# CVE-2026-73552: Envoy HTTP RBAC bypass via unsafe regex in headers

Source: https://junglewise.ai/threats/cve-2026-73552-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-2026-73552 · Severity: high · CVSS 7.5 · Published 2026-09-21

Envoy is a widely-used network proxy that enforces access control policies on HTTP traffic. The vulnerability allows a malicious downstream client to bypass HTTP role-based access control (RBAC) policies by crafting specially-formed header bytes that exploit a regex evaluation flaw. An attacker can reach routes that should be denied by the RBAC policy, potentially leading to unauthorized access to protected services.

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

## Quick answers

**Is CVE-2026-73552 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-73552 being exploited in the wild.

**How severe is CVE-2026-73552?** High severity, with a CVSS score of 7.5, published 21 September 2026.

**Which products and versions are affected?** Envoy before 1.36.10, 1.37.0-1.37.5, 1.38.0-1.38.3, 1.39.0.

**Is there a fix for CVE-2026-73552?** A patch was published on 2026-08-26: Fix committed in versions 1.36.10, 1.37.6, 1.38.4, and 1.39.1 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-73552 attacked?** It is attacked over the network, in a hosted service.

**Am I affected by CVE-2026-73552?** 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 HTTP RBAC implementation, which evaluates safe_regex policy expressions using RE2's UTF-8 subject semantics even though HTTP headers are Latin1-encoded bytes. An attacker can preserve a prohibited marker in the header and append an invalid obs-text octet, causing RE2::FullMatch to return false for negative RBAC policies while a byte-oriented route matcher still observes the marker. The fix switches safe_regex charset mode from UTF-8 to Latin1 to properly handle HTTP header bytes.

## Affected products

- Envoy Envoy before 1.36.10, 1.37.0-1.37.5, 1.38.0-1.38.3, 1.39.0

## Timeline

- 2026-09-21: disclosed
- 2026-08-26: patched: Fix committed in versions 1.36.10, 1.37.6, 1.38.4, and 1.39.1

## References

- [https://github.com/envoyproxy/envoy/commit/5650cb9770d4420ec2bcbed8b90be06f564ecc07](https://github.com/envoyproxy/envoy/commit/5650cb9770d4420ec2bcbed8b90be06f564ecc07)
- [https://github.com/envoyproxy/envoy/commit/7d1dee5dda66434d84437cc5c85153aa03955e26](https://github.com/envoyproxy/envoy/commit/7d1dee5dda66434d84437cc5c85153aa03955e26)

## 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/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 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)