Live Exposure Defense: From CVE to Confirmed Exposure in 12 Hours – See more

Back
New CVE Detected

CVE-2026-88877 – Authentication Bypass – Traefik v3.7.0 through v3.7.11

Be the first to know when new zero-days emerge:

Subscribe to Email Alerts
Subscribe to RSS Feed

Summary

CVE-2026-88877 is an authentication bypass vulnerability in Traefik’s Kubernetes ingress-nginx provider, affecting deployments that combine authentication annotations with the nginx.ingress.kubernetes.io/from-to-www-redirect directive. A crafted request with a malformed port in the Host header causes Traefik to route the request to a sibling router that lacks the Ingress’s authentication and other annotation-derived middlewares, granting unauthenticated access to the protected backend. The issue is rated critical severity (CVSS 9.3) due to its low complexity and network-exploitable nature.

Technical details

  • Root cause: When an Ingress resource has both an authentication annotation (e.g., basic auth, source-IP allowlisting) and the from-to-www-redirect annotation, Traefik’s Kubernetes ingress-nginx provider generates two routers — one carrying the redirect middleware and one pointing directly at the protected backend — but only the redirect router receives the annotation-derived middlewares.
  • Trigger condition: The redirect-matching logic only recognizes numeric ports, while Traefik’s host matcher normalizes authorities containing non-numeric or empty ports (e.g., Host: www.example.com:x). This mismatch causes such requests to be routed to the sibling router that was never assigned the authentication/allowlist middlewares.
  • Attack vector: Remote, unauthenticated, over the network (HTTP/HTTPS) — requires no credentials, no user interaction, and low attacker complexity.
  • Impact: Complete bypass of authentication and other annotation-based protections (e.g., basic auth, source-IP allowlisting) on the affected route, exposing the backend service to unauthorized access, with high impact to confidentiality, integrity, and availability of the protected resource.

Affected software

  • Traefik Proxy v3.7.0 through v3.7.11 (Kubernetes ingress-nginx provider), when an Ingress combines an authentication annotation with the nginx.ingress.kubernetes.io/from-to-www-redirect annotation.
  • Traefik v2.x and versions prior to v3.7.0 are not affected.

Severity

  • CVSS v3.1: 9.8 (Critical) — CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
  • CVSS v4.0: 9.3 (Critical) — CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
  • CWE-639: Authorization Bypass Through User-Controlled Key

Mitigation and recommended actions

  • Immediate: Upgrade Traefik to v3.7.12 or later, which fixes the router middleware assignment so annotation-derived middlewares apply consistently to both the redirect and protected-backend routers.
  • If patching is not immediately possible:
    • Remove or avoid combining the nginx.ingress.kubernetes.io/from-to-www-redirect annotation with authentication annotations on the same Ingress resource until patched.
    • Enforce authentication and access control at an additional layer (e.g., a network firewall, service mesh, or upstream reverse proxy) in front of Traefik so backend services are not solely reliant on Ingress-annotation-based middleware.
    • Monitor and reject inbound requests containing non-numeric or malformed port values in the Host header at the edge.

References

Are you exposed?

Get a free report of your organization’s exposure to this CVE and threat

  • Mapping of all Assets with this Technology
  • Identification of potentially exposed assets to this CVE
  • Confirmation of verified exploitable assets
Get Exposure Report

How IONIX’s External Exposure Management Platform Detects and Validates
Zero-Days to Shrink MTTR

1

Map your entire attack surface (continously)

IONIX uses multi-factor discovery methods, including DNS analysis, certificate mapping, metadata inspection, and more, to automatically map every internet-facing asset across your environment. This includes cloud instances, third-party platforms, shadow IT, and even forgotten infrastructure that traditional tools miss.

2

Monitor for new CVEs

Dozens of threat intel feeds using agentic technology are continuously analyzed to detect the appearance of proof-of-concept code, exploit kits, and indicators of active targeting. IONIX goes further by applying AI to proactively evaluate whether emerging vulnerabilities are likely to be exploited, even before PoCs go public.

3

Identify Potential External Exposures

Not all CVEs matter. IONIX filters vulnerabilities by asking attacker-centric questions: Can it be reached from the internet? Does it require authentication? Is it being exploited in the wild? This dramatically reduces noise and focuses teams on threats that can actually be weaponized.

4

Create Safe, Scalable Exploit Validations

IONIX transforms real-world PoCs into safe, non-intrusive test payloads that can be run in production environments without disruption. These simulations are precisely targeted to the systems that are vulnerable, ensuring rapid validation without unnecessary load.

5

Execute Exploit Validations

By combining context about software stack, versioning, exposure status, and reachability, IONIX ensures that only the right payloads are executed against the right assets, maximizing efficiency and minimizing risk.

6

Drive Fast and Actionable Remediation

Results are routed through integrations with ticketing, SOAR, and SIEM tools. Issues are written in plain language, bundled into remediation clusters, and prioritized based on asset criticality, exploitability, and blast radius. This shortens mean time to remediation (MTTR) and empowers teams to act with confidence.

Are you exposed?

Get a free report of your organization’s exposure to this CVE and threat

  • Mapping of all Assets with this Technology
  • Identification of potentially exposed assets to this CVE
  • Confirmation of verified exploitable assets
Get Exposure Report
Close

Subscribe to Threat Center RSS

Copy/paste the link below into your preferred RSS reader or follow these instructions to subscribe to Slack alerts.

Open RSS feedSlack setup instructions

Close

Get Real-Time CVE Alerts to Your Email

Be the first to know when new zero-days emerge