CVE-2026-73552
Description
A flaw was found in Envoy. When evaluating regular expressions in role-based access control (RBAC) policies, Envoy improperly treats non-UTF-8 characters in HTTP header values as non-matching input. A remote attacker can exploit this flaw by sending requests with specially crafted HTTP headers to bypass negative matching rules, potentially gaining unauthorized access to protected resources.
Statement
This vulnerability is rated as an Important severity impact because unauthenticated remote attackers can bypass role-based access control (RBAC) restrictions enforced at the proxy layer to access unauthorized backend services. Within environments such as OpenShift Service Mesh, this flaw is triggered when RBAC policies employ inverted or negative matching rules against HTTP headers. If an incoming request includes arbitrary non-UTF-8 characters, Envoy fails to evaluate the pattern properly and inadvertently allows access to restricted resources instead of denying it. Deployments that rely on positive allowlists or exact header matching are unaffected by this authorization bypass.
Mitigation
Modify Envoy RBAC configurations or OpenShift Service Mesh authorization policies to avoid negative matching logic that relies on regular expressions for HTTP headers. Instead, configure policies using positive allowlists or employ non-regex matchers, such as exact, prefix, suffix, or contains matching rules, which evaluate header values reliably.
Caveats: Altering existing access control policies can modify request authorization decisions. Thoroughly test modified policy definitions in a staging environment prior to applying them in production.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 7.5 | N/A | 7.5 |
| Attack Vector | Network | N/A | Network |
| Attack Complexity | Low | N/A | Low |
| Privileges Required | None | N/A | None |
| User Interaction | None | N/A | None |
| Scope | Unchanged | N/A | Unchanged |
| Confidentiality | High | N/A | High |
| Integrity Impact | None | N/A | None |
| Availability Impact | None | N/A | None |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
cve.org: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Red Hat CVSS v3 Score Explanation
Adopting upstream CVSS for coordinated disclosure
Understanding the Weakness (CWE)
Confidentiality
Technical Impact: Read Application Data; Read Files or Directories
An attacker could bypass intended access restrictions to read sensitive data, either by reading the data directly from a data store that is not correctly restricted, or by accessing insufficiently-protected, privileged functionality to read the data.
Integrity
Technical Impact: Modify Application Data; Modify Files or Directories
An attacker could bypass intended access restrictions to modify sensitive data, either by writing the data directly to a data store that is not correctly restricted, or by accessing insufficiently-protected, privileged functionality to write the data.
Access Control
Technical Impact: Gain Privileges or Assume Identity; Bypass Protection Mechanism
An attacker could bypass intended access restrictions to gain privileges by modifying or reading critical data directly, or by accessing privileged functionality.
Confidentiality,Integrity,Availability
Technical Impact: Execute Unauthorized Code or Commands
An attacker could use elevated privileges to execute unauthorized commands or code.
Availability
Technical Impact: DoS: Crash, Exit, or Restart; DoS: Resource Consumption (CPU); DoS: Resource Consumption (Memory); DoS: Resource Consumption (Other)
An attacker could gain unauthorized access to resources on the system and excessively consume those resources, leading to a denial of service.
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