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TraefikApplication

CVE-2026-48491

CRITICAL · 10.0 CVSS v3.1 Published 2026-06-23
Fix available
A fix is available. Upgrade to 3.7.3 or later.
See remediation →
100/100
Remediation priority · Urgent
Public exploit Remotely reachable No privileges Zero-click Patch available

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

In Traefik 3.7.0-3.7.3, the SNICheck domain-fronting protection fails to apply wildcard matching when resolving TLS options for HTTP Host headers. When a router uses wildcard host rules (e.g., Host(*.example.com)) with strict TLS options like RequireAndVerifyClientCert, the system uses exact map lookups only. An attacker on the same entrypoint with a permissive SNI can complete the TLS handshake under permissive options, then send an HTTP Host header targeting the wildcard-protected backend to access it without presenting a client certificate.

MitigationUpgrade Traefik to version 3.7.3 or later. Until then, avoid sharing entrypoints between wildcard-protected and permissive routers, or implement additional authentication layers.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
TraefikApplication
Affected:>= 3.7.0, < 3.7.3

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Changed
Confidentiality
High
Integrity
High
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Check Traefik version
    Run 'traefik version' or check the container/image version to identify the installed version of Traefik
    Affected if The installed version is >= 3.7.0 and < 3.7.3
  2. Identify wildcard host rule configurations
    Review your router configurations in static and dynamic configuration files for rules using the pattern Host(*.example.com) or similar wildcard host matching
    Affected if Routers are configured with wildcard host rules such as Host(*.domain.com)
  3. Verify TLS options configuration
    Examine your TLS options or router TLS configuration for the presence of RequireAndVerifyClientCert or strict client certificate requirements
    Affected if TLS options are set to RequireAndVerifyClientCert or other strict mTLS settings on routers with wildcard hosts
  4. Check entrypoint sharing
    Inspect your entrypoint definitions and identify whether multiple routers with different TLS strictness levels share the same entrypoint
    Affected if The same entrypoint is used by both routers with permissive TLS and routers with strict TLS options like RequireAndVerifyClientCert

You are affected if your Traefik version is between 3.7.0 and 3.7.3, you use wildcard host rules with strict TLS options like RequireAndVerifyClientCert, and those routers share an entrypoint with less restrictive TLS configurations.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 3.7.3 or later
Fixed in 3.7.3
Vendor patch github.com →
Interim mitigation

Upgrade Traefik to version 3.7.3 or later. Until then, avoid sharing entrypoints between wildcard-protected and permissive routers, or implement additional authentication layers.

Recommended fix High confidence

Traefik 3.7.3

  1. Backup your current Traefik configuration and deployment
  2. Upgrade Traefik from your current 3.7.x version to version 3.7.3
  3. Verify the upgrade was successful by checking the Traefik version
  4. Test that mutual TLS (RequireAndVerifyClientCert) is now properly enforced for wildcard host rules like Host(*.example.com)
  5. Confirm the SNICheck is correctly applying TLS options via wildcard matching

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Traefik Scoped from the published advisory
  • Consultation2.0 h
  • Implementation2.0 h
  • Testing3.0 h
  • Review / QA1.0 h
8.0 hours of engineering $1,390
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,224.

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-48491 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data