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CVE-2026-41920 – Improper Access Control (SNI/Host Header Policy Bypass) – Apache Traffic Server …

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Summary

CVE-2026-41920 is a critical Improper Access Control vulnerability (CWE-284) in Apache Traffic Server, caused by the failure to properly enforce SNI (Server Name Indication) to Host header matching policies. It affects all deployments running versions 9.0.0 through 9.1.14 and 10.0.0 through 10.1.3, and carries a CVSS v3.1 score of 9.3 (Critical). The flaw requires no authentication and no user interaction, and is exploitable over the network from any remote attacker.

Technical details

  • Root cause: Apache Traffic Server does not correctly enforce its configured policy requiring the TLS SNI hostname to match the HTTP Host header. When this policy is bypassed, traffic routing and access control decisions based on the expected SNI/Host correlation can be subverted.
  • Trigger conditions: The vulnerability is exploitable remotely over the network with low attack complexity, no required privileges, and no user interaction — CVSS vector AV:N/AC:L/PR:N/UI:N.
  • Attack vector: An unauthenticated remote attacker can present a mismatched SNI and Host header in a crafted HTTPS request to circumvent the access control policy governing which virtual hosts or backend resources are accessible.
  • Impact: The CVSS v3.1 vector includes S:C (Scope Changed) and I:H (High Integrity impact), indicating that successful exploitation can affect components beyond the vulnerable Traffic Server instance itself — consistent with unauthorized access to backend systems or virtual hosts that the policy was intended to protect. A low confidentiality impact (C:L) is also scored, indicating potential for limited information disclosure.

Affected software

  • Apache Traffic Server 9.0.0 through 9.1.14
  • Apache Traffic Server 10.0.0 through 10.1.3

Severity

CVSS v3.1 Base Score: 9.3 (Critical)
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:H/A:N

Mitigation and recommended actions

  • Immediate action: Upgrade to Apache Traffic Server 9.1.15 or 10.1.4, which contain the vendor-provided fix for this issue.
  • If immediate patching is not feasible, restrict network-level access to Apache Traffic Server instances from untrusted sources using firewall rules or upstream access controls, and review SNI/Host matching policy configurations.

IONIX Status

The IONIX research team is tracking ongoing exploitation attempts and recommends immediate patching. Potentially affected assets are outlined in this post.

References

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