CVE-2016-10711 in Pound
Summary
by MITRE
Apsis Pound before 2.8a allows request smuggling via crafted headers, a different vulnerability than CVE-2005-3751.
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Analysis
by VulDB Data Team • 02/03/2023
The vulnerability identified as CVE-2016-10711 affects Apsis Pound versions prior to 2.8a and represents a significant HTTP request smuggling flaw that exploits crafted header manipulation. This vulnerability operates through the manipulation of HTTP headers in a manner distinct from the well-known CVE-2005-3751, which specifically addressed HTTP request smuggling through the use of the Transfer-Encoding header. The Apsis Pound proxy server, designed to handle and route HTTP requests, becomes susceptible to this attack when processing specially crafted HTTP headers that can cause the proxy to misinterpret the boundaries of HTTP requests and responses. The flaw stems from inadequate validation and processing of HTTP headers that should normally be handled consistently by web servers and proxies, creating a potential attack vector where malicious actors can manipulate the proxy behavior to inject or redirect requests.
The technical implementation of this vulnerability involves the manipulation of HTTP headers such as Content-Length, Transfer-Encoding, and other header fields that define how HTTP messages should be processed. When Apsis Pound processes requests with crafted headers, it fails to properly validate or normalize these header values, allowing an attacker to construct HTTP requests that appear valid to the client but are interpreted differently by the proxy server. This discrepancy creates opportunities for request smuggling where an attacker can send multiple requests within a single HTTP connection or manipulate how requests are forwarded to backend servers. The vulnerability specifically targets the proxy's header parsing logic and connection handling mechanisms, exploiting the fact that different systems may interpret identical header values differently, particularly when dealing with chunked transfer encoding or content length inconsistencies.
The operational impact of CVE-2016-10711 extends beyond simple request manipulation and can enable several sophisticated attack scenarios including cache poisoning, session hijacking, and cross-site scripting attacks. An attacker leveraging this vulnerability can potentially bypass security controls implemented at the proxy level, gain unauthorized access to backend systems, or manipulate how requests are processed and routed within the network infrastructure. The vulnerability affects organizations that rely on Apsis Pound as a reverse proxy or load balancer, particularly those with complex web application architectures where proper header handling is crucial for maintaining security boundaries. The attack surface is particularly concerning in environments where the proxy server acts as a gateway between internal and external networks, as it could allow attackers to access internal resources that would otherwise be protected by network segmentation.
Organizations should immediately upgrade to Apsis Pound version 2.8a or later to remediate this vulnerability, as the patch addresses the core header parsing logic that enables the request smuggling attack. Additionally, implementing proper HTTP header validation and normalization at the proxy level can provide defense-in-depth measures against similar vulnerabilities. Network monitoring should be enhanced to detect unusual header patterns or request behaviors that might indicate exploitation attempts. The vulnerability aligns with CWE-444, which covers HTTP request smuggling, and maps to ATT&CK technique T1190, specifically targeting the exploitation of proxy servers and web application firewalls through header manipulation. Security teams should also consider implementing web application firewalls that can detect and block suspicious header combinations, as well as conducting regular security assessments of proxy configurations to identify potential header-related vulnerabilities that could be exploited in similar fashion.