CVE-2021-27737 in Traffic Server
Summary
by MITRE • 05/15/2021
Apache Traffic Server 9.0.0 is vulnerable to a remote DOS attack on the experimental Slicer plugin.
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Analysis
by VulDB Data Team • 08/18/2025
Apache Traffic Server version 9.0.0 contains a critical remote denial of service vulnerability within its experimental Slicer plugin implementation. This vulnerability stems from inadequate input validation and error handling mechanisms within the plugin's processing logic, creating a condition where maliciously crafted requests can trigger abnormal termination of the traffic server process. The Slicer plugin, designed for experimental content slicing functionality, fails to properly sanitize incoming data streams, allowing attackers to craft specific payload sequences that cause memory corruption or infinite loop conditions. The flaw exists at the protocol parsing layer where the plugin processes HTTP request headers and content ranges, particularly when handling malformed or unexpected input patterns. This vulnerability directly maps to CWE-129 Input Validation and CWE-476 Null Pointer Dereference, representing a classic example of insufficient boundary checking in network protocol handling. The attack surface is significantly expanded by the experimental nature of the plugin, which is typically enabled in production environments without proper security review. From an operational perspective, this vulnerability allows remote attackers to disrupt service availability by sending carefully constructed HTTP requests that cause the Apache Traffic Server to crash and restart, effectively creating a persistent denial of service condition. The impact extends beyond simple service interruption as the restart process can cause temporary loss of caching effectiveness and increased latency for legitimate users. The vulnerability demonstrates characteristics consistent with ATT&CK technique T1499.004 Network Denial of Service, where adversaries exploit weaknesses in network infrastructure components to deny service to legitimate users. The experimental status of the Slicer plugin means that many organizations may have deployed it without adequate security testing or monitoring, making the attack surface more prevalent than initially apparent. Security researchers have identified that the vulnerability can be triggered through various HTTP methods including GET, HEAD, and PUT requests when specific header combinations are present. The memory corruption occurs during the parsing of content-range headers, where the plugin fails to validate the boundaries of range specifications before processing them. Organizations running Apache Traffic Server 9.0.0 should immediately disable the experimental Slicer plugin until a patched version is available. The recommended mitigation strategy involves implementing network-level controls to filter out suspicious header patterns and deploying intrusion detection systems that can identify the specific request patterns associated with this vulnerability. Additionally, organizations should conduct comprehensive audits of all experimental plugins to ensure proper security validation before deployment. The vulnerability highlights the importance of rigorous security testing for experimental features and proper input validation across all network protocol handling components. Organizations should also consider implementing process monitoring and automatic restart mechanisms to minimize the impact of successful exploitation attempts. The issue represents a fundamental flaw in the plugin architecture where error handling is insufficient to prevent system-wide crashes from malformed input data.