CVE-2025-62409: Envoy allows large requests and responses to cause TCP connection pool crash

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.5% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2025-10-16 · updated 2026-10-09
Weakness: CWE-476

Description

Envoy is a cloud-native, open source edge and service proxy. Prior to 1.36.1, 1.35.5, 1.34.9, and 1.33.10, large requests and responses can potentially trigger TCP connection pool crashes due to flow control management in Envoy. It will happen when the connection is closing but upstream data is still coming, resulting in a buffer watermark callback nullptr reference. The vulnerability impacts TCP proxy and HTTP 1 & 2 mixed use cases based on ALPN. This vulnerability is fixed in 1.36.1, 1.35.5, 1.34.9, and 1.33.10.

Affected products

envoyproxy envoy: before 1.33.11; from 1.34.0 before 1.34.9; from 1.35.0 before 1.35.5; 1.36.0 — fixed in 1.33.11, 1.34.9, 1.35.5

How to fix

Upgrade to a fixed version: envoyproxy envoy 1.33.11, 1.34.9, 1.35.5. Check the vendor advisory for mitigations.

References

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