CVE-2026-84303: gRPC-Go XDS RBAC HTTP Filter Bypass Vulnerability

MODERATE
Advisory Identifier: GHSA-qc2q-p7wx-3px3
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CWE-863 CWE-178
Published
Advisory Summary

CVE-2026-84303 is a MODERATE xds rbac http filter bypass vulnerability (CWE-863: Incorrect Authorization) affecting gRPC-Go libraries in the Go ecosystem. The issue involves xds rbac http filter bypass via mixed-case header matching and grfc a41 validation evasion. Remediation is available by upgrading affected packages to version 1.83.1.

CVE-2026-84303 at a Glance

CVE Identifier CVE-2026-84303
GHSA Identifier GHSA-qc2q-p7wx-3px3
Severity MODERATE
CVSS v3.1 Base Score N/A
CWE Classification CWE-863: Incorrect Authorization
Affected Product gRPC-Go
Package Ecosystem Go
Published Date
Last Updated

How to Fix CVE-2026-84303

To remediate this vulnerability, upgrade all affected gRPC-Go dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

google.golang.org/grpc fixed: 1.83.1 
Upgrade google.golang.org/grpc to 1.83.1
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

inspect dependencies for google.golang.org/grpc

How to Check if You Are Affected

To determine whether your application is affected by CVE-2026-84303, inspect your project dependencies for gRPC-Go:

inspect dependencies for google.golang.org/grpc

Analyze the terminal output to locate any version of gRPC-Go in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 1.83.1), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-863: Incorrect Authorization, where the product performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check. In gRPC-Go, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### 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.

CVE-2026-84303 Affected gRPC-Go Versions

1 component(s)
Fixed Versions:
1.83.1
Product / Package Ecosystem Affected Versions Fixed Version
google.golang.org/grpc
golang/google.golang.org/grpc
Go
< 1.83.1
1.83.1

References

GitHub Advisory / Wiki ADVISORY
https://github.com/grpc/grpc-go/security/advisories/GHSA-qc2q-p7wx-3px3
NVD — CVE-2026-84303 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-84303
gRPC-Go Source Repository REPOSITORY
https://github.com/grpc/grpc-go/pull/9332
gRPC-Go Source Repository REPOSITORY
https://github.com/grpc/grpc-go/pull/9335
Security Fix Commit FIX COMMIT
https://github.com/grpc/grpc-go/commit/db9482836c298f234c896cf82ab68cafc78237f8
Security Fix Commit FIX COMMIT
https://github.com/grpc/grpc-go/commit/ebba6f3f1b206e2b4dc4d1d5a96d18430302c2fe
gRPC-Go Source Repository REPOSITORY
https://github.com/grpc/grpc-go
gRPC-Go Release RELEASE
https://github.com/grpc/grpc-go/releases/tag/v1.83.1

Frequently Asked Questions

What is CVE-2026-84303?
CVE-2026-84303 is a security vulnerability in gRPC-Go involving xDS RBAC HTTP Filter bypass via mixed-case Header Matching and gRFC A41 validation evasion under CWE-863: Incorrect Authorization.
Which gRPC-Go versions are affected?
Affected versions include releases prior to 1.83.1 across affected packages: google.golang.org/grpc.
What version fixes CVE-2026-84303?
Upgrading to 1.83.1 (or the latest patched release for your respective branch) resolves the vulnerability.
Is google.golang.org/grpc affected?
Yes, google.golang.org/grpc is affected in releases prior to 1.83.1. Upgrade your dependency to 1.83.1 or later.
What CWE is associated with CVE-2026-84303?
CVE-2026-84303 is classified under CWE-863: Incorrect Authorization (The product performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check.).
How can I check Go dependencies for CVE-2026-84303?
Run the dependency tree command: 'inspect dependencies for google.golang.org/grpc'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-qc2q-p7wx-3px3",
  "modified" : "2026-09-08T20:50:21Z",
  "published" : "2026-09-08T20:50:21Z",
  "aliases" : [ "CVE-2026-84303" ],
  "summary" : "gRPC-Go: xDS RBAC HTTP Filter bypass via mixed-case Header Matching and gRFC A41 validation evasion",
  "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.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "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"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "google.golang.org/grpc"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "1.83.1"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 1.83.0"
    }
  } ],
  "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"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-178", "CWE-863" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-09-08T20:50:21Z",
    "nvd_published_at" : "2026-09-01T19:17:30Z"
  }
}