CVE-2026-111804 in Traffic Server
Summary
by MITRE • 10/22/2026
Apache Traffic Server's experimental wasm plugin has a use-after-free in its transaction-close handler and forwards unvalidated guest-supplied metric IDs to the internal stats API.
This issue affects Apache Traffic Server: from 10.0.0 through 10.1.4, 10.2.0.
Users are recommended to upgrade to version 10.1.5 or 10.2.1, which fix the issue.
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Analysis
by VulDB Data Team • 10/22/2026
The vulnerability identified in Apache Traffic Server involves a critical memory safety flaw within its experimental WebAssembly plugin subsystem, specifically located in the transaction-close handler. This component is responsible for managing the lifecycle of transactions processed by the reverse proxy and caching server. When a client connection or request transaction concludes, the system invokes cleanup routines to release resources associated with that session. In versions 10.0.0 through 10.2.0, this process contains a use-after-free error, meaning the software attempts to access memory that has already been deallocated and potentially reused for other purposes. This type of flaw typically arises from incorrect pointer management or race conditions where the lifetime of an object is not properly synchronized with its usage in concurrent execution contexts.
Compounding the severity of this memory corruption issue is a lack of input validation regarding metric identifiers supplied by guest code running within the WebAssembly sandbox. The plugin forwards these unvalidated IDs directly to the internal statistics API without performing sufficient boundary checks or type verification. This design oversight allows an attacker who can influence the execution flow of the WebAssembly module, potentially through crafted HTTP requests that trigger specific transaction paths, to manipulate how memory is accessed during the cleanup phase. By controlling the metric ID passed to the stats system, an adversary may be able to target specific memory addresses or corrupt internal data structures associated with traffic metrics and logging systems.
The operational impact of this vulnerability extends beyond simple denial of service scenarios involving crashes. While a successful exploitation could lead to server instability by causing segmentation faults or application termination, use-after-free vulnerabilities are particularly dangerous because they can often be leveraged for arbitrary code execution. An attacker might exploit the memory corruption to overwrite function pointers or object vtables within the process space of Apache Traffic Server. Given that this software typically runs with elevated privileges to handle network traffic and cache data, achieving remote code execution could allow an adversary to gain full control over the underlying host system, pivot into internal networks, or exfiltrate sensitive cached content.
This flaw aligns closely with Common Weakness Enumeration CWE-416, which describes use-after-free conditions where a pointer is used after it has been freed, leading to undefined behavior and potential security breaches. Furthermore, the aspect of forwarding unvalidated inputs from a guest environment relates to CWE-20, Improper Input Validation, as the system fails to verify that the metric IDs conform to expected formats or ranges before processing them in critical internal APIs. From an offensive perspective, this vulnerability could be categorized under MITRE ATT&CK techniques involving exploitation for privilege escalation or initial access if the server is exposed to untrusted networks and the WebAssembly plugin is enabled with permissive execution policies.
To mitigate these risks, organizations running Apache Traffic Server must prioritize immediate patching by upgrading to version 10.1.5 or 10.2.1, where the memory management logic in the transaction-close handler has been corrected and input validation for guest-supplied metrics has been implemented. For environments that cannot immediately upgrade, it is advisable to disable the experimental WebAssembly plugin if it is not strictly required for business operations, thereby removing the attack surface entirely. Additionally, deploying web application firewalls or network intrusion detection systems may help identify anomalous traffic patterns attempting to exploit transaction handling anomalies, although such controls are secondary to applying the vendor-provided security patches. Regular auditing of third-party plugins and strict adherence to least-privilege principles for service accounts running Traffic Server further reduce the potential blast radius should a vulnerability be exploited in other components.