CVE-2026-126367 in grpc-node
Summary
by MITRE • 11/13/2026
@grpc/grpc-js implements the core functionality of gRPC purely in JavaScript, without a C++ addon. Before 1.13.2, and from 1.14.0 through 1.14.1, the @grpc/grpc-js-xds SafeRegexValueMatcher and PathSafeRegexValueMatcher add start and end anchors without grouping a supplied top-level alternation. An expression intended to match one of several complete values can therefore match a prefix, substring, or suffix. The affected matchers are used for route selection, xDS credential identity matching, and RBAC URL path, principal name, server name, and header rules. An ALLOW policy using an alternation can consequently accept a method, certificate identity, or header value outside the intended set, while a DENY policy becomes broader rather than permissive. This issue is fixed in versions 1.13.2 and 1.14.2.
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Analysis
by VulDB Data Team • 11/13/2026
The vulnerability identified in @grpc/grpc-js stems from an incorrect implementation of regular expression anchoring within the xDS configuration processing logic, specifically affecting SafeRegexValueMatcher and PathSafeRegexValueMatcher components prior to version 1.13.2 and between versions 1.14.0 through 1.14.1. In these affected releases, when a top-level alternation pattern was supplied by an administrator or service mesh controller, the library automatically prepended start anchors and appended end anchors without properly grouping the entire alternation expression within parentheses. This technical flaw fundamentally alters the scope of the regular expression match operation because standard regex engines interpret ungrouped alternations with external anchors as applying those anchors to each individual alternative branch independently rather than to the collective set. Consequently, an expression designed to match one of several complete distinct values can inadvertently match a prefix, substring, or suffix of unintended inputs, thereby bypassing intended logical constraints and expanding the matching surface area beyond what was explicitly configured by security policies.
This flaw has significant operational implications for service mesh environments relying on gRPC for control plane communication via xDS protocols such as Cluster Discovery Service (CDS), Listener Discovery Service (LDS), Route Discovery Service (RDS), and Secret Discovery Service (SDS). The affected matchers are critical components in route selection, credential identity verification, and Role-Based Access Control RBAC enforcement. Specifically, they govern URL path matching, principal name validation for mutual TLS authentication, server name indication checks, and header value filtering. When an ALLOW policy utilizes a regular expression with alternations to permit specific methods or identities, the lack of proper grouping allows requests containing substrings that partially match one of the allowed alternatives to be accepted even if they do not fully conform to any single intended option. This results in unauthorized access where clients presenting malformed but substring-matching credentials are granted permissions reserved for legitimate entities.
Conversely, when a DENY policy employs similar regex patterns with alternations, the anchoring error causes the rule to become broader rather than more restrictive as might be intuitively expected from loose matching behavior. This means that traffic which should have been explicitly blocked because it matched one of several malicious or unauthorized signatures may slip through if it only partially matches a branch due to substring inclusion without full boundary adherence. In RBAC contexts, this can lead to privilege escalation where users with restricted access levels are able to invoke API endpoints they should not reach simply by providing header values or path segments that contain substrings matching denied patterns in unintended ways. The cumulative effect is a degradation of the security posture provided by service mesh policies, allowing both unauthorized ingress and insufficient egress filtering depending on policy configuration.
The vulnerability aligns with CWE-78 Improper Neutralization of Special Elements used in an OS Command known as Regular Expression Injection when applied to input validation contexts, specifically reflecting issues related to incomplete anchoring or grouping that lead to unintended pattern matching behavior similar to CWE-1325 Incorrect Regular Expression Syntax which results in a security bypass. In terms of the MITRE ATT&CK framework, this flaw facilitates Initial Access and Privilege Escalation techniques by allowing attackers to craft gRPC requests with carefully constructed headers, paths, or certificate identities that evade detection mechanisms relying on these flawed regex matchers. Attackers can exploit this to perform unauthorized data exfiltration or disrupt service availability by bypassing rate limiting or authentication checks embedded within the xDS configuration rules.
To mitigate this risk, organizations must upgrade @grpc/grpc-js to version 1.13.2 or later, with particular emphasis on upgrading past version 1.14.1 if using newer releases where the bug persists until patch level 1.14.2. For environments unable to immediately update dependencies, manual review of all xDS configuration files containing regular expressions used in RBAC rules, route matching, and credential validation is required. Administrators should ensure that any alternation patterns are explicitly wrapped in non-capturing groups using the syntax (?:...) before being passed to the matcher functions if custom code paths bypass standard library abstractions. Additionally, implementing strict input validation at the application layer for gRPC metadata headers can provide a secondary defense-in-depth measure against substring-based evasion attempts until the underlying library vulnerability is fully remediated across all service instances.