CVE-2026-73552: CWE-20: Improper Input Validation in envoyproxy envoy
Envoy proxy versions prior to 1.36.10, 1.37.6, 1.38.4, and 1.39.1 contain an improper input validation vulnerability in the HTTP RBAC component. This flaw allows a downstream client to bypass negative RBAC policies by exploiting differences in how opaque header bytes are evaluated with RE2's UTF-8 semantics, potentially permitting unauthorized requests to reach routes intended to be denied. The issue is fixed in the specified patched versions.
AI Analysis
Technical Summary
Envoy proxy's HTTP RBAC prior to versions 1.36.10, 1.37.6, 1.38.4, and 1.39.1 improperly validates input due to a mismatch between accepting RFC-valid opaque header bytes and evaluating safe_regex values using RE2's UTF-8 subject semantics. A crafted request can preserve a prohibited marker and add an unrelated obs-text octet, causing RE2::FullMatch to return false. This leads a negative RBAC policy to treat the invalid subject as a no-match, allowing the request to bypass intended route denial. Positive ALLOW regexes and other matcher types are not affected by this subject-domain failure. The vulnerability is addressed in the listed fixed versions.
Potential Impact
An attacker can bypass negative RBAC policies in Envoy proxy, potentially allowing unauthorized access to routes that should be denied. The vulnerability does not affect confidentiality or availability but impacts access control integrity. There are no known exploits in the wild at this time.
Mitigation Recommendations
Upgrade Envoy proxy to versions 1.36.10, 1.37.6, 1.38.4, or 1.39.1 or later, where this issue is fixed. No other mitigations are indicated by the vendor advisory.
CVE-2026-73552: CWE-20: Improper Input Validation in envoyproxy envoy
Description
Envoy proxy versions prior to 1.36.10, 1.37.6, 1.38.4, and 1.39.1 contain an improper input validation vulnerability in the HTTP RBAC component. This flaw allows a downstream client to bypass negative RBAC policies by exploiting differences in how opaque header bytes are evaluated with RE2's UTF-8 semantics, potentially permitting unauthorized requests to reach routes intended to be denied. The issue is fixed in the specified patched versions.
CVSS v3.1
Score 7.5high
Affected software
envoyproxy
envoy
pkg:github/envoyproxy/envoyRun on your own infrastructure? Check whether these packages are installed with threat-finder — our free open-source scanner.
Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
Envoy proxy's HTTP RBAC prior to versions 1.36.10, 1.37.6, 1.38.4, and 1.39.1 improperly validates input due to a mismatch between accepting RFC-valid opaque header bytes and evaluating safe_regex values using RE2's UTF-8 subject semantics. A crafted request can preserve a prohibited marker and add an unrelated obs-text octet, causing RE2::FullMatch to return false. This leads a negative RBAC policy to treat the invalid subject as a no-match, allowing the request to bypass intended route denial. Positive ALLOW regexes and other matcher types are not affected by this subject-domain failure. The vulnerability is addressed in the listed fixed versions.
Potential Impact
An attacker can bypass negative RBAC policies in Envoy proxy, potentially allowing unauthorized access to routes that should be denied. The vulnerability does not affect confidentiality or availability but impacts access control integrity. There are no known exploits in the wild at this time.
Mitigation Recommendations
Upgrade Envoy proxy to versions 1.36.10, 1.37.6, 1.38.4, or 1.39.1 or later, where this issue is fixed. No other mitigations are indicated by the vendor advisory.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-08-12T20:53:46.380Z
- Cvss Version
- 3.1
- State
- PUBLISHED
Threat ID: 6ab189c655bf5e2cf56100f1
Added to database: 09/21/2026, 19:47:18 UTC
Last enriched: 09/21/2026, 20:01:29 UTC
Last updated: 09/21/2026, 20:01:30 UTC
Views: 5
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