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CVE-2026-40912: Traefik: StripPrefixRegex auth bypass via Path/RawPath desync

Traefik is an HTTP reverse proxy and load balancer. Prior to versions 2.11.43, 3.6.14, and 3.7.0-rc.2, there is a high severity authentication bypass vulnerability in Traefik's StripPrefixRegex middleware when used in combination with ForwardAuth, BasicAuth, or DigestAuth. The middleware matches the regex against the decoded URL path but uses the resulting byte length to slice the percent-encoded raw path. When a dot (or multiple dots) appears in the prefix portion of the URL, the raw path after stripping becomes a dot-segment (e.g. /./admin/secret). ForwardAuth receives this dot-segment path in X-Forwarded-Uri, which does not match the protected path patterns and therefore allows the request through. The backend then normalizes the dot-segment to the real path per RFC 3986 and serves the protected content An unauthenticated attacker can exploit this against any backend that performs dot-segment normalization. This issue has been patched in versions 2.11.43, 3.6.14, and 3.7.0-rc.2.

HighCVSS 8.6Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

CVE-2026-40912 lets unauthenticated users bypass authentication in some Traefik deployments. The risk exists when StripPrefixRegex is combined with ForwardAuth, BasicAuth, or DigestAuth. A crafted URL path can make the auth layer evaluate a different path than the backend ultimately serves, exposing protected content.

Executive priority

Prioritize remediation for internet-facing Traefik instances protecting sensitive admin, API, or customer data paths. This is high urgency where the affected middleware chain is present because exploitation requires no credentials and can expose protected content. Environments without the specific middleware combination should still verify configuration.

Technical view

Traefik decodes the URL path for StripPrefixRegex matching but slices the percent-encoded RawPath using the decoded byte length. Dot characters in the stripped prefix can leave a dot-segment path forwarded for auth checks. Auth middleware may miss protected path rules, while a backend normalizes the path and serves the protected resource.

Likely exposure

Exposure is limited to Traefik versions before 2.11.43, 3.6.14, or 3.7.0-rc.2 where StripPrefixRegex is used with ForwardAuth, BasicAuth, or DigestAuth. Backends that normalize dot-segments are specifically relevant. Deployments without this middleware combination are not described as affected by the source bundle.

Exploitation context

The CVSS score is 8.6 with network access, low complexity, no privileges, and no user interaction. The bundle marks KEV as false, and no provided source states active exploitation. The described impact is confidentiality loss through authentication bypass, not integrity or availability loss.

Researcher notes

The key condition is a Path/RawPath desynchronization in StripPrefixRegex feeding an authentication decision that sees a dot-segment path, followed by backend normalization. The source bundle provides affected version ranges and patched versions, but no evidence of KEV listing or confirmed exploitation.

Mitigation direction

  • Upgrade Traefik 2.x deployments to 2.11.43 or later.
  • Upgrade Traefik 3.0-3.6 deployments to 3.6.14 or later.
  • Move 3.7 prerelease deployments to 3.7.0-rc.2 or later.
  • Review routes using StripPrefixRegex with ForwardAuth, BasicAuth, or DigestAuth.
  • Check Traefik and Red Hat guidance for product-specific remediation details.

Validation and detection

  • Inventory Traefik versions across edge, ingress, and service proxy deployments.
  • Inspect dynamic configuration for StripPrefixRegex paired with affected authentication middleware.
  • Confirm protected routes still require authentication after upgrading or changing middleware.
  • Review access logs for unusual encoded path and dot-segment requests.
  • Track Red Hat status if using packaged or downstream Traefik builds.
Prepared
Confidence
high
Sources
10

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

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ATT&CK lookup starting points

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cwe · medium confidence lookup

CWE-22: File access and web shell behavior lookup

File traversal and upload weaknesses can lead teams to review file, web shell, execution, and collection telemetry. 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-706: Exact CWE lookup

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description · low confidence lookup

Credential and access behavior lookup

The CVE wording references authentication or credential exposure, so valid-account and credential-access review may help. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.

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cve · low confidence lookup

CVE-2026-40912 mapping review

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Vulnerability profileCVE Program record
Severity
High
CVSS
8.6 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/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
9Source links

SSVC decision data

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

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
8.6CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N3.94redhat-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:L/SA:N——GitHub_M

Vulnerability scoring details

Base CVSS 4.0 score

7.8High
CVSS 4.0 vector shape for CVE-2026-40912Attack 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:L/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-SADPgithub.com/traefik/traefik: Traefik: Authentication bypass via crafted URL dot-segments in StripPrefixRegex middleware
other:Red Hat severity ratingcvssV3_1
  • 2026-04-30T21:01:06.544Z: Reported to Red Hat.
  • 2026-04-30T20:38:21.969Z: Made public.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
traefiktraefik< 2.11.43, >= 3.0.0-beta1, < 3.6.14, >= 3.7.0-ea.1, < 3.7.0-rc.2Listed
Weakness

CWE details

CWE-22CWE-706

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

CWE-22 · source CWE mapping

Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')

Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal') represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs
CWE-706 · source CWE mapping

Use of Incorrectly-Resolved Name or Reference

Use of Incorrectly-Resolved Name or Reference represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

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