CVE-2019-18679 in Web Proxy
Summary
by MITRE
An issue was discovered in Squid 2.x, 3.x, and 4.x through 4.8. Due to incorrect data management, it is vulnerable to information disclosure when processing HTTP Digest Authentication. Nonce tokens contain the raw byte value of a pointer that sits within heap memory allocation. This information reduces ASLR protections and may aid attackers isolating memory areas to target for remote code execution attacks.
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Analysis
by VulDB Data Team • 02/28/2024
The vulnerability identified as CVE-2019-18679 represents a critical information disclosure flaw affecting Squid proxy servers across multiple versions including 2.x, 3.x, and 4.x through 4.8. This issue stems from improper handling of HTTP Digest Authentication mechanisms where nonce tokens are generated using raw pointer values from heap memory allocation. The flaw occurs during the authentication process when Squid creates nonce values that directly incorporate memory addresses rather than secure random values, creating a predictable pattern that can be exploited by attackers. The vulnerability specifically impacts the security model of the proxy server by exposing sensitive memory layout information that should remain hidden from external parties.
The technical implementation of this vulnerability involves the generation of nonce tokens within the HTTP Digest Authentication framework where the system fails to properly randomize or obscure memory addresses used in token creation. When Squid processes authentication requests, it creates nonce values that contain the actual byte representation of memory pointers, which are typically located within heap memory allocations. These pointer values, when exposed in nonce tokens, provide attackers with direct insight into the memory layout of the running process, effectively reducing the effectiveness of modern exploit mitigation techniques. The exposure of heap memory addresses creates a significant reduction in address space layout randomization protections that are fundamental to modern operating system security models.
The operational impact of this vulnerability extends beyond simple information disclosure, as it directly undermines the security foundations of systems relying on Squid for proxy services. Attackers who can observe these nonce tokens can use the exposed memory addresses to bypass ASLR protections that are designed to randomize memory locations and prevent successful exploitation of memory corruption vulnerabilities. This information disclosure creates a pathway for sophisticated attackers to develop more targeted exploitation techniques, potentially leading to remote code execution attacks. The vulnerability is particularly concerning in environments where Squid serves as a critical network component for authentication and access control, as it provides attackers with the precise memory layout information needed to craft effective exploits against other vulnerabilities that may exist within the same system.
Organizations affected by this vulnerability should implement immediate mitigations including updating to patched versions of Squid where available, configuring the proxy server to use stronger randomization for nonce generation, and implementing additional monitoring for suspicious authentication patterns. The flaw aligns with CWE-200, which addresses information exposure, and represents a specific case of improper information protection within authentication mechanisms. From an ATT&CK perspective, this vulnerability relates to T1566, which covers credential access through exploitation of authentication systems, and T1068, which involves local privilege escalation through exploitation of system vulnerabilities. Security professionals should also consider implementing network segmentation and access controls to limit the potential impact of successful exploitation attempts, while monitoring for unusual authentication traffic patterns that might indicate exploitation of this vulnerability.