CVE-2026-58178 in Traffic Server
Summary
by MITRE • 07/29/2026
The Apache Traffic Server ESI plugin can recurse without bound and fetch attacker-controlled URLs.
This issue affects Apache Traffic Server: from 8.0.0 through 8.1.9, from 9.0.0 through 9.2.14, from 10.0.0 through 10.1.3.
Users are recommended to upgrade to version 9.2.15 or 10.1.4, which fix the issue.
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Analysis
by VulDB Data Team • 07/29/2026
The Apache Traffic Server ESI plugin vulnerability represents a critical recursive processing flaw that enables unlimited recursion and arbitrary URL fetching capabilities. This vulnerability exists within the Edge Side Includes implementation where the system fails to properly validate or limit the depth of recursive includes, allowing malicious actors to craft specially formatted ESI documents that trigger infinite recursion patterns. The issue manifests when the ESI processor encounters nested include directives that reference each other in a circular manner, causing the system to continuously fetch and process content from attacker-controlled URLs without proper bounds checking.
The technical implementation flaw stems from inadequate recursion depth monitoring within the ESI processing engine, which operates under the assumption that recursive includes will naturally terminate. This design oversight creates a denial of service condition where the server becomes overwhelmed with continuous requests to external resources, consuming significant computational and network resources. The vulnerability affects multiple versions across different release streams, indicating a persistent issue in the core ESI processing logic that spans several major releases. When exploited, the system's recursive behavior can lead to resource exhaustion, making the server unavailable to legitimate users while simultaneously creating potential attack vectors for information disclosure through repeated fetches of sensitive content.
The operational impact of this vulnerability extends beyond simple denial of service scenarios into more complex attack surface considerations. An attacker can leverage this flaw not only to consume server resources but also to potentially access internal network resources that would normally be protected by firewall rules, as the recursive fetching mechanism may bypass normal access controls. The continuous nature of the recursion can cause memory exhaustion, CPU starvation, and network bandwidth saturation, effectively rendering the affected server unusable for legitimate traffic processing. This vulnerability particularly impacts high-traffic environments where the ESI plugin is actively used for dynamic content assembly, as the resource consumption can quickly overwhelm system capabilities.
Security implications align with CWE-674, which addresses "Uncontrolled Recursion" in software systems, and maps to ATT&CK technique T1499.004 for "Endpoint Denial of Service." The vulnerability creates a pathway for attackers to perform resource exhaustion attacks that can be amplified through the recursive processing nature. Organizations should prioritize upgrading to version 9.2.15 or 10.1.4, which implement proper recursion depth limiting and include bounds checking mechanisms. Additional mitigations include implementing ESI content validation policies, restricting external URL access for ESI includes, and monitoring for unusual recursive request patterns in server logs. The fix addresses the root cause by introducing maximum recursion limits and proper termination conditions within the ESI processing pipeline, preventing unbounded execution while maintaining legitimate use cases for dynamic content assembly.