GHSA-46wh-3698-f2cx GO-2026-4897
Traefik: Deny Rule Bypass via Unauthenticated Malicious gRPC Requests in gRPC-Go Dependency (CVE-2026-33186)
- Severity
- 0.0 / 10
- High · CVSS 4.0
- Exploit chance (EPSS)
- —
- No score published
- Known exploited
- No
- Not in CISA's catalog
- Fix
- Available
- 2 packages have a fixed version
Description
Summary
There is a potential vulnerability in Traefik due to its dependency on an affected version of gRPC-Go (CVE-2026-33186).
A remote, unauthenticated attacker can send gRPC requests with a malformed HTTP/2 :path pseudo-header omitting the mandatory leading slash (e.g., Service/Method instead of /Service/Method). While the server routes such requests correctly, path-based authorization interceptors evaluate the raw non-canonical path and fail to match "deny" rules, allowing the request to bypass the policy entirely if a fallback "allow" rule is present.
Patches
- https://github.com/traefik/traefik/releases/tag/v2.11.42
- https://github.com/traefik/traefik/releases/tag/v3.6.12
- https://github.com/traefik/traefik/releases/tag/v3.7.0-ea.3
For more information
If there are any questions or comments about this advisory, please open an issue.
<details> <summary>Original Description</summary>
Summary
This CVE hits traefik until Version 3.6.11 and 2.11.41. gRPC-Go has an authorization bypass via missing leading slash in :path
Details
As described in https://github.com/advisories/GHSA-p77j-4mvh-x3m3
PoC
Update library version in https://github.com/traefik/traefik/blob/67c64ed9b25fbb90f1086977a62827133a7aa01b/go.mod#L108
Impact
Is described in https://github.com/advisories/GHSA-p77j-4mvh-x3m3
</details>
Affected versions
Go
| Package | Vulnerable | Fixed in |
|---|---|---|
| github.com/traefik/traefik | all versions |
No fix yet |
| github.com/traefik/traefik/v2 | < 2.11.42 |
2.11.42 |
| github.com/traefik/traefik/v3 | >= 3.0.0-beta3, < 3.6.12 |
3.6.12 |
| github.com/traefik/traefik/v3 | >= 3.7.0-ea.1, < 3.7.0-ea.3 |
3.7.0-ea.3 |
| github.com/traefik/traefik/v3 | >= 3.0.0-beta3, < 3.6.12>= 3.7.0-ea.1, < 3.7.0-ea.3 |
3.6.123.7.0-ea.3 |
How to fix
Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.
github.com/traefik/traefik/v2 Go → 2.11.42
- go
go get github.com/traefik/traefik/v2@v2.11.42 && go mod tidy
github.com/traefik/traefik/v3 Go → 3.6.12
- go
go get github.com/traefik/traefik/v3@v3.6.12 && go mod tidy
Severity breakdown
CVSS 4.0 0.0
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/SA:N
- Attack vector
- Network
- Attack complexity
- Low
- Attack requirements
- None
- Privileges required
- None
- User interaction
- None
- Confidentiality (vulnerable system)
- None
- Integrity (vulnerable system)
- None
- Availability (vulnerable system)
- None
- Confidentiality (subsequent systems)
- High
- Integrity (subsequent systems)
- High
- Availability (subsequent systems)
- None
Weakness
CWE-1395: Dependency on Vulnerable Third-Party Component
The product has a dependency on a third-party component that contains one or more known vulnerabilities.
How to prevent it
- Requirements, Policy: In some industries such as healthcare [REF-1320] [REF-1322] or technologies such as the cloud [REF-1321], it might be unclear about who is responsible for applying patches for third-party vulnerabilities: the vendor, the operator/customer, or a separate service. Clarifying roles and responsibilities can be important to minimize confusion or unnecessary delay when third-party vulnerabilities are disclosed.
- Requirements: Require a Bill of Materials for all components and sub-components of the product. For software, require a Software Bill of Materials (SBOM) [REF-1247] [REF-1311].
- Architecture and Design, Implementation, Integration, Manufacturing: Maintain a Bill of Materials for all components and sub-components of the product. For software, maintain a Software Bill of Materials (SBOM). According to [REF-1247], "An SBOM is a formal, machine-readable inventory of software components and dependencies, information about those components, and their hierarchical relationships."
- Operation, Patching and Maintenance: Actively monitor when a third-party component vendor announces vulnerability patches; fix the third-party component as soon as possible; and make it easy for operators/customers to obtain and apply the patch.
- Operation, Patching and Maintenance: Continuously monitor changes in each of the product's components, especially when the changes indicate new vulnerabilities, end-of-life (EOL) plans, etc.
CWE-285: Improper Authorization
The product does not perform or incorrectly performs an authorization check when an actor attempts to access a resource or perform an action.
How to prevent it
- Architecture and Design: Divide the product into anonymous, normal, privileged, and administrative areas. Reduce the attack surface by carefully mapping roles with data and functionality. Use role-based access control (RBAC) to enforce the roles at the appropriate boundaries. Note that this approach may not protect against horizontal authorization, i.e., it will not protect a user from attacking others with the same role.
- Architecture and Design: Ensure that you perform access control checks related to your business logic. These checks may be different than the access control checks that you apply to more generic resources such as files, connections, processes, memory, and database records. For example, a database may restrict access for medical records to a specific database user, but each record might only be intended to be accessible to the patient and the patient's doctor.
- Architecture and Design: Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. For example, consider using authorization frameworks such as the JAAS Authorization Framework [REF-233] and the OWASP ESAPI Access Control feature [REF-45].
- Architecture and Design: For web applications, make sure that the access control mechanism is enforced correctly at the server side on every page. Users should not be able to access any unauthorized functionality or information by simply requesting direct access to that page. One way to do this is to ensure that all pages containing sensitive information are not cached, and that all such pages restrict access to requests that are accompanied by an active and authenticated session token associated with a user who has the required permissions to access that page.
- System Configuration, Installation: Use the access control capabilities of your operating system and server environment and define your access control lists accordingly. Use a "default deny" policy when defining these ACLs.
References
Advisories
Packages
Other links
Timeline
- Published
- Last updated by the source
Related advisories
| Advisory | Severity | Why it's related |
|---|---|---|
| GO-2026-6558 Traefik: BasicAuth singleflight coalescing reintroduces an unauthenticated username-enumeration timing oracle | Medium | Also affects github.com/traefik/traefik |
| GHSA-f52w-8j3h-j724 Traefik: Rootless HTTP/1 request-target routes as "/" but is forwarded verbatim, bypassing path-scoped routing, middleware guards and access logging | High | Also affects github.com/traefik/traefik |
| GHSA-w4v4-9rw7-5326 Traefik: Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling') and Incorrect Authorization | Critical | Also affects github.com/traefik/traefik |
| GHSA-qqjf-53cj-pwvv Traefik HTTP/3 Backend NTLM Connection Reuse | Critical | Also affects github.com/traefik/traefik |
| GO-2026-6467 Traefik entrypoint header-name sanitization bypassed via request trailers | High | Also affects github.com/traefik/traefik |
| GHSA-rf44-j88r-hh8c Traefik: ForwardAuth identity spoofing via dot-form header alias | High | Also affects github.com/traefik/traefik |
| GHSA-7ghq-v6jf-g56c Traefik: respondingTimeouts.readTimeout is not applied to HTTP/3, leaving slow-body uploads unbounded | Medium | Also affects github.com/traefik/traefik |
| GHSA-62fc-8686-hfmq Traefik: `allowCrossNamespace=false` bypass via `@kubernetescrd` TraefikService backendRef | Medium | Also affects github.com/traefik/traefik |
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