GHSA-g9vw-6pvx-7gmw: Envoy: Race condition in Dynamic Forward Proxy leads to use-after-free and segmentation faults

Summary

A use-after-free (UAF) vulnerability in Envoy’s DNS cache causes abnormal process termination. Envoy may reallocate memory when processing a pending DNS resolution, causing list iterator to reference freed memory.

Details

The vulnerability exists in Envoy’s Dynamic Forward Proxy implementation starting from version v1.34.0. The issue occurs when a completion callback for a DNS resolution triggers new DNS resolutions or removes existing pending resolutions. This condition may occur in the following configuration:

1. Dynamic Forwarding Filter is enabled.
2. envoy.reloadable_features.dfp_cluster_resolves_hosts runtime flag is enabled.
3. The Host header is modified between the Dynamic Forwarding Filter and Router filters.

Impact

Denial of service due to abnormal process termination.

Attack vector(s)

Request to Envoy configured as indicated above.

Patches

Users should upgrade to v1.35.1 or v1.34.5.

Workaround

Set the envoy.reloadable_features.dfp_cluster_resolves_hosts runtime flag to false.

Detection

Abnormal process termination with the Envoy::Event::DispatcherImpl::runPostCallbacks() frame in the call stack.

Credits

Rohit Agrawal (agrawroh) (rohit.agrawal@databricks.com)

References

• GHSA-g9vw-6pvx-7gmw
• https://nvd.nist.gov/vuln/detail/CVE-2025-54588
• https://github.com/envoyproxy/envoy/releases/tag/v1.34.5
• https://github.com/envoyproxy/envoy/releases/tag/v1.35.1