - Upgrade
Upgrade
PyJWTto a version that resolves this vulnerability.Fixed in 2.14.0
Event History
Frequently Asked Questions
Which deployments are exposed to this issue?
Deployments using PyJWT PyJWKClient before version 2.14.0 are affected when they fetch keys from a configured trusted JWKS endpoint that can return an attacker-influenced redirect.
What does an attacker need to exploit it?
An attacker needs influence over a redirect returned by the configured JWKS endpoint. PyJWKClient then follows the redirect without revalidating the destination against the JWKS trust boundary.
What is the impact of a successful exploit?
Forwarded credentials may be disclosed to the redirect destination, or the redirected response may be consumed as key material, allowing verification keys to be substituted.
What is the available remediation?
Upgrade PyJWT to version 2.14.0, which fixes the redirect handling issue.