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Vulnerability record · CVE-2026-73552 · published 21 September 2026

CVE-2026-73552: Improper input validation vulnerability

Envoy is an open source edge and service proxy designed for cloud-native applications. Prior to 1.36.10, 1.37.6, 1.38.4, and 1.39.1, Envoy HTTP RBAC accepts RFC-valid opaque header bytes but evaluates safe_regex values with RE2's UTF-8 subject semantics. A downstream client can preserve a prohibited marker and add an unrelated obs-text octet, causing RE2::FullMatch to return false and a negative RBAC policy to treat the invalid subject as an ordinary no-match. A byte-oriented route matcher can still observe the marker, allowing the request to reach a route intended to be denied. The relevant scope boundary is that plain positive ALLOW regexes normally fail closed, and exact, prefix, suffix, and contains matchers are not shown to have this subject-domain failure. This issue is fixed in versions 1.36.10, 1.37.6, 1.38.4, and 1.39.1.

7.5 CVSS 3.1 High EPSS 0.66% · top 50.2% CWE-20 · Improper input validation Undergoing Analysis
7.5CVSS 3.1 base score
0.66%EPSS exploitation probability, 30 days
NoNot in CISA KEV
0Affected product versions listed by NVD
9References
23 Sep 2026Last modified by NVD

Description

Envoy is an open source edge and service proxy designed for cloud-native applications. Prior to 1.36.10, 1.37.6, 1.38.4, and 1.39.1, Envoy HTTP RBAC accepts RFC-valid opaque header bytes but evaluates safe_regex values with RE2's UTF-8 subject semantics. A downstream client can preserve a prohibited marker and add an unrelated obs-text octet, causing RE2::FullMatch to return false and a negative RBAC policy to treat the invalid subject as an ordinary no-match. A byte-oriented route matcher can still observe the marker, allowing the request to reach a route intended to be denied. The relevant scope boundary is that plain positive ALLOW regexes normally fail closed, and exact, prefix, suffix, and contains matchers are not shown to have this subject-domain failure. This issue is fixed in versions 1.36.10, 1.37.6, 1.38.4, and 1.39.1.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

References

LinkTags
https://github.com/envoyproxy/envoy/commit/5650cb9770d4420ec2bcbed8b90be06f564ecc07
https://github.com/envoyproxy/envoy/commit/7d1dee5dda66434d84437cc5c85153aa03955e26
https://github.com/envoyproxy/envoy/commit/c2b9a19dc081f03be6a9b4ca932673e5e7a33d18
https://github.com/envoyproxy/envoy/commit/f3726765f3a12ddc76dcb52c0b79bec3d95ced1c
https://github.com/envoyproxy/envoy/releases/tag/v1.36.10
https://github.com/envoyproxy/envoy/releases/tag/v1.37.6
https://github.com/envoyproxy/envoy/releases/tag/v1.38.4
https://github.com/envoyproxy/envoy/releases/tag/v1.39.1
https://github.com/envoyproxy/envoy/security/advisories/GHSA-23xh-2qxr-3xv8

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Source: NIST National Vulnerability Database (record CVE-2026-73552), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.