Traefik: SNICheck ignores wildcard TLSOptions mappings, allowing domain-fronted mTLS bypass

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

7.8 · 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 · score source

EPSS

• CVE-2026-48491: 0.36% estimated exploitation activity in the next 30 days; percentile 29.50 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary 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. Patches - https://github.com/traefik/traefik/releases/tag/v3.7.3 For more information If you have any questions or comments about this advisory, please open an issue. <details <summaryOriginal…

Published by the source

11 Aug 2026, 20:19 UTC

Last modified by the source

2 Sep 2026, 15:34 UTC

Source last checked

26 Oct 2026, 15:28 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-5r4w-85f3-pw66

2. Revision 2 · amended · 25 Oct 2026

   Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

3. Revision 1 · created · 24 Oct 2026

   Published from osv record GO-2026-5152

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# Patch Next advisory brief: CVE-2026-48491

Advisory: Traefik: SNICheck ignores wildcard TLSOptions mappings, allowing domain-fronted mTLS bypass
IDs: CVE-2026-48491, GHSA-5r4w-85f3-pw66
Record: https://patchnext.com/advisories/cve-2026-48491 (revision 3, source checked 26 Oct 2026, 15:28 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.8)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/traefik/traefik/v3 3.7.3; github.com/traefik/traefik/v2 2.11.48. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/traefik/traefik/v3: affected >= 3.7.0, < 3.7.3; fixed in 3.7.3
- Go github.com/traefik/traefik/v2: affected < 2.11.48; fixed in 2.11.48

## Suggested inspection (read-only)
- Go github.com/traefik/traefik/v3: check the installed version with your package manager.
- Go github.com/traefik/traefik/v2: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/traefik/traefik/v3, github.com/traefik/traefik/v2.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GO-2026-5152 (OSV record GO-2026-5152 lists affected ranges: Go github.com/traefik/traefik/v2 >=0 =3.7.0 <3.7.3 (fixed))
- Verified: https://github.com/advisories/GHSA-5r4w-85f3-pw66 (GitHub-reviewed advisory GHSA-5r4w-85f3-pw66 lists affected ranges: Go github.com/traefik/traefik/v2 >=0 =3.7.0 <3.7.3)

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