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CVE-2026-48521

5.9 · MEDIUM

Envoy is an open source edge and service proxy designed for cloud-native applications.

Published Sep 21, 2026envoyproxyCWE-476EPSS 0.74%

Overview

CVE-2026-48521 is a medium-severity vulnerability affecting envoyproxy envoy. It was published on September 21, 2026 and has a CVSS 3.1 base score of 5.9 (MEDIUM).

This vulnerability has a CVSS 3.1 base score of 5.9, rated MEDIUM. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

Technical description

Envoy is an open source edge and service proxy designed for cloud-native applications. Prior to 1.36.10, 1.37.6, 1.38.4, and 1.39.1, Envoy's ProdClusterManagerFactory::allocateConnPool dereferences transport_socket_options while selecting an HTTP/3 connection pool without first checking whether the pointer is null. LoadBalancerContext implementations used by synthetic, mirror, health-check, and async-client calls can return no transport-socket options. With auto_config and HTTP/3 enabled, routine traffic reaching one of those contexts can crash an Envoy worker. The relevant scope boundary is that the affected branch requires HTTP/3 in the protocol set and a context that supplies no transport-socket options. This issue is fixed in versions 1.36.10, 1.37.6, 1.38.4, and 1.39.1.

Remediation

Check the references section for vendor advisories and patches from envoyproxy. Update envoy to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

Affected products

VendorProductVersionsStatus
envoyproxyenvoy>= 0, < 1.36.10Affected

References

GitHubgithub.com/envoyproxy/envoy/commit/8ef2da8527fcd17388b046c1add4fb47fb5d0868GitHubgithub.com/envoyproxy/envoy/commit/cec4899acf03cf551f28611a5f32385648d95f96GitHubgithub.com/envoyproxy/envoy/commit/e7b4839beef7f43594ce8e94c4563c80db04a8a7GitHubgithub.com/envoyproxy/envoy/commit/f5436f44103fb14cb8ba42a8db0f54a06c98c45aGitHubgithub.com/envoyproxy/envoy/releases/tag/v1.36.10GitHubgithub.com/envoyproxy/envoy/releases/tag/v1.37.6GitHubgithub.com/envoyproxy/envoy/releases/tag/v1.38.4GitHubgithub.com/envoyproxy/envoy/releases/tag/v1.39.1GitHubgithub.com/envoyproxy/envoy/security/advisories/GHSA-5vff-j9p4-38j3GitHubgithub.com/envoyproxy/envoy/security/advisories/GHSA-5vff-j9p4-38j3

How CyberStrike helps

Frequently asked questions

What is CVE-2026-48521?

CVE-2026-48521 is a medium-severity vulnerability affecting envoyproxy envoy. It was published on September 21, 2026 and has a CVSS 3.1 base score of 5.9 (MEDIUM).

How severe is CVE-2026-48521?

This vulnerability has a CVSS 3.1 base score of 5.9, rated MEDIUM. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

How do I fix or remediate CVE-2026-48521?

Check the references section for vendor advisories and patches from envoyproxy. Update envoy to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

How can CyberStrike help with CVE-2026-48521?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2026-48521 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.

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