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CVE-2026-58189 – Redirect-Limit Bypass / SSRF Amplification – Apache Traffic Server 8.0.0–10.1.3

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Summary

CVE-2026-58189 is a high-severity Server-Side Request Forgery (SSRF) amplification vulnerability (CWE-918) in Apache Traffic Server (ATS), a widely deployed internet-facing reverse proxy, forward proxy, and CDN caching platform. The flaw allows ATS plugins to reset the redirect retry counter, effectively bypassing the configured redirect limit and enabling unauthenticated network attackers to trigger unlimited outbound requests from the server. It carries a CVSS v3.1 score of 7.5 (High) and affects all supported major branches of Apache Traffic Server.

Technical details

  • Root cause: ATS plugins are able to reset the internal redirect retry counter, circumventing the redirect limit that is intended to cap the number of times ATS will follow HTTP redirects on behalf of a client request. This design flaw is classified under CWE-918 (Server-Side Request Forgery).
  • Trigger conditions: An unauthenticated remote attacker can craft HTTP requests that cause ATS to follow a theoretically unbounded chain of redirects toward arbitrary internal or external destinations, driven by plugin-controlled counter resets.
  • Attack vector: Fully network-accessible (AV:N), no authentication required (PR:N), no user interaction needed (UI:N), and low attack complexity (AC:L).
  • Impact: The primary risk is SSRF amplification — the server is induced into making large volumes of unauthorized outbound HTTP requests. This can be used to probe internal infrastructure, bypass network segmentation, exhaust upstream connection pools, or cause availability degradation (A:H per CVSS scoring).

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: 7.5 (High)
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS v4.0 Base Score: 8.2 (High)

Mitigation and recommended actions

  • Immediate action — upgrade: Apache Software Foundation recommends upgrading to version 9.2.15 or version 10.1.4, which contain the fix for this vulnerability.
  • Version 8.x branch: No fix has been released for the 8.x branch. Users on versions 8.0.0–8.1.9 should migrate to a patched release on the 9.2.x or 10.1.x branch.
  • If immediate patching is not feasible: Consider restricting internet-facing access to ATS instances and applying egress filtering at the network level to limit the range of outbound connections the server can initiate, thereby reducing the SSRF amplification impact.

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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