CVE-2005-3751 in Pound
Summary
by MITRE
HTTP request smuggling vulnerability in Pound before 1.9.4 allows remote attackers to poison web caches, bypass web application firewall protection, and conduct XSS attacks via an HTTP request with conflicting Content-length and Transfer-encoding headers.
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Analysis
by VulDB Data Team • 06/20/2019
The CVE-2005-3751 vulnerability represents a critical HTTP request smuggling flaw in the Pound load balancer software prior to version 1.9.4. This vulnerability arises from the software's improper handling of conflicting HTTP headers, specifically when both Content-Length and Transfer-Encoding headers are present in a single HTTP request. The flaw enables malicious actors to manipulate how the server processes incoming requests, creating opportunities for various attack vectors that compromise web security infrastructure. The vulnerability is particularly dangerous because it affects the fundamental HTTP request processing mechanism that underlies web communication and security controls.
The technical implementation of this vulnerability stems from Pound's inadequate validation and processing of HTTP headers during request parsing. When an attacker crafts an HTTP request containing both Content-Length and Transfer-Encoding headers with conflicting values, the load balancer fails to properly normalize or reject the request according to HTTP specifications. This creates a parsing ambiguity that can be exploited to inject malicious requests into web caches or bypass security controls. The specific flaw aligns with CWE-16, which addresses configuration issues in software that can lead to security vulnerabilities, and CWE-444, which covers HTTP request smuggling vulnerabilities that arise from improper HTTP message parsing. The vulnerability demonstrates how a seemingly simple header conflict can create complex security implications when the HTTP processing logic does not properly handle edge cases.
The operational impact of CVE-2005-3751 extends far beyond simple request processing failures, as it enables sophisticated attack scenarios that can compromise entire web infrastructures. Attackers can exploit this vulnerability to poison web caches by injecting malicious content that gets stored in cache servers, potentially serving compromised content to multiple users. The vulnerability also allows bypass of web application firewalls that rely on proper HTTP request parsing for security enforcement, effectively rendering security controls ineffective. Additionally, the flaw creates opportunities for cross-site scripting attacks where attackers can inject malicious scripts into web applications through the manipulated request flow. This vulnerability directly maps to ATT&CK technique T1190, which covers exploitation of vulnerabilities in web applications and infrastructure components, and T1566, which involves the manipulation of web traffic to bypass security controls.
Mitigation strategies for CVE-2005-3751 require immediate implementation of software updates to Pound version 1.9.4 or later, which includes proper header validation and conflict resolution mechanisms. Organizations should also implement comprehensive HTTP header validation policies at multiple network layers, including load balancers, firewalls, and web application firewalls, to detect and block malformed requests containing conflicting headers. Network administrators should deploy intrusion detection systems with signature-based detection for known patterns of this attack, and implement request normalization rules that ensure consistent header processing. Security teams should conduct thorough vulnerability assessments of all HTTP processing components in their infrastructure to identify similar vulnerabilities that may exist in other software components, particularly those handling HTTP communication. Additionally, organizations should implement proper logging and monitoring of HTTP request processing to detect anomalous behavior that may indicate exploitation attempts, and establish incident response procedures specifically addressing HTTP request smuggling vulnerabilities.