{"id":"CVE-2026-84303","aliases":["GHSA-qc2q-p7wx-3px3","GO-2026-6441"],"url":"https://o3.security/vulnerability/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.","published":"2026-09-01T18:14:37.870Z","modified":"2026-10-21T03:00:28.773360198Z","cvss":null,"epss":{"score":0.00311,"percentile":0.23892,"asOf":"2026-09-16"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"Go","name":"google.golang.org/grpc","fixedVersion":"1.83.1"}],"fix":{"url":"https://github.com/grpc/grpc-go/commit/db9482836c298f234c896cf82ab68cafc78237f8","label":"grpc/grpc-go@db94828"},"references":[{"type":"WEB","url":"https://github.com/grpc/grpc-go/releases/tag/v1.83.1"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/84xxx/CVE-2026-84303.json"},{"type":"ADVISORY","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":"FIX","url":"https://github.com/grpc/grpc-go/commit/db9482836c298f234c896cf82ab68cafc78237f8"},{"type":"FIX","url":"https://github.com/grpc/grpc-go/commit/ebba6f3f1b206e2b4dc4d1d5a96d18430302c2fe"},{"type":"FIX","url":"https://github.com/grpc/grpc-go/pull/9332"},{"type":"FIX","url":"https://github.com/grpc/grpc-go/pull/9335"},{"type":"PACKAGE","url":"https://github.com/grpc/grpc-go"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-21T03:00:28.773360198Z"}}