What’s Vulnerable › Vulnerabilities

CVE-2026-84303: gRPC-Go: xDS RBAC HTTP Filter bypass via mixed-case Header Matching and gRFC A41 validation evasion

• Severity: medium (CVSS 6.3 v4.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-09-01 · updated 2026-09-09
• Weakness: CWE-178

Description

gRPC-Go is the Go language implementation of gRPC. Prior to 1.83.1, the xDS RBAC HTTP filter in internal/xds/httpfilter/rbac/rbac.go does not lowercase header matcher names in normalizeHeaderMatcher even though incoming metadata keys are lowercase. A DENY policy using a mixed-case name such as X-Role or User-Agent therefore does not match and fails open, allowing requests that should be rejected. The same case mismatch permits :Scheme or Grpc-Status to evade gRFC A41 validation and prevents Host from being rewritten to :authority. This issue is fixed in version 1.83.1.

Affected products

• Google.Golang.Org/Grpc: before 1.83.1 — fixed in 1.83.1
• Google gRPC: before 1.83.1

How to fix

Upgrade to a fixed version: Google.Golang.Org/Grpc 1.83.1. Check the vendor advisory for mitigations.

References

• https://github.com/grpc/grpc-go/commit/db9482836c298f234c896cf82ab68cafc78237f8
• https://github.com/grpc/grpc-go/commit/ebba6f3f1b206e2b4dc4d1d5a96d18430302c2fe
• https://github.com/grpc/grpc-go/pull/9332
• https://github.com/grpc/grpc-go/pull/9335
• https://github.com/grpc/grpc-go/releases/tag/v1.83.1
• https://github.com/grpc/grpc-go/security/advisories/GHSA-qc2q-p7wx-3px3

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