# CVE-2026-88877: Traefik v3.7.0 Authentication Bypass via from-to-www-redirect

> Attackers can bypass authentication and other security middlewares in Traefik Kubernetes ingress-nginx provider by exploiting a routing flaw with www-redirect annotations.

- **Severity:** Critical 9.3 (`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`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 10 Sep 2026
- **Updated:** 8 Oct 2026
- **Also known as:** GHSA-9rch-gvf7-hrfc, GHSA-cjr6-pf59-jq29, MINI-8xm8-r3jf-gr3g, MINI-pm8f-62qf-mwvv

## What is CVE-2026-88877?

CVE-2026-88877 is a critical authentication bypass vulnerability in Traefik Traefik, published on 10 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Traefik is a HTTP reverse proxy and load balancer. In versions >= v3.7.0 and <= v3.7.11, the Kubernetes ingress-nginx provider mishandles Ingresses that carry both an authentication annotation and the nginx.ingress.kubernetes.io/from-to-www-redirect annotation. For such Ingresses the provider creates an additional 'sibling' router that matches on the host alone, carries only the RedirectRegex middleware, and still points at the parent router's protected backend service. Because RedirectRegex is not a terminal handler, a request its pattern does not match is forwarded to the backend, and because the redirect pattern only accepts a numeric port while Traefik's host matcher canonicalizes the authority via net.SplitHostPort, a request with a non-numeric or empty port (for example 'Host: www.example.com:x') selects the sibling router, misses the redirect, and is proxied to the protected backend with none of the Ingress's annotation-derived middlewares applied. This discards not only authentication (e.g. BasicAuth) but every annotation-derived middleware, including source-IP allowlisting. Traefik v2 and v3 releases before v3.7.0 are not affected. The issue is fixed in v3.7.12.

Weakness: CWE-639 (Authorization Bypass Through User-Controlled Key)

## Which versions are affected by CVE-2026-88877?

It affects 1 product.


Products: Traefik Traefik.

## How do I fix CVE-2026-88877?

Upgrade to a fixed version.

## Is CVE-2026-88877 being exploited?

There is no known exploitation of CVE-2026-88877 in the wild and no public exploit code.

Public exploit code:

- https://github.com/pwnVader/CVE-2026-88877-PoC-pwnVader (github_poc): https://github.com/pwnVader/CVE-2026-88877-PoC-pwnVader

## Other vulnerabilities in Traefik Traefik

- [CVE-2024-45410](https://insights.sbomify.com/CVE-2024-45410/): HTTP client can remove the X-Forwarded headers in Traefik (critical 9.8)
- [CVE-2026-85595](https://insights.sbomify.com/CVE-2026-85595/): Traefik before v2.11.55 and v3.0.0 through v3.7.10 Authentication Bypass via digestAuth (critical 9.3)
- [CVE-2026-88007](https://insights.sbomify.com/CVE-2026-88007/): Traefik HTTP/3 Backend NTLM Connection Reuse (critical 9.1)
- [CVE-2026-88009](https://insights.sbomify.com/CVE-2026-88009/): Traefik: Rootless HTTP/1 request-target routes as "/" but is forwarded verbatim, bypassing path-scoped routing, middleware guards and access logging (high 8.8)
- [CVE-2025-32431](https://insights.sbomify.com/CVE-2025-32431/): Traefik has a possible vulnerability with the path matchers (high 8.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-88877 and fix it if it is affected.

What it is: CVE-2026-88877 is a critical authentication bypass vulnerability in Traefik Traefik, published on 10 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-88877 in the wild and no public exploit code.

Affected product: Traefik Traefik. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-88877/ (Markdown: https://insights.sbomify.com/CVE-2026-88877/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-88877
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-88877
- OSV: https://osv.dev/vulnerability/CVE-2026-88877

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-88877/
Summaries are generated and may contain mistakes; the official description above is the record.