CVE-2026-47221: Envoy: Null pointer deref in internal redirects

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2026-06-26 · updated 2026-10-25
Weakness: CWE-476

Description

Envoy is an open source edge and service proxy designed for cloud-native applications. From 1.18.0 until 1.35.13, 1.36.9, 1.37.5, and 1.38.3, the router filter contains a null pointer dereference vulnerability when handling HTTP 303 (See Other) internal redirects for body-less non-GET/HEAD requests. When a POST, PUT, DELETE, or PATCH request without a body is sent to a route configured with internal redirect policy that includes 303 in redirect_response_codes, and the upstream responds with HTTP 303, the redirect handling code attempts to drain a request body buffer that was never allocated. This results in a segmentation fault that crashes the entire Envoy process. When route configured with internal_redirect_policy including 303 in redirect_response_codes and upstream must return HTTP 303 response, an unauthenticated attacker can exploit this to cause complete denial of service, terminating all active connections. This vulnerability is fixed in 1.35.13, 1.36.9, 1.37.5, and 1.38.3.

Affected products

envoyproxy envoy: from 1.18.0 before 1.35.13; from 1.36.0 before 1.36.9; from 1.37.0 before 1.37.5; from 1.38.0 before 1.38.3 — fixed in 1.35.13, 1.36.9, 1.37.5, 1.38.3

How to fix

Upgrade to a fixed version: envoyproxy envoy 1.35.13, 1.36.9, 1.37.5, 1.38.3. Check the vendor advisory for mitigations.

References

Get alerted when CVE-2026-47221 or the next vulnerability affects your stack