CVE-2026-47221: Envoy null pointer dereference in router filter internal redirects

CVE-2026-47221 · Severity: medium · CVSS 5.9 · Published 2026-06-26

Envoy, a widely used service proxy for managing cloud-native network traffic, is vulnerable to a flaw that can cause the entire service to crash. An attacker can trigger this by sending a specific type of web request (such as a POST request without a body) that is redirected by a backend server. This results in a complete denial of service, terminating all active connections and disrupting application availability.

Technologies: Envoy Proxy Envoy. Vendors: Envoy Proxy.

Quick answers

Is CVE-2026-47221 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-47221 being exploited in the wild.
How severe is CVE-2026-47221?
Medium severity, with a CVSS score of 5.9, published 26 June 2026.
Which products and versions are affected?
Envoy Proxy Envoy 1.18.0 to 1.35.12, 1.36.0 to 1.36.8, 1.37.0 to 1.37.4, 1.38.0 to 1.38.2.
Is there a fix for CVE-2026-47221?
No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
How is CVE-2026-47221 attacked?
It is attacked over the network, in a hosted service.
Am I affected by CVE-2026-47221?
Check whether you run Envoy Proxy Envoy at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

A null pointer dereference exists in Envoy's router filter during the handling of HTTP 303 (See Other) internal redirects. When a body-less request (e.g., POST, PUT, DELETE, or PATCH with Content-Length: 0) is sent to a route configured with an internal redirect policy including 303, and the upstream server responds with a 303, Envoy attempts to drain a request body buffer that was never allocated. Specifically, `Filter::setupRedirect()` bypasses a null check, leading `convertRequestHeadersForInternalRedirect()` to call `modifyDecodingBuffer()` on a null `buffered_request_data_` pointer. This results in a segmentation fault (SIGSEGV) that crashes the Envoy process. The vulnerability is fixed in versions 1.35.13, 1.36.9, 1.37.5, and 1.38.3.

Affected products

  • Envoy Proxy Envoy 1.18.0 to 1.35.12, 1.36.0 to 1.36.8, 1.37.0 to 1.37.4, 1.38.0 to 1.38.2

Timeline

  • 2026-06-23: advisory: GitHub Security Advisory published by maintainers
  • 2026-06-26: disclosed: CVE-2026-47221 published to NVD

References

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