CVE-2025-64527

Envoy crashes when JWT authentication is configured with the remote JWKS fetching, allow_missing_or_failed is enabled, multiple JWT tokens are present in the request headers and the JWKS fetch fails.

Details

This is caused by a re-entry bug in the JwksFetcherImpl. When the first token's JWKS fetch fails, onJwksError() callback triggers processing of the second token, which calls fetch() again on the same fetcher object.

The original callback's reset() then clears the second fetch's state (receiver_ and request_) which causes a crash when the async HTTP response arrives.

PoC

• allow_missing_or_failed or allow_missing is enabled
• The client send 2 Authorization headers
• the remote JWKS fetching failed
• There will be crash

Mitigation

• Disable the allow_missing_or_failed or allow_missing

DoS and Crash

The application dereferences a null pointer, causing a crash. Typical impact: denial of service via crash.

CVE-2025-64527 has a CVSS score of 6.5 (Medium). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.36.3, 1.35.7, 1.34.11, 1.33.13); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2025-64527? CVE-2025-64527 is a medium-severity null pointer dereference vulnerability in github.com/envoyproxy/envoy (go), affecting versions >= 1.36.0, <= 1.36.2. It is fixed in 1.36.3, 1.35.7, 1.34.11, 1.33.13. The application dereferences a null pointer, causing a crash.
2. How severe is CVE-2025-64527? CVE-2025-64527 has a CVSS score of 6.5 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of github.com/envoyproxy/envoy are affected by CVE-2025-64527? github.com/envoyproxy/envoy (go) versions >= 1.36.0, <= 1.36.2 is affected.
4. Is there a fix for CVE-2025-64527? Yes. CVE-2025-64527 is fixed in 1.36.3, 1.35.7, 1.34.11, 1.33.13. Upgrade to this version or later.
5. Is CVE-2025-64527 exploitable, and should I be worried? Whether CVE-2025-64527 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2025-64527 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2025-64527?
   • Upgrade github.com/envoyproxy/envoy to 1.36.3 or later
   • Upgrade github.com/envoyproxy/envoy to 1.35.7 or later
   • Upgrade github.com/envoyproxy/envoy to 1.34.11 or later
   • Upgrade github.com/envoyproxy/envoy to 1.33.13 or later