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Vulnerability record · CVE-2026-48491 · published 23 June 2026

CVE-2026-48491: Traefik authentication bypass via alternate path vulnerability

Traefik · Traefik

Traefik is an HTTP reverse proxy and load balancer. From 3.7.0 until 3.7.3, there is a high severity vulnerability in Traefik's domain-fronting protection (SNICheck) that allows an unauthenticated client to bypass mutual TLS enforced through wildcard router TLSOptions. When a router uses a wildcard host rule such as Host(*.example.com) with stricter TLS options (for example RequireAndVerifyClientCert), SNICheck resolves the TLS options for the HTTP Host header using exact map lookups only and never applies wildcard matching. If another permissive SNI is served on the same entrypoint, an attacker can complete the TLS handshake under the permissive options and then send an HTTP Host header targeting the wildcard-protected backend, reaching it without presenting a client certificate. This affects the regular HTTPS / HTTP-2 path and does not require HTTP/3. This vulnerability is fixed in 3.7.3.

7.8 CVSS 4.0 High EPSS 0.36% · top 73.1% CWE-288 · Authentication bypass via alternate pathCWE-807 · CWE-807
7.8CVSS 4.0 base score
0.36%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
6References, 1 tagged exploit
2 Sep 2026Last modified by NVD

Description

Traefik is an HTTP reverse proxy and load balancer. From 3.7.0 until 3.7.3, there is a high severity vulnerability in Traefik's domain-fronting protection (SNICheck) that allows an unauthenticated client to bypass mutual TLS enforced through wildcard router TLSOptions. When a router uses a wildcard host rule such as Host(*.example.com) with stricter TLS options (for example RequireAndVerifyClientCert), SNICheck resolves the TLS options for the HTTP Host header using exact map lookups only and never applies wildcard matching. If another permissive SNI is served on the same entrypoint, an attacker can complete the TLS handshake under the permissive options and then send an HTTP Host header targeting the wildcard-protected backend, reaching it without presenting a client certificate. This affects the regular HTTPS / HTTP-2 path and does not require HTTP/3. This vulnerability is fixed in 3.7.3.

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

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://github.com/traefik/traefik/releases/tag/v3.7.3 PatchRelease Notes
https://github.com/traefik/traefik/security/advisories/GHSA-5r4w-85f3-pw66 ExploitMailing ListPatchVendor Advisory
https://access.redhat.com/errata/RHSA-2026:62260
https://access.redhat.com/security/cve/CVE-2026-48491
https://bugzilla.redhat.com/show_bug.cgi?id=2491923
https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-48491.json

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

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Source: NIST National Vulnerability Database (record CVE-2026-48491), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.