CVE-2026-33186: grpc-go · Improper Authorization
Affects grpc-goSource CVE Database V5
Not known to be exploited · CVSS 9.1 Critical : upgrade to 1.79.3 as a priority.
Data as of 2 Nov 2026, 10:58 UTC
- EPSS
- 1.5% chance of exploitation in 30 days – higher than 75% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
- Patch
- Available – fixed in 1.79.3
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:NExploitation evidence
Disclosed: evidence found.
CVE published 20 Mar 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: evidence found.
Public exploit code: GitHub proofs of concept
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), GitHub proofs of concept, the Metasploit, Exploit-DB and nuclei-templates index as of 2 Nov 2026.
What to do
Upgrade grpc-go and github.com/grpc/grpc-go to 1.79.3.
Affected software
| Product | Affected | Fixed in |
|---|---|---|
| grpcgrpc-go | Affected
| Fixed in
|
Gogithub.com/grpc/grpc-gopkg:golang/github.com/grpc/grpc-goOther threats | Affected
| Fixed in
|
Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.
AI-suggested
A fix is available in grpc-go version 1.79.3. Users should upgrade to this version to resolve the vulnerability. Alternatively, infrastructure-level mitigation can be applied by configuring a reverse proxy or API gateway to normalize incoming HTTP/2 :path headers, ensuring they include the mandatory leading slash before reaching the grpc-go server. Proper configuration and restarting of intermediaries is required to apply this mitigation. No other vendor official fixes or workarounds are indicated.
Description
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
- github.com/grpc/grpc-go/security/advisories/GHSA-p77j-4mvh-x3m3 (opens in a new tab)
- access.redhat.com/security/cve/CVE-2026-33186 (opens in a new tab)
- bugzilla.redhat.com/show_bug.cgi?id=2449833 (opens in a new tab)
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