# Envoy Proxy QPACK decoding denial-of-service in HTTP/3

Source: https://junglewise.ai/threats/envoy-proxy-qpack-decoding-denial-of-service-in-http-3-95f03635  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-06-29. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

Severity: info · Published 2026-06-29

Envoy Proxy, a widely-used networking intermediary component for managing HTTP/3 connections, contains a flaw in QPACK header decompression that allows attackers to crash services handling HTTP/3 traffic. An attacker can send malformed requests that cause the HTTP/3 stack to stop responding, resulting in service unavailability for legitimate users.

Technologies: [Envoy Proxy](https://junglewise.ai/threats/technologies/envoy-proxy), [Google Cloud Platform](https://junglewise.ai/threats/technologies/google-cloud-platform). Vendors: [Envoy](https://junglewise.ai/threats/vendors/envoy), [Google](https://junglewise.ai/threats/vendors/google).

## Quick answers

**Is This vulnerability exploited in the wild?** No. Junglewise Threat Intelligence has no report of This vulnerability being exploited in the wild.

**How severe is This vulnerability?** Informational severity, published 29 June 2026.

**Which products and versions are affected?** Envoy Proxy <unknown>.

**Is there a fix for This vulnerability?** 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 This vulnerability attacked?** It is attacked over the network, in a software library.

**Am I affected?** Check whether you run Envoy Proxy or Google Cloud Platform 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 vulnerability in Envoy Proxy's QPACK (QUIC Package Compression) decoder allows a network-based attacker to cause a denial-of-service condition in the HTTP/3 stack. The flaw occurs when the decoder encounters blocked QPACK streams, which can be triggered by specially crafted HTTP/3 requests. The vulnerability is reachable over the network from any client capable of sending HTTP/3 traffic to an affected Envoy instance; no authentication is required. Successful exploitation causes the HTTP/3 connection handler to fail, rendering the proxy unable to process legitimate traffic. Patches are available through Google Cloud Service Mesh updates.

## Affected products

- Envoy Envoy Proxy <unknown>

## Timeline

- 2026-06-29: disclosed

## References

- [https://docs.cloud.google.com/support/bulletins/index](https://docs.cloud.google.com/support/bulletins/index)

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