gRPC-Go: xDS RBAC HTTP Filter bypass via mixed-case Header Matching and gRFC A41 validation evasion

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

6.3 · 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 · score source

EPSS

• CVE-2026-84303: 0.31% estimated exploitation activity in the next 30 days; percentile 24.03 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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…

Published by the source

8 Sep 2026, 20:50 UTC

Last modified by the source

15 Sep 2026, 19:00 UTC

Source last checked

26 Oct 2026, 15:29 UTC

1. Revision 4 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-qc2q-p7wx-3px3

2. Revision 3 · amended · 25 Oct 2026

   Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

3. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GO-2026-6441

4. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-qc2q-p7wx-3px3

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# Patch Next advisory brief: CVE-2026-84303

Advisory: gRPC-Go: xDS RBAC HTTP Filter bypass via mixed-case Header Matching and gRFC A41 validation evasion
IDs: CVE-2026-84303, GHSA-qc2q-p7wx-3px3
Record: https://patchnext.com/advisories/cve-2026-84303 (revision 4, source checked 26 Oct 2026, 15:29 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: google.golang.org/grpc 1.83.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go google.golang.org/grpc: affected <= 1.83.0; fixed in 1.83.1

## Suggested inspection (read-only)
- Go google.golang.org/grpc: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on google.golang.org/grpc.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-qc2q-p7wx-3px3 (OSV record GHSA-qc2q-p7wx-3px3 lists affected ranges: Go google.golang.org/grpc >=0 <1.83.1 (fixed))
- Verified: https://osv.dev/vulnerability/GO-2026-6441 (OSV record GO-2026-6441 lists affected ranges: Go google.golang.org/grpc >=0 <1.83.1 (fixed))
- Verified: https://github.com/advisories/GHSA-qc2q-p7wx-3px3 (GitHub-reviewed advisory GHSA-qc2q-p7wx-3px3 lists affected ranges: Go google.golang.org/grpc >=0 <=1.83.0)

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