Bug 2526949 (CVE-2026-84303)

Summary: CVE-2026-84303 github.com/grpc/grpc-go: gRPC-Go: RBAC policy bypass and validation evasion via mixed-case header matching
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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Priority: medium    
Version: unspecifiedKeywords: Security
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OS: Linux   
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A flaw was found in gRPC-Go, the Go language implementation of gRPC. The xDS RBAC HTTP filter does not correctly process header matcher names when they use mixed-case. This allows a remote attacker to bypass configured DENY policies by sending requests with mixed-case header names, leading to unauthorized access. Additionally, this case mismatch can enable evasion of gRFC A41 validation and prevent the Host header from being properly rewritten.
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Description OSIDB Bzimport 2026-09-01 18:27:31 UTC 
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.