CVE-2026-48491
Description
A flaw was found in Traefik, an HTTP reverse proxy and load balancer. This vulnerability allows an unauthenticated client to bypass mutual Transport Layer Security (TLS) enforcement, a security measure that verifies both client and server identities. The bypass occurs due to an issue in Traefik's domain-fronting protection (SNICheck), which incorrectly processes TLS options for HTTP Host headers. As a result, an attacker can gain unauthorized access to protected backend services without presenting a required client certificate.
Statement
This is an Important flaw in Traefik that allows an unauthenticated client to bypass mutual TLS authentication. The vulnerability arises from an issue in Traefik's domain-fronting protection when specific wildcard host rules with strict TLS options are used alongside permissive SNI configurations on the same entrypoint. This bypass enables unauthorized access to protected backend services, undermining critical access controls.
Mitigation
To mitigate this issue, avoid configuring Traefik with wildcard host rules (e.g., Host(*.example.com)) alongside strict TLS options such as RequireAndVerifyClientCert on entrypoints that also serve permissive SNI configurations. Alternatively, restrict network access to Traefik's entrypoints to trusted networks only, thereby limiting potential exposure.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 9.1 | 10 | 9.1 |
| Attack Vector | Network | Network | Network |
| Attack Complexity | Low | Low | Low |
| Privileges Required | None | None | None |
| User Interaction | None | None | None |
| Scope | Unchanged | Changed | Unchanged |
| Confidentiality | High | High | High |
| Integrity Impact | High | High | High |
| Availability Impact | None | None | None |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
NVD: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N
cve.org: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Understanding the Weakness (CWE)
Confidentiality,Access Control,Availability,Other
Technical Impact: Bypass Protection Mechanism; Gain Privileges or Assume Identity; Varies by Context
Attackers can bypass the security decision to access whatever is being protected. The consequences will depend on the associated functionality, but they can range from granting additional privileges to untrusted users to bypassing important security checks. Ultimately, this weakness may lead to exposure or modification of sensitive data, system crash, or execution of arbitrary code.
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