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Full vulnerability report · 2026
CVE-2026-48491High confidence

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

traefik · traefik

7.8HighCVSS 4.0
Recommended action
Within 7 days

High technical severity with public exploit material referenced by a structured source; prioritise exposed affected systems while verifying vendor guidance.

Patch available
Direct vendor intelligence

Authoritative vendor CSAF and VEX advisories

Structured product status and remediation from the issuing vendor. Product-state explanations are always visible; large lists can be searched or downloaded.

1 current
CVE-2026-48491 · CSAF 2.0 · revision 3 · finalRed Hat Product SecurityTraefik: Traefik: Unauthorized access due to mutual TLS bypass
4 fixed

The vendor explicitly identifies these products or versions as containing the fix.

  • registry.redhat.io/devspaces/traefik-rhel9@sha256:38a0acf8e97a7d0c6a4c8d6815321e35df6ad35736a7338267ce9b5adb118662_amd64 as a component of Red Hat OpenShift Dev Spaces 3.30
  • registry.redhat.io/devspaces/traefik-rhel9@sha256:8b8f3387a3764beb3d8ad6a027b05f42619ccf33165e733e8dc7b3f135895dc5_ppc64le as a component of Red Hat OpenShift Dev Spaces 3.30
  • registry.redhat.io/devspaces/traefik-rhel9@sha256:b338c1060dd859a8747e0812e176ab266d338aea799becd41e48afc50061fb82_s390x as a component of Red Hat OpenShift Dev Spaces 3.30
  • registry.redhat.io/devspaces/traefik-rhel9@sha256:ba0aebd6b6b6ceb676b6990d5bd9f3b7efe40cedd9407149da92c55435ef7db6_arm64 as a component of Red Hat OpenShift Dev Spaces 3.30
Summary
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.
Remediation
Before applying this update, make sure all previously released errata relevant to your system have been applied. For details on how to apply this update, refer to: https://access.redhat.com/articles/11258
Optional official sources

National CERT insights
?CERT means Computer Emergency Response Team; CSIRT is the closely related term Computer Security Incident Response Team.

Select the national-authority views to include. The exact source language is shown on each matched advisory. Your choice is remembered on this device and encoded in the shareable URL.

Official European source

ENISA European Vulnerability Database

Official EUVD identifiers, advisory evidence and known-exploited context. Missing fields are not treated as evidence of low risk.

1 current
ENISA EUVD identifier

EUVD-2026-38575

No EUVD known-exploited evidence

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.

EUVD state
Present in the current official mapping
Known exploitation
Not present in the current ENISA EUVD known-exploited dataset. This is not proof of no exploitation.
ENISA score
7.8 · CVSS 4.0
Advisory evidence
No linked advisory details stored yet
Recommended actionWithin 7 days

High technical severity with public exploit material referenced by a structured source; prioritise exposed affected systems while verifying vendor guidance.

Patch available
01

What, why and how

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.

What

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.

Why

The product requires authentication, but the product has an alternate path or channel that does not require authentication.

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.

What

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.

Why

The product requires authentication, but the product has an alternate path or channel that does not require authentication.

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.

02

Exploit reality and attack path

CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.

Observed exploitation
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
No confirmed evidence

No CISA KEV match was present at the last successful refresh. This means no confirmation from that source, not proof of no exploitation.

Public PoC / exploit material
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
Reference recorded

A structured CVE source labels at least one public reference as exploit material. BlackTree has not independently validated that it is safe, reliable or weaponised.

Likely attack path
a network path → Authentication Bypass Using an Alternate Path or Channel → cause the confidentiality, integrity or availability impact described by the vendor
Attack surface
Network
Privileges required
None: unauthenticated exploitation is possible
User interaction
None
Attack complexity
Low: no specialised conditions are recorded
Security boundary
Not a CVSS 4.0 base metric
Weakness
?CWE means Common Weakness Enumeration: a standard category for the underlying weakness.
CWE-288 ↗

CWE-288: Authentication Bypass Using an Alternate Path or Channel. The product requires authentication, but the product has an alternate path or channel that does not require authentication.

CVSS vector
?CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity.
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

Common Vulnerability Scoring System 4.0: the compact vector below is decoded into plain language.

AVNetworkAttack vector: The vulnerable component can be reached over a network.ACLowAttack complexity: No specialised conditions are required beyond attacker-controlled input.ATNoneAttack requirements: No additional deployment or execution condition is required.PRNonePrivileges required: The attacker does not need an account or existing privileges.UINoneUser interaction: No action by another user is required.VCNoneVulnerable-system confidentiality: No direct loss is represented by this metric.VINoneVulnerable-system integrity: No direct loss is represented by this metric.VANoneVulnerable-system availability: No direct loss is represented by this metric.SCHighSubsequent-system confidentiality: A successful attack can cause a major loss.SIHighSubsequent-system integrity: A successful attack can cause a major loss.SANoneSubsequent-system availability: No direct loss is represented by this metric.
Post-exploitation / living off the land
No specific living-off-the-land technique is confirmed in the structured sources. Monitor normal administration tools for activity inconsistent with the affected service's baseline.
NetworkUnauthenticatedCWE-288Public exploit reference
A

Official authority intelligence

Only matched European and national findings are included. Language selectors and unavailable sources are omitted.

ENISA EUVD · EUVD-2026-38575Official EUVD mapping

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.

Official EUVD record ↗
Cyber Security Agency of Singapore · English · CSA-SB-20260624Security Bulletin 24 June 2026

The Cyber Security Agency of Singapore included this CVE in its official Security Bulletin 24 June 2026, published on 24 June 2026. Open the linked bulletin for the product, severity and reference information published in that issue.

Official advisory ↗
CERT-FR · French · CERTFR-2026-AVI-0690Multiples vulnérabilités dans Traefik

De multiples vulnérabilités ont été découvertes dans Traefik. Elles permettent à un attaquant de provoquer un contournement de la politique de sécurité.

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2026-021317traefikにおける代替パスまたはチャネルを使用した認証回避に関する脆弱性

TraefikはHTTPリバースプロキシおよびロードバランサーです。バージョン3.7.0から3.7.3までの間に、Traefikのドメインフロント保護機能（SNICheck）に重大度の高い脆弱性が存在しました。この脆弱性により、認証されていないクライアントがワイルドカードルータTLSOptionsを介して強制される相互TLSをバイパスできます。ルータがHost(*.example.com)のようなワイルドカードホストルールと、より厳しいTLSオプション（例えばRequireAndVerifyClientCert）を使用している場合、SNICheckはHTTP HostヘッダーのTLSオプションを正確なマップルックアップのみで解決し、ワイルドカードマッチングを適用しません。同じエントリポイントで別の許容的なSNIが提供されている場合、攻撃者は許容的なオプションの下でTLSハンドシェイクを完了し、その後ワイルドカード保護されたバックエンドを対象とするHTTP Hostヘッダーを送信することで、クライアント証明書を提示せずにアクセスできるようになります。これは通常のHTTPS / HTTP-2パスに影響し、HTTP/3は必要ありません。この脆弱性はバージョン3.7.3で修正されました。

Official advisory ↗
03

Patch and workaround

Operational remediation based on structured source evidence.

Status
?Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change.
Patch available
Affected
traefik: >= 3.7.0, < 3.7.3
Fixed
Action
Before applying this update, make sure all previously released errata relevant to your system have been applied. For details on how to apply this update, refer to: https://access.redhat.com/articles/11258
Workaround
No verified workaround is recorded. If business-safe, reduce exposure to the affected interface and allow only trusted sources until authoritative guidance is available.
04

Evidence and provenance

Published 23 Jun 2026 · Last source change 2 Sept 2026, 12:04 UTC · CWE-288 · Authentication Bypass Using an Alternate Path or Channel

CVE recordCVE.org · 5.2
CVSS sourceCNA
EPSS source
?The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.
FIRST · tracked since 2026-08-14
European sourceENISA EUVD · EUVD-2026-38575
Product sourceCNA
Remediation sourceVendor CSAF · Red Hat Product Security
CWE sourceCNA
NVD statusNVD modified after enrichment

Core structured fields are present and their contributing authorities are shown above.

Material change intelligence

What changed after publication

View recent updates ↗
  1. Vendor guidanceAuthoritative vendor guidance changed from authoritative remediation link · patch, vendor advisory to authoritative remediation link · patch.
    Before
    authoritative remediation link · patch, vendor advisory
    After
    authoritative remediation link · patch
    security-advisories@github.com ↗
  2. Vendor guidanceAuthoritative vendor guidance changed from authoritative remediation link · patch to authoritative remediation link · patch, vendor advisory.
    Before
    authoritative remediation link · patch
    After
    authoritative remediation link · patch, vendor advisory
    security-advisories@github.com ↗
Material fields only · duplicate refreshes suppressed · history retained for the configured operational retention period
CVE published
Fixed release or patch reference recorded
ENISA EUVD · EUVD-2026-38575↗Vendor CSAF · Red Hat Product Security↗Public exploit reference↗Patch or update reference↗Official CVE record (CNA and ADP data)↗NVD record↗
Technical terms and abbreviations used in this report
CVE
Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
CVSS
Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
EPSS
Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
CWE
Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
CNA
CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
CISA ADP
Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
NVD
National Vulnerability Database: NIST's enrichment service for CVE records.
CERT / CSIRT
A computer security incident response team that publishes warnings or coordinates incident response.
PoC
Proof of concept: public material that demonstrates or helps reproduce exploitation.
CSAF
Common Security Advisory Framework: a machine-readable format for security advisories.
LoTL
Living off the land: abuse of legitimate tools or system functions during an attack.
Free version - for non-commercial use only.CVE-2026-48491 · cve.blacktree.nl