9.8
CRITICAL CVSS 3.1
CVE-2026-88877
Traefik v3.7.0 Authentication Bypass via from-to-www-redirect
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.

INFO

Published Date :

Sept. 10, 2026, 2:17 p.m.

Last Modified :

Sept. 10, 2026, 3:17 p.m.

Remotely Exploit :

Yes !
Affected Products

The following products are affected by CVE-2026-88877 vulnerability. Even if cvefeed.io is aware of the exact versions of the products that are affected, the information is not represented in the table below.

No affected product recoded yet

CVSS Scores
The Common Vulnerability Scoring System is a standardized framework for assessing the severity of vulnerabilities in software and systems. We collect and displays CVSS scores from various sources for each CVE.
Score Version Severity Vector Exploitability Score Impact Score Source
CVSS 134c704f-9b21-4f2e-91b3-4a467353bcc0
CVSS 3.1 CRITICAL 83251b91-4cc7-4094-a5c7-464a1b83ea10
CVSS 3.1 CRITICAL [email protected]
CVSS 4.0 CRITICAL 83251b91-4cc7-4094-a5c7-464a1b83ea10
CVSS 4.0 CRITICAL [email protected]
Solution
Update Traefik to version v3.7.12 or later to fix the ingress-nginx provider mishandling.
  • Update Traefik to version v3.7.12 or later.
  • Verify ingress-nginx provider configuration for affected Ingresses.
  • Test authentication and middleware functionality after update.
References to Advisories, Solutions, and Tools

Here, you will find a curated list of external links that provide in-depth information, practical solutions, and valuable tools related to CVE-2026-88877.

URL Resource
https://github.com/traefik/traefik/security/advisories/GHSA-cjr6-pf59-jq29
https://www.vulncheck.com/advisories/traefik-3.7.0-authentication-bypass-via-from-to-www-redirect
CWE - Common Weakness Enumeration

While CVE identifies specific instances of vulnerabilities, CWE categorizes the common flaws or weaknesses that can lead to vulnerabilities. CVE-2026-88877 is associated with the following CWEs:

Common Attack Pattern Enumeration and Classification (CAPEC)

Common Attack Pattern Enumeration and Classification (CAPEC) stores attack patterns, which are descriptions of the common attributes and approaches employed by adversaries to exploit the CVE-2026-88877 weaknesses.

We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).

Results are limited to the first 15 repositories due to potential performance issues.

The following list is the news that have been mention CVE-2026-88877 vulnerability anywhere in the article.

The following table lists the changes that have been made to the CVE-2026-88877 vulnerability over time.

Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.

  • CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0

    Sep. 10, 2026

    Action Type Old Value New Value
    Added SSVC {'id': 'CVE-2026-88877', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'none'}, {'automatable': 'yes'}, {'technicalImpact': 'total'}], 'version': '2.0.3', 'timestamp': '2026-09-10T14:09:57.234385Z'}
  • New CVE Received by [email protected]

    Sep. 10, 2026

    Action Type Old Value New Value
    Added 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.
    Added CVSS V4.0 AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
    Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
    Added CWE CWE-639
    Added Affected New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/88xxx/CVE-2026-88877.json">CVE-2026-88877</a>
    Added Reference https://github.com/traefik/traefik/security/advisories/GHSA-cjr6-pf59-jq29
    Added Reference https://www.vulncheck.com/advisories/traefik-3.7.0-authentication-bypass-via-from-to-www-redirect
EPSS is a daily estimate of the probability of exploitation activity being observed over the next 30 days. Following chart shows the EPSS score history of the vulnerability.