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9.1

gRPC-Go servers may skip access checks via malformed path

CVE-2026-33186 · published 6 months ago
Summary

If a gRPC-Go server receives a request whose path is missing the leading slash, the server can route the call but the built‑in access‑control checks may not apply, potentially allowing unwanted actions. This occurs in versions before the fix that added a check for the missing slash. Upgrade to the latest version of gRPC-Go (1.79.3 or later) or add a filter that rejects requests whose path does not start with '/'.

What to do
  • Update google.golang.org grpc to version 1.79.3.
  • Update grpc google.golang.org/grpc to version 1.79.3.
  • Update grpc rootio-google.golang.org/grpc to version v1.72.0-root.io.1.
  • Update grpc rootio-google.golang.org/grpc to version v1.78.0-root.io.1.
  • Update grpc rootio-google.golang.org/grpc to version v1.65.0-root.io.2.
  • Update grpc google.golang.org/grpc to version v1.65.0-aikido.2.
  • Update bellsoft docker to version 29.4.0-r0.
  • Update grpc google.golang.org/grpc to version v1.71.0-aikido.3.
  • Update grpc rootio-google.golang.org/grpc to version v1.71.0-root.io.3.
  • Update debian golang-google-grpc to version 1.79.3-1.
  • Update grpc google.golang.org/grpc to version v1.77.0-aikido.5.
  • Update grpc rootio-google.golang.org/grpc to version v1.77.0-root.io.5.
  • Update grpc google.golang.org/grpc to version v1.65.0-aikido.5.
  • Update grpc rootio-google.golang.org/grpc to version v1.65.0-root.io.5.
  • Update grpc google.golang.org/grpc to version v1.76.0-aikido.1.
  • Update grpc rootio-google.golang.org/grpc to version v1.76.0-root.io.1.
  • Update grpc grpc to version 1.79.3 or later.
Affected software
Ecosystem VendorProductAffected versions
go google.golang.org grpc < 1.79.3
Fix: upgrade to 1.79.3
Go grpc google.golang.org/grpc < 1.79.3
Fix: upgrade to 1.79.3
Ubuntu:22.04:LTS canonical golang-google-grpc All versions
Ubuntu:22.04:LTS canonical google-guest-agent All versions
Ubuntu:24.04:LTS canonical google-guest-agent All versions
Ubuntu:Pro:24.04:LTS canonical golang-google-grpc All versions
Ubuntu:25.10 canonical golang-google-grpc All versions
Ubuntu:25.10 canonical google-guest-agent All versions
Ubuntu:26.04:LTS canonical golang-google-grpc All versions
Ubuntu:26.04:LTS canonical google-guest-agent All versions
Debian:11 debian golang-google-grpc All versions
Debian:12 debian golang-google-grpc All versions
Debian:13 debian golang-google-grpc All versions
Debian:14 debian golang-google-grpc < 1.79.3-1
Fix: upgrade to 1.79.3-1
– grpc grpc < 1.79.3
cpe:2.3:a:grpc:grpc:*:*:*:*:*:go:*:*
Root:Go grpc rootio-google.golang.org/grpc < v1.72.0-root.io.1
< v1.78.0-root.io.1
< v1.65.0-root.io.2
< v1.71.0-root.io.3
< v1.77.0-root.io.5
< v1.65.0-root.io.5
< v1.76.0-root.io.1
Fix: upgrade to v1.72.0-root.io.1
Root:Go grpc google.golang.org/grpc < v1.65.0-aikido.2
< v1.71.0-aikido.3
< v1.77.0-aikido.5
< v1.65.0-aikido.5
< v1.76.0-aikido.1
Fix: upgrade to v1.65.0-aikido.2
Ubuntu:16.04:LTS canonical golang-google-grpc All versions
Ubuntu:Pro:16.04:LTS canonical google-guest-agent All versions
Ubuntu:18.04:LTS canonical golang-google-grpc All versions
Ubuntu:Pro:18.04:LTS canonical google-guest-agent All versions
Ubuntu:Pro:20.04:LTS canonical google-guest-agent All versions
Ubuntu:20.04:LTS canonical golang-google-grpc All versions
– grpc grpc-go < 1.79.3
Alpaquita:stream bellsoft docker >= 24.0.2-r0, < 29.4.0-r0
Fix: upgrade to 29.4.0-r0
Original advisory text
gRPC-Go has an authorization bypass via missing leading slash in :path
gRPC-Go is the Go language implementation of gRPC. Versions prior to 1.79.3 have an authorization bypass resulting from improper input validation of the HTTP/2 `:path` pseudo-header. The gRPC-Go server was too lenient in its routing logic, accepting requests where the `:path` omitted the mandatory leading slash (e.g., `Service/Method` instead of `/Service/Method`). While the server successfully routed these requests to the correct handler, authorization interceptors (including the official `grpc/authz` package) evaluated the raw, non-canonical path string. Consequently, "deny" rules defined using canonical paths (starting with `/`) failed to match the incoming request, allowing it to bypass the policy if a fallback "allow" rule was present. This affects gRPC-Go servers that use path-based authorization interceptors, such as the official RBAC implementation in `google.golang.org/grpc/authz` or custom interceptors relying on `info.FullMethod` or `grpc.Method(ctx)`; AND that have a security policy contains specific "deny" rules for canonical paths but allows other requests by default (a fallback "allow" rule). The vulnerability is exploitable by an attacker who can send raw HTTP/2 frames with malformed `:path` headers directly to the gRPC server. The fix in version 1.79.3 ensures that any request with a `:path` that does not start with a leading slash is immediately rejected with a `codes.Unimplemented` error, preventing it from reaching authorization interceptors or handlers with a non-canonical path string. While upgrading is the most secure and recommended path, users can mitigate the vulnerability using one of the following methods: Use a validating interceptor (recommended mitigation); infrastructure-level normalization; and/or policy hardening.
References
Fix within
Internet-facing 14 days
Internal 60 days
  • Not known to be exploited
  • Can be exploited automatically
  • Gives an attacker partial control
Severity
9.1 Critical
Exploitation
2% chance of attack within 30 days
Type
CWE-285Improper Authorization
CWE-551Incorrect Behavior Order: Authorization Before Parsing and Canonicalization
Timeline
Published20 Mar 2026
Updated12 Oct 2026
First seen18 Mar 2026
Sources
DEBIAN-CVE-2026-33186 · OSV
ROOT-APP-GOBINARY-CVE-2026-33186 · OSV
UBUNTU-CVE-2026-33186 · OSV
GHSA-p77j-4mvh-x3m3 · GHSA
CVE-2026-33186 · NVD
GO-2026-4762 · OSV
CVE-2026-33186 · OSV
CVE-2026-33186 · MITRE
BELL-CVE-2026-33186 · OSV
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