CVE-2024-35296 in Traffic Server
Summary
by MITRE • 07/26/2024
Invalid Accept-Encoding header can cause Apache Traffic Server to fail cache lookup and force forwarding requests.
This issue affects Apache Traffic Server: from 8.0.0 through 8.1.10, from 9.0.0 through 9.2.4.
Users are recommended to upgrade to version 8.1.11 or 9.2.5, which fixes the issue.
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 09/28/2024
The vulnerability described in CVE-2024-35296 represents a critical flaw in Apache Traffic Server's handling of HTTP Accept-Encoding headers that fundamentally undermines the proxy server's caching mechanism. This issue manifests when the server receives malformed or invalid Accept-Encoding headers from client requests, causing the traffic server to bypass its normal cache lookup procedures and instead forward all requests directly to origin servers. The flaw affects multiple versions of the software including the 8.x series from 8.0.0 through 8.1.10 and the 9.x series from 9.0.0 through 9.2.4, indicating a widespread impact across the product's lifecycle. The root cause stems from inadequate input validation within the HTTP header processing pipeline, where the server fails to properly handle malformed Accept-Encoding values that should be gracefully ignored or normalized rather than triggering a complete cache bypass mechanism.
The technical implementation of this vulnerability exploits the HTTP protocol's caching behavior by manipulating the Accept-Encoding header field which is used to indicate the content codings that the client is willing to accept. When the traffic server encounters an invalid Accept-Encoding header, the processing logic incorrectly determines that caching cannot be safely performed, leading to a forced forwarding decision regardless of whether cached content might be available for the requested resource. This behavior creates a denial of service condition where legitimate cached content is bypassed, resulting in unnecessary load on origin servers and increased latency for end users. The flaw operates at the application layer of the OSI model and represents a classic case of improper input validation where malformed HTTP headers trigger unexpected control flow behavior.
The operational impact of this vulnerability extends beyond simple performance degradation to potentially compromise the entire caching infrastructure of systems relying on Apache Traffic Server. When exploited, the vulnerability forces a complete bypass of the cache layer, meaning that every request that triggers the invalid header condition results in a round trip to the origin server instead of utilizing cached content. This can lead to significant resource exhaustion on backend systems, increased network traffic, and degraded user experience through higher latency responses. The vulnerability particularly affects high-traffic environments where caching efficiency is critical for performance optimization, making it especially dangerous for content delivery networks and web applications that depend on traffic server's caching capabilities to handle large volumes of requests. Organizations may experience cascading performance issues as the origin servers become overwhelmed with redundant requests that could have been satisfied from cache.
Security implications of this vulnerability align with CWE-20, which describes improper input validation as a fundamental weakness in software systems. The flaw creates an attack surface where malicious actors can intentionally craft requests with invalid Accept-Encoding headers to force cache bypass and potentially amplify resource consumption on origin servers. This behavior can be leveraged as part of a broader attack strategy to degrade service availability or to increase costs through unnecessary resource consumption. The vulnerability also relates to ATT&CK technique T1499.004 which involves network denial of service through resource exhaustion, as the forced forwarding of requests can overwhelm origin server capacity. Organizations should implement immediate mitigations including upgrading to the patched versions 8.1.11 or 9.2.5 as recommended by the vendor, while also considering implementing request filtering mechanisms to detect and block malformed Accept-Encoding headers as additional defensive measures. The vulnerability demonstrates the critical importance of robust input validation in proxy and caching systems where malformed requests can have cascading effects on entire infrastructure components.