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CVE-2026-58150 – HTTP/2 Request Smuggling – Apache Traffic Server 8.0.0–10.1.3

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Summary

CVE-2026-58150 is a critical HTTP/2 request smuggling vulnerability in Apache Traffic Server (ATS), rated CVSS 10.0 (Critical). The flaw arises because ATS does not reject Transfer-Encoding headers in HTTP/2 requests — violating the HTTP/2 specification — which enables H2.TE-based downgrade request smuggling attacks against downstream backend servers. The vulnerability is remotely exploitable with no authentication, no user interaction, and low attack complexity, and its scope-changed CVSS rating reflects that exploitation can extend beyond ATS itself to the backend infrastructure it proxies.

Technical details

  • Root cause: ATS fails to enforce the HTTP/2 specification’s prohibition on Transfer-Encoding headers (CWE-444: Inconsistent Interpretation of HTTP Requests). When ATS downgrades an HTTP/2 connection to HTTP/1.1 for backend communication, the improperly forwarded Transfer-Encoding header creates ambiguity in request boundary parsing on the backend.
  • Trigger conditions: An unauthenticated remote attacker sends a crafted HTTP/2 request containing a Transfer-Encoding header to any ATS reverse proxy instance running a vulnerable version.
  • Attack vector: Network-reachable; requires no privileges, no user interaction, and presents low attack complexity — exploitable directly from the internet against any exposed ATS deployment.
  • Impact: Successful exploitation can enable poisoning of shared backend request queues, bypassing of upstream security controls (such as authentication layers or WAFs), cache poisoning, and session hijacking. The CVSS scope change (S:C) reflects that the blast radius extends beyond ATS to downstream backend servers sharing the same connection pool.

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: 10.0 (Critical)
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N

Mitigation and recommended actions

  • Immediate: Upgrade to Apache Traffic Server 9.2.15 or 10.1.4, which contain the vendor-provided fix for this issue, as recommended by the Apache Software Foundation.
  • Users running the 8.x branch (8.0.0–8.1.9) should migrate to a patched 9.2.x or 10.1.x release, as no fix has been issued for the 8.x line.
  • If immediate patching is not feasible, consider restricting internet-facing access to ATS instances and reviewing backend connection configurations to reduce exposure.

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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