CVE-2016-5396 in Traffic Server
Summary
by MITRE
Apache Traffic Server 6.0.0 to 6.2.0 are affected by an HPACK Bomb Attack.
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Analysis
by VulDB Data Team • 11/29/2022
The Apache Traffic Server vulnerability CVE-2016-5396 represents a critical security flaw that affects versions 6.0.0 through 6.2.0, specifically exposing the system to HPACK bomb attacks. This vulnerability resides within the HTTP/2 implementation of the traffic server, where the HPACK compression algorithm is utilized to efficiently encode HTTP headers. The flaw allows malicious actors to exploit the compression mechanism through carefully crafted header sequences that cause excessive memory consumption and processing overhead. The vulnerability stems from inadequate input validation and resource management within the HPACK decoder, which fails to properly limit the expansion ratio of compressed header data during decompression processes.
The technical exploitation of this vulnerability occurs when an attacker sends specially crafted HTTP/2 requests containing maliciously constructed header fields that trigger exponential memory growth during HPACK decompression. The HPACK algorithm itself is designed to compress headers efficiently by maintaining a dynamic table of previously seen header fields, but the implementation in Apache Traffic Server lacks proper bounds checking on the decompression process. This allows attackers to construct header sequences that cause the server to allocate excessive memory resources while processing what appears to be legitimate traffic. The vulnerability is categorized under CWE-400 as an unspecified vulnerability in resource management, specifically related to memory consumption issues during data decompression.
Operationally, this vulnerability can lead to significant service disruption and potential denial of service conditions within the Apache Traffic Server environment. When exploited, the HPACK bomb attack can cause the server to consume all available memory resources, leading to system crashes, process terminations, and complete service unavailability. The impact extends beyond simple denial of service as the resource exhaustion can affect other services running on the same system and potentially cause cascading failures. Attackers can leverage this vulnerability to perform sustained attacks against web applications that rely on Apache Traffic Server for content delivery, making it particularly dangerous in high-traffic environments where the server handles thousands of concurrent connections.
The mitigation strategies for CVE-2016-5396 primarily involve upgrading to Apache Traffic Server versions 6.2.1 or later, where the HPACK implementation has been patched to include proper bounds checking and memory limits. Organizations should also implement network-level protections such as rate limiting and connection throttling to prevent exploitation attempts. Additionally, monitoring systems should be configured to detect unusual memory consumption patterns and excessive header processing that may indicate an active attack. Security teams should consider implementing HTTP/2 specific security controls and regularly review their traffic server configurations to ensure proper resource limits are in place. This vulnerability aligns with ATT&CK technique T1499.004 for resource exhaustion and represents a critical weakness in the HTTP/2 protocol implementation that requires immediate attention and remediation to prevent potential system compromise and service disruption.