CVE-2026-33186 | 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.

Published: 2026-03-20 Last update: 2026-04-10 Assigner: [email protected] Source: [email protected]
NVD Status：Analyzed，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2026-33186 is rated Low Risk (37.1/100): CVSS Critical severity, with low exploitation likelihood (EPSS 0.01%). Monitor for updates and reassess as exploit intelligence or EPSS changes.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2026-33186

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-03-21 — 0.01% —

Full EPSS history (1 record total)

Common vulnerability scoring system (CVSS) metrics for CVE-2026-33186

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
9.1 3.1 CRITICAL
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:N)
Service keeps running; no real outage angle.
 3.9 5.2 [email protected]

Weakness enumeration for CVE-2026-33186

GitHub Security Advisory for CVE-2026-33186

GHSA-p77j-4mvh-x3m3 · Severity: critical · Ecosystem: go — gRPC-Go has an authorization bypass via missing leading slash in :path

OS Trackers for CVE-2026-33186

vendor priority summary link
alpine — CVE-2026-33186: 1 source package rows (grpc); 19 state rows across 2 repos (3.23-community, edge-community); fixed 0, open 19. https://security.alpinelinux.org/vuln/CVE-2026-33186
debian not yet assigned CVE-2026-33186 not yet assigned priority: Debian including 1 source packages (golang-google-grpc), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): open 3, resolved 2. https://security-tracker.debian.org/tracker/CVE-2026-33186
redhat high — https://access.redhat.com/security/cve/CVE-2026-33186
suse high CVE-2026-33186 severity important: SUSE including 367 source package names (amazon-cloudwatch-agent-1.300064.0-2.1, amazon/suse-sles-15-sp1-chost-byos-v20210304-hvm-ssd-x86_64, …), 662 product×package rows across 38 product lines (Image SLES12-SP5-GCE-SAP-BYOS, Image SLES12-SP5-GCE-SAP-On-Demand, … (38 product lines)): Known Not Affected 296, Known Affected 231, Fixed 66, Will Not Fix 53, First Fixed 16. https://www.suse.com/security/cve/CVE-2026-33186/
ubuntu high CVE-2026-33186 high priority: Ubuntu including 2 source packages (golang-google-grpc, google-guest-agent), 14 status rows across 7 suites (bionic, focal, jammy, noble, questing, upstream, xenial): needs-triage 14. https://ubuntu.com/security/CVE-2026-33186

Affected software / configurations for CVE-2026-33186

Vendor Product Version Raw CPE
grpc grpc < 1.79.3 cpe:2.3:a:grpc:grpc:*:*:*:*:*:go:*:*

References for CVE-2026-33186

cvelogic Threat Intelligence