VulnerabilityPublished 24 Apr 2026Updated 6 May 2026

CVE-2026-41174: V3 · Traefik Kubernetes CRD allows unauthorized cross-namespace middleware binding

Affects github.com/traefik/traefik/v3Source GCVE Database

Authoritative record:CVE-2026-41174· Medium 4.8

Not known to be exploited · CVSS 4.8 Medium : upgrade to 3.7.0-rc.2 when convenient.

Data as of 27 Oct 2026, 00:07 UTC

CVSS 4.0 base score

4.8Medium

How severe the flaw is on the 0–10 CVSS scale.

Patch: Available – fixed in 3.7.0-rc.2, 3.6.14, 2.11.43

CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N

Attack Vector: Local
Attack Complexity: Low
Attack Requirements: None
Privileges Required: Low
User Interaction: None
Vulnerable system confidentiality: None
Vulnerable system integrity: None
Vulnerable system availability: None
Subsequent system confidentiality: Low
Subsequent system integrity: Low
Subsequent system availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Local: The vulnerable system is not bound to the network stack and the attacker’s path is via read/write/execute capabilities. Either the attacker exploits the vulnerability by accessing the target system locally (e.g., keyboard, console), or through terminal emulation (e.g., SSH); or the attacker relies on User Interaction by another person to perform actions required to exploit the vulnerability (e.g., using social engineering techniques to trick a legitimate user into opening a malicious document).
Attack Complexity: Low: The attacker must take no measurable action to exploit the vulnerability. The attack requires no target-specific circumvention to exploit the vulnerability. An attacker can expect repeatable success against the vulnerable system.
Attack Requirements: None: The successful attack does not depend on the deployment and execution conditions of the vulnerable system. The attacker can expect to be able to reach the vulnerability and execute the exploit under all or most instances of the vulnerability.
Privileges Required: Low: The attacker requires privileges that provide basic capabilities that are typically limited to settings and resources owned by a single low-privileged user. Alternatively, an attacker with Low privileges has the ability to access only non-sensitive resources.
User Interaction: None: The vulnerable system can be exploited without interaction from any human user, other than the attacker.
Vulnerable system confidentiality: None: There is no loss of confidentiality within the Vulnerable System.
Vulnerable system integrity: None: There is no loss of integrity within the Vulnerable System.
Vulnerable system availability: None: There is no impact to availability within the Vulnerable System.
Subsequent system confidentiality: Low: There is some loss of confidentiality. Access to some restricted information is obtained, but the attacker does not have control over what information is obtained, or the amount or kind of loss is limited. The information disclosure does not cause a direct, serious loss to the Subsequent System.
Subsequent system integrity: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact to the Subsequent System.
Subsequent system availability: None: There is no impact to availability within the Subsequent System or all availability impact is constrained to the Vulnerable System.

Definitions: FIRST CVSS v4.0 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 30 Apr 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
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), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade github.com/traefik/traefik/v3 to 3.7.0-rc.2; github.com/traefik/traefik/v3 to 3.6.14; github.com/traefik/traefik/v2 to 2.11.43.

Affected software

Product	Affected	Fixed in
Gogithub.com/traefik/traefik/v3	Affected >=3.7.0-ea.1 <3.7.0-rc.2	Fixed in 3.7.0-rc.2
Gogithub.com/traefik/traefik/v3	Affected >=3.0.0-beta1 <3.6.14	Fixed in 3.6.14
Gogithub.com/traefik/traefik/v2	Affected <2.11.43	Fixed in 2.11.43
Gogithub.com/traefik/traefik	Affected <=1.7.34	Fixed in–

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

Description

## Summary There is a vulnerability in Traefik's Kubernetes CRD provider cross-namespace isolation enforcement. When `providers.kubernetesCRD.allowCrossNamespace=false`, Traefik correctly rejects direct cross-namespace middleware references from `IngressRoute` objects, but fails to apply the same restriction to middleware references nested inside a `Chain` middleware's `spec.chain.middlewares[]`. An actor with permission to create or update Traefik CRDs in their own namespace can exploit this to cause Traefik to resolve and apply middleware objects from another namespace, bypassing the documented isolation boundary. ## Patches - https://github.com/traefik/traefik/releases/tag/v2.11.43 - https://github.com/traefik/traefik/releases/tag/v3.6.14 - https://github.com/traefik/traefik/releases/tag/v3.7.0-rc.2 ## For more information If there are any questions or comments about this advisory, please [open an issue](https://github.com/traefik/traefik/issues). <details> <summary>Original Description</summary> ### Summary When `providers.kubernetesCRD.allowCrossNamespace=false`, Traefik still allows a namespace-local `Middleware` of type `Chain` to reference middleware objects from another namespace via `spec.chain.middlewares[].namespace`. This bypasses the documented cross-namespace restriction and allows an actor with permission to create or update Traefik CRDs in namespace A to bind middleware defined in namespace B to routes in namespace A. ### Details Traefik documents `allowCrossNamespace` as the control that governs whether `IngressRoute` objects may reference resources in other namespaces. Direct middleware references from `IngressRoute.routes[].middlewares[]` are validated in `pkg/provider/kubernetes/crd/kubernetes_http.go` by `makeMiddlewareKeys(...)`, which rejects cross-namespace references when `allowCrossNamespace` is disabled. However, nested middleware references inside `Middleware.spec.chain.middlewares[]` follow a different code path. `createChainMiddleware(...)` in `pkg/provider/kubernetes/crd/kubernetes.go` does not receive or enforce `allowCrossNamespace`; it resolves `mi.Namespace` (or defaults to the current namespace) and appends `makeID(ns, mi.Name)` unconditionally. At runtime, `pkg/server/middleware/middlewares.go` qualifies and builds `config.Chain.Middlewares`, so the cross-namespace middleware is actually loaded and used. This was verified on the current `master` at commit `786f7192e11878dfaa634f8263bf79bb730a71cb`. This appears related to earlier cross-namespace hardening work, but the surviving issue is a distinct nested `Chain` middleware code path rather than the already-guarded direct reference path. ### Expected behavior When `providers.kubernetesCRD.allowCrossNamespace=false`, any middleware reference that resolves to an object in another namespace should be rejected, whether referenced directly from an `IngressRoute` or indirectly through a local `Chain` middleware. ### Actual behavior A namespace-local `Chain` middleware can reference `spec.chain.middlewares[].namespace` in another namespace, and Traefik resolves and applies that middleware even when cross-namespace references are disabled. ### Attacker prerequisites The attacker must have permission to create or update Traefik CRDs in a namespace they control, but does not need permission to modify resources in the target namespace. ### PoC 1. Run Traefik with the Kubernetes CRD provider and set `allowCrossNamespace: false`. 2. Create two namespaces, for example `default` and `cross-ns`. 3. Apply a middleware in `cross-ns`: ```yaml apiVersion: traefik.io/v1alpha1 kind: Middleware metadata: name: victim-strip namespace: cross-ns spec: stripPrefix: prefixes: - /secret ``` 4. Apply a chain middleware in `default` that references the middleware above: ```yaml apiVersion: traefik.io/v1alpha1 kind: Middleware metadata: name: mychain namespace: default spec: chain: middlewares: - name: victim-strip namespace: cross-ns ``` 5. Apply an `IngressRoute` in `default` that references only the local `mychain` middleware: ```yaml apiVersion: traefik.io/v1alpha1 kind: IngressRoute metadata: name: demo namespace: default spec: entryPoints: - web routes: - match: Host(`example.test`) && PathPrefix(`/demo`) kind: Rule middlewares: - name: mychain services: - name: whoami port: 80 ``` 6. Observe that Traefik accepts the configuration and resolves the resulting chain to the middleware from `cross-ns` even though `allowCrossNamespace` is disabled. 7. As a control, replace the local chain reference in the `IngressRoute` with a direct cross-namespace middleware reference. That direct reference is rejected when `allowCrossNamespace=false`, which indicates the bypass is specific to nested `Chain` middleware resolution. ### Impact This is an authorization / trust-boundary bypass in Traefik's Kubernetes CRD provider. Clusters t

CWE-653Improper Isolation or Compartmentalization (opens in a new tab)
Class weaknessOWASP Top 10 A06:2025: Insecure Design (opens in a new tab)
The product does not properly compartmentalize or isolate functionality, processes, or resources that require different privilege levels, rights, or permissions.
Architecture and Design
Break up privileges between different modules, objects, or entities. Minimize the interfaces between modules and require strong access control between them.
OWASP Cheat Sheets
Secure Design Principles (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).
CWE-863Incorrect Authorization (opens in a new tab)
Class weaknessLikelihood of exploit: HighCWE Top 25 (2025): #17OWASP Top 10 A01:2025: Broken Access Control (opens in a new tab)
The product performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check.
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.
Architecture and Design
Ensure that access control checks are performed related to the business logic. These checks may be different than the access control checks that are applied to more generic resources such as files, connections, processes, memory, and database records.
Architecture and Design · Libraries or Frameworks
Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
OWASP Cheat Sheets
Authorization (opens in a new tab)
OWASP ASVS 4.0.3
V8.3.8 (opens in a new tab)
V13.4.2 (opens in a new tab)
V7.2.2 (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

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Exploitation evidence

What to do

Affected software

Description

WeaknessesCWE-653, CWE-863

Technical details

References

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