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Envoy: Race condition in Dynamic Forward Proxy leads to use-after-free and segmentation faults

High severity GitHub Reviewed Published Sep 2, 2025 in envoyproxy/envoy • Updated Sep 15, 2025

Package

gomod github.com/envoyproxy/envoy (Go)

Affected versions

= 1.35.0
>= 1.34.0, < 1.34.5

Patched versions

1.35.1
1.34.5

Description

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) ([email protected])

References

@phlax phlax published to envoyproxy/envoy Sep 2, 2025
Published by the National Vulnerability Database Sep 3, 2025
Published to the GitHub Advisory Database Sep 15, 2025
Reviewed Sep 15, 2025
Last updated Sep 15, 2025

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(0th percentile)

Weaknesses

Use After Free

Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code. Learn more on MITRE.

CVE ID

CVE-2025-54588

GHSA ID

GHSA-g9vw-6pvx-7gmw

Source code

Credits

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