# CVE-2026-73549: Envoy scoped IPv6 address parsing denial of service

Source: https://junglewise.ai/threats/cve-2026-73549-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-2026-73549 · Severity: medium · CVSS 5.3 · Published 2026-09-21

Envoy is a cloud-native proxy that routes network traffic for applications. In deployments using transparent proxying or QUIC connections with IPv6 scoped addresses, a malformed IPv6 address containing a scope identifier can crash the Envoy process, causing a service outage. This affects versions prior to 1.36.10, 1.37.6, 1.38.4, and 1.39.1.

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

## Quick answers

**Is CVE-2026-73549 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-73549 being exploited in the wild.

**How severe is CVE-2026-73549?** Medium severity, with a CVSS score of 5.3, published 21 September 2026.

**Which products and versions are affected?** Envoy before 1.36.10, 1.37.x before 1.37.6, 1.38.x before 1.38.4, 1.39.x before 1.39.1.

**Is there a fix for CVE-2026-73549?** A patch was published on 2026-09-21: Versions 1.36.10, 1.37.6, 1.38.4, and 1.39.1 include the fix Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-73549 attacked?** It is attacked over the network, in a hosted service.

**Am I affected by CVE-2026-73549?** 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 exists in Envoy's Utility::copyInternetAddressAndPort and QUIC client-address parsing code, which reconstructs scoped IPv6 addresses as strings including percent-encoded scope identifiers. When these strings are parsed with inet_pton, the parser cannot handle the scope identifier, triggering an exception or process abort. Exploitation requires either a kernel-provided original destination in transparent-proxy deployments or a malformed address via the QUIC connection path; HTTP requests using the use_http_header override filter out scoped addresses earlier and are not affected.

## Affected products

- Envoy Envoy before 1.36.10, 1.37.x before 1.37.6, 1.38.x before 1.38.4, 1.39.x before 1.39.1

## Timeline

- 2026-09-21: disclosed
- 2026-09-21: patched: Versions 1.36.10, 1.37.6, 1.38.4, and 1.39.1 include the fix

## References

- [https://github.com/envoyproxy/envoy/commit/109e5a5b08ad10d99074cefd55a747a16ee64da7](https://github.com/envoyproxy/envoy/commit/109e5a5b08ad10d99074cefd55a747a16ee64da7)
- [https://github.com/envoyproxy/envoy/commit/59b1744a6cb62746db418ac06fc5e359fd25fdb7](https://github.com/envoyproxy/envoy/commit/59b1744a6cb62746db418ac06fc5e359fd25fdb7)

## 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 HTTP/2 Host header denial of service](https://junglewise.ai/threats/cve-2026-73550-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)