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CVE Record

CVE-2026-48491: Traefik: SNICheck ignores wildcard TLSOptions mappings, allowing domain-fronted mTLS bypass

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.

CriticalCVSS 9.1Not KEV-listedUpdated
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Glexia's TakeAutomated analysiscritical

Security readout for executives and security teams

Plain-English summary

Traefik deployments may expose services intended to require client certificates. A remote, unauthenticated attacker could reach a wildcard-protected backend by using a permissive TLS identity served through the same entrypoint. Successful bypass could compromise sensitive data or permit unauthorized changes.

Executive priority

Treat as an immediate remediation priority where Traefik protects sensitive services with wildcard-based mutual TLS. Upgrade exposed systems first, then validate configuration and certificate enforcement. Deployments lacking the required configuration combination are lower priority but should still be inventoried.

Technical view

In Traefik 3.7.0 through 3.7.2, SNICheck uses exact lookups when resolving TLSOptions for the HTTP Host header, ignoring wildcard mappings. A permissive SNI on the same entrypoint can therefore complete TLS before a wildcard Host routes traffic to a backend configured for mutual TLS.

Likely exposure

Exposure requires Traefik 3.7.0 through 3.7.2, a wildcard host rule with stricter TLSOptions, and another permissive SNI on the same entrypoint. Regular HTTPS and HTTP/2 are affected; HTTP/3 is not required.

Exploitation context

The weakness is remotely reachable, requires no authentication or user interaction, and has low stated complexity. The supplied sources do not report active exploitation, and the CVE is not identified as being in KEV.

Researcher notes

The authorization boundary fails because wildcard TLSOptions are omitted from Host-to-SNI policy comparison. Impact is confidentiality and integrity rather than availability, matching CVSS 3.1 score 9.1. Evidence supports affected versions and configuration prerequisites, but not exploitation in the wild.

Mitigation direction

  • Upgrade affected Traefik installations to version 3.7.3 or later.
  • Prioritize internet-facing entrypoints that combine wildcard mTLS routes with permissive TLS configurations.
  • Review the Traefik advisory and release notes for vendor-supported deployment guidance.
  • Apply relevant Red Hat security updates where Traefik is supplied through affected Red Hat products.

Validation and detection

  • Inventory Traefik versions and confirm no deployment remains on 3.7.0 through 3.7.2.
  • Identify wildcard host rules whose TLSOptions require and verify client certificates.
  • Check whether those entrypoints also serve any SNI using permissive TLS options.
  • After upgrading, verify wildcard-protected routes consistently reject clients without valid certificates.
Prepared
Confidence
high
Sources
5

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cwe · low confidence lookup

CWE-288: Exact CWE lookup

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

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cwe · low confidence lookup

CWE-807: Exact CWE lookup

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

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cve · low confidence lookup

CVE-2026-48491 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

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Vulnerability profileCVE Program record
Severity
Critical
CVSS
9.1 (3.1)
Known Exploited
No
Published

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

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

2CVSS vectors
5Timeline events
2ADP providers
7Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: yesTechnical Impact: total

CVSS vector scores

2 official scores

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
9.1CVSS 3.1CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N3.95.2redhat-SADP
7.8CVSS 4.0HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/SA:N——GitHub_M

Vulnerability scoring details

Base CVSS 4.0 score

7.8High
CVSS 4.0 vector shape for CVE-2026-48491Attack VectorAttack ComplexityAttack RequirementsPrivileges RequiredUser InteractionVS ConfidentialityVS IntegrityVS AvailabilitySS ConfidentialitySS IntegritySS Availability

Vector: 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

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Attack Requirements
NonePresent
Privileges Required
NoneLowHigh
User Interaction
NonePassiveActive
VS Confidentiality
HighLowNone
VS Integrity
HighLowNone
VS Availability
HighLowNone
SS Confidentiality
HighLowNone
SS Integrity
HighLowNone
SS Availability
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. ADP timelineredhat-SADP

    Made public.

  3. CVE publishedCVE Program

    The CVE record was published.

  4. ADP timelineredhat-SADP

    Reported to Red Hat.

  5. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CISA-ADPCISA ADP Vulnrichment
other:ssvc
redhat-SADPTraefik: Traefik: Unauthorized access due to mutual TLS bypass
other:Red Hat severity ratingcvssV3_1
  • 2026-06-23T20:01:26.461Z: Reported to Red Hat.
  • 2026-06-23T19:12:10.819Z: Made public.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
traefiktraefik>= 3.7.0, < 3.7.3Listed
Weakness

CWE details

CWE-288CWE-807

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.

CWE-288 · source CWE mapping

Authentication Bypass Using an Alternate Path or Channel

Authentication Bypass Using an Alternate Path or Channel represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs
CWE-807 · source CWE mapping

Reliance on Untrusted Inputs in a Security Decision

Reliance on Untrusted Inputs in a Security Decision represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs