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Public proof of conceptFix available

CVE-2026-33186

A public proof of concept exists; no exploitation attested.

  • Published2026-03-20
  • Fixed in1.79.3
  • WeaknessCWE-285 · CWE-551

Am I affected?

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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.

Timeline

dates in UTC
  1. 2026-03-2023:16CVE publishedNVD
  2. 2026-10-2319:23First public proof of conceptPoC-in-GitHub

Observed activity

isMalicious corpus · updated 2026-10-23 21:37 UTC
Indicators tagged with this CVE, per day0 indicators over 7 days
Block these indicators
  • Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2026-33186?format=txt
  • CSV export: https://api.ismalicious.com/edl/cve/CVE-2026-33186?format=csv
  • TAXII collection of exploited CVEs
  • The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD · OSV
Grpc
BranchAffectedFixed in
1.79< 1.79.31.79.3

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Distribution builds and vendor advisories

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Packages

  • opentelemetry-collectorAlmaLinux:10all versions · fixed in 0.144.0-2.el10_2
  • opentelemetry-collectorAlmaLinux:9all versions · fixed in 0.144.0-2.el9_8
  • osbuild-composerAlmaLinux:8all versions · fixed in 101.5-1.el8_10.alma.1and 2 other packages

Vendor advisories

  • RHSA-2026:85846 Red Hat Product Security1 product fixed

    Red Hat Security Advisory: Migration Toolkit for Containers (MTC) 1.8.18 security and bug fix update

  • RHSA-2026:79154 Red Hat Product Security4 products fixed

    Red Hat Security Advisory: OpenShift Container Platform 4.22.18 bug fix and security update

  • RHSA-2026:83627 Red Hat Product Security64 products fixed

    Red Hat Security Advisory: Red Hat OpenShift Data Foundation 4.14.40 security, enhancement & bug fix update

  • RHSA-2026:83622 Red Hat Product Security68 products fixed

    Red Hat Security Advisory: Red Hat OpenShift Data Foundation 4.17.28 security, enhancement & bug fix update

  • RHSA-2026:83619 Red Hat Product Security64 products fixed

    Red Hat Security Advisory: Red Hat OpenShift Data Foundation 4.16.36 security, enhancement & bug fix update

  • RHSA-2026:77321 Red Hat Product Security2 products fixed

    Red Hat Security Advisory: OpenShift Container Platform 4.13.72 bug fix and security update

94 more advisories

Full record on NVD

Fix

  1. Update Grpc to 1.79.3
  2. Vendor fix Red Hat Product Security RHSA-2026:85846 · 1 productBefore applying this update, make sure all previously released errata relevant to your system have been applied.
  3. Vendor fix Red Hat Product Security RHSA-2026:79154 · 4 productsFor OpenShift Container Platform 4.22 see the following documentation, which will be updated shortly for this release, for important instructions on how to upgrade your cluster and fully apply this asynchronous errata update: https://docs.redhat.com/en/documentation/openshift_container_platform/4.…
  4. Vendor fix Red Hat Product Security RHSA-2026:83627 · 64 productsBefore applying this update, make sure all previously released errata relevant to your system have been applied. For details on how to apply this update, refer to: https://docs.redhat.com/en/documentation/red_hat_openshift_data_foundation/4.14/html/updating_openshift_data_foundation/updating-ocs-…
  5. Vendor fix Red Hat Product Security RHSA-2026:83622 · 68 productsBefore applying this update, make sure all previously released errata relevant to your system have been applied. For details on how to apply this update, refer to: https://docs.redhat.com/en/documentation/red_hat_openshift_data_foundation/4.17/html/updating_openshift_data_foundation/updating-ocs-…
  6. Vendor fix Red Hat Product Security RHSA-2026:83619 · 64 productsBefore applying this update, make sure all previously released errata relevant to your system have been applied. For details on how to apply this update, refer to: https://docs.redhat.com/en/documentation/red_hat_openshift_data_foundation/4.16/html/updating_openshift_data_foundation/updating-ocs-…
  7. Vendor fix Red Hat Product Security RHSA-2026:77321 · 2 productsFor OpenShift Container Platform 4.13 see the following documentation, which will be updated shortly for this release, for important instructions on how to upgrade your cluster and fully apply this asynchronous errata update: https://docs.redhat.com/en/documentation/openshift_container_platform/4.…

Advisories and patches

Detection

read 2026-10-23 19:25 UTC
Nuclei template
none so far
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Proof-of-concept repositories
1 repository, unverifiedJohannesLks/CVE-2026-33186
PoC-in-GitHub

Sources

  • NVDCVE recordread 2026-10-23
  • CISA-ADPSSVC decisionnone2026-03-24
  • OpenCVESSVC decisionnone—
  • CNACVSS 3.19.1read 2026-10-23
  • CNAweakness (CWE)CWE-285, CWE-551read 2026-10-23
  • FIRST EPSSEPSS score1.6 %2026-10-22
  • PoC-in-GitHubproof of concept1read 2026-10-23
  • OSVaffected packages—

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Published
2026-03-20
Last Modified
2026-09-18
NVD status
Modified

Frequently asked questions

What is CVE-2026-33186?

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.

Is CVE-2026-33186 actively exploited?

Active exploitation of CVE-2026-33186 has not been confirmed. Its EPSS score was 1.6% on 2026-10-22, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2026-33186?

CVE-2026-33186 has a CVSS v3 base score of 9.1 (CRITICAL severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N.

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