# CVE-2026-73550: Envoy HTTP/2 Host header denial of service

Source: https://junglewise.ai/threats/cve-2026-73550-envoy-is-an-open-source-edge-and-service-proxy-designed-for-cloud  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-21. Updated: 2026-09-26  
License: CC BY 4.0 with a link back

CVE-2026-73550 · Severity: high · CVSS 7.5 · Published 2026-09-21

Envoy is a cloud-native service proxy that routes traffic between applications. An unauthenticated attacker can exploit improper HTTP/2 header handling to force the proxy to allocate excessive memory and crash, causing service outages. The attack uses duplicate Host headers with HPACK compression to bypass header size limits.

Technologies: [Envoy](https://junglewise.ai/threats/technologies/envoy-envoy). Vendors: [Envoy](https://junglewise.ai/threats/vendors/envoy).

## Quick answers

**Is CVE-2026-73550 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-73550 being exploited in the wild.

**How severe is CVE-2026-73550?** High severity, with a CVSS score of 7.5, published 21 September 2026.

**Which products and versions are affected?** Envoy Prior to 1.36.10, 1.37.0 through 1.37.5, 1.38.0 through 1.38.3, 1.39.0.

**Is there a fix for CVE-2026-73550?** 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-2026-73550 attacked?** It is attacked over the network, in a hosted service.

**Am I affected by CVE-2026-73550?** Check whether you run 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

The vulnerability is a denial-of-service in HTTP/2 header processing where dropped Host headers (when :authority is present) are not charged against request header limits. An attacker can use HPACK indexing to reference a large Host header value repeatedly across multiple streams, causing unbounded memory allocation that leads to out-of-memory conditions. The fix requires versions 1.36.10, 1.37.6, 1.38.4, or 1.39.1 which properly account for dropped header sizes in limit checks.

## Affected products

- Envoy Envoy Prior to 1.36.10, 1.37.0 through 1.37.5, 1.38.0 through 1.38.3, 1.39.0

## Timeline

- 2026-09-21: disclosed

## References

- [https://github.com/envoyproxy/envoy/commit/0910997f70e91d2d20c329bb507bfce44ce01f80](https://github.com/envoyproxy/envoy/commit/0910997f70e91d2d20c329bb507bfce44ce01f80)
- [https://github.com/envoyproxy/envoy/commit/1fec994c868df008cdd4ae285aab58a196fd31f2](https://github.com/envoyproxy/envoy/commit/1fec994c868df008cdd4ae285aab58a196fd31f2)

## Related threats

- [Envoy authorization bypass via path parameter inconsistency](https://junglewise.ai/threats/cve-2026-73553-envoy-is-an-open-source-edge-and-service-proxy-designed-for-cloud)
- [Envoy path normalization bypass with semicolon parameters](https://junglewise.ai/threats/cve-2026-73551-envoy-is-an-open-source-edge-and-service-proxy-designed-for-cloud)
- [Envoy HTTP RBAC bypass via unsafe regex in headers](https://junglewise.ai/threats/cve-2026-73552-envoy-is-an-open-source-edge-and-service-proxy-designed-for-cloud)
- [Envoy scoped IPv6 address parsing denial of service](https://junglewise.ai/threats/cve-2026-73549-envoy-is-an-open-source-edge-and-service-proxy-designed-for-cloud)
- [Envoy null pointer dereference in ext_authz filter](https://junglewise.ai/threats/cve-2026-73547-envoy-is-an-open-source-edge-and-service-proxy-designed-for-cloud)