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GHSA-QC2Q-P7WX-3PX3

Vulnerability from github – Published: 2026-09-08 20:50 – Updated: 2026-09-08 20:50
VLAI
Summary
gRPC-Go: xDS RBAC HTTP Filter bypass via mixed-case Header Matching and gRFC A41 validation evasion
Details

Summary

A vulnerability in the xDS RBAC HTTP filter implementation in grpc-go allows remote attackers to bypass authorization policies (specifically DENY rules) by using mixed-case or canonical-case header matchers (e.g., X-Role instead of x-role). Additionally, the safety guards introduced by gRFC A41 to block grpc- prefixed headers can be evaded via variations in casing (e.g., Grpc-Status).

Impact

When an operator defines an RBAC policy referencing headers containing uppercase letters (e.g. X-Role), grpc-go fails to match incoming metadata keys because they are unconditionally lowercased. Because of this case-sensitivity mismatch, a policy designed to block requests containing specific header values fails open: the rule is evaluated as a non-match, and traffic that should have been rejected is served.

Furthermore, gRFC A41 requires rejecting configuration schemas specifying header matchers starting with grpc-. Because this check is executed case-sensitively in grpc-go, attackers can bypass the validation by specifying titles like Grpc-Status.

Patches

The problem is fixed in master and in the 1.83.1 release.

Severity
6.3 (Medium)
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N
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{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 1.83.0"
      },
      "package": {
        "ecosystem": "Go",
        "name": "google.golang.org/grpc"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "1.83.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-84303"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-178",
      "CWE-863"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-09-08T20:50:21Z",
    "nvd_published_at": "2026-09-01T19:17:30Z",
    "severity": "MODERATE"
  },
  "details": "### Summary\nA vulnerability in the xDS RBAC HTTP filter implementation in grpc-go allows remote attackers to bypass authorization policies (specifically DENY rules) by using mixed-case or canonical-case header matchers (e.g., X-Role instead of x-role). Additionally, the safety guards introduced by gRFC A41 to block grpc- prefixed headers can be evaded via variations in casing (e.g., Grpc-Status).\n\n### Impact\nWhen an operator defines an RBAC policy referencing headers containing uppercase letters (e.g. X-Role), grpc-go fails to match incoming metadata keys because they are unconditionally lowercased. Because of this case-sensitivity mismatch, a policy designed to block requests containing specific header values fails open: the rule is evaluated as a non-match, and traffic that should have been rejected is served.\n\nFurthermore, gRFC A41 requires rejecting configuration schemas specifying header matchers starting with grpc-. Because this check is executed case-sensitively in grpc-go, attackers can bypass the validation by specifying titles like Grpc-Status.\n\n### Patches\nThe problem is fixed in `master` and in the 1.83.1 release.",
  "id": "GHSA-qc2q-p7wx-3px3",
  "modified": "2026-09-08T20:50:21Z",
  "published": "2026-09-08T20:50:21Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/grpc/grpc-go/security/advisories/GHSA-qc2q-p7wx-3px3"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-84303"
    },
    {
      "type": "WEB",
      "url": "https://github.com/grpc/grpc-go/pull/9332"
    },
    {
      "type": "WEB",
      "url": "https://github.com/grpc/grpc-go/pull/9335"
    },
    {
      "type": "WEB",
      "url": "https://github.com/grpc/grpc-go/commit/db9482836c298f234c896cf82ab68cafc78237f8"
    },
    {
      "type": "WEB",
      "url": "https://github.com/grpc/grpc-go/commit/ebba6f3f1b206e2b4dc4d1d5a96d18430302c2fe"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/grpc/grpc-go"
    },
    {
      "type": "WEB",
      "url": "https://github.com/grpc/grpc-go/releases/tag/v1.83.1"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "gRPC-Go: xDS RBAC HTTP Filter bypass via mixed-case Header Matching and gRFC A41 validation evasion"
}



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