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CVE-2026-58155 – HTTP Request Smuggling / Policy Bypass – Apache Traffic Server 8.0.0–10.1.3

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Summary

CVE-2026-58155 is a critical HTTP request smuggling and security policy bypass vulnerability in Apache Traffic Server (ATS), a widely-deployed open-source reverse proxy and caching server. The flaw stems from ATS truncating over-long HTTP header names, producing header aliasing that causes inconsistent request interpretation between ATS and downstream systems (CWE-444). With a CVSS v3.1 score of 9.3 (Critical) and no authentication or user interaction required, any remote attacker can exploit this flaw against any affected internet-facing ATS instance.

Technical details

  • Root cause: Apache Traffic Server truncates HTTP header names that exceed an internal length limit. This produces "header aliasing" — a truncated header name may collide with a different, legitimate header name, causing ATS and backend servers to interpret the same request differently (CWE-444: Inconsistent Interpretation of HTTP Requests).
  • Trigger conditions: An attacker crafts an HTTP request containing an over-length header name. No authentication, special privileges, or victim interaction is required. Attack complexity is low.
  • Attack vector: Network-reachable; exploitable directly against any internet-exposed ATS instance over HTTP or HTTPS.
  • Impact: The inconsistent header interpretation enables HTTP request smuggling and security policy bypass at the proxy layer. The CVSS Scope is Changed, meaning impact extends beyond ATS itself — downstream backend systems are affected. The integrity impact is rated High (I:H), with a Low confidentiality impact (C:L). Practical consequences include bypassing ATS-enforced access controls, cache poisoning, request hijacking to backend services, and potential unauthorized access to internal resources.

Affected software

  • Apache Traffic Server 8.0.0 through 8.1.9
  • Apache Traffic Server 9.0.0 through 9.2.14
  • 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 – patch: Upgrade to Apache Traffic Server 9.2.15 or 10.1.4, which contain the vendor-provided fix. ATS 8.x does not have a patched release; users on the 8.x branch should migrate to a supported version.
  • If immediate patching is not possible: Restrict network access to ATS instances to only trusted upstream clients, and review any security policies enforced at the ATS proxy layer that could be bypassed via request smuggling.

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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