CVE-2020-8449 in Web Proxy
Summary
by MITRE
An issue was discovered in Squid before 4.10. Due to incorrect input validation, it can interpret crafted HTTP requests in unexpected ways to access server resources prohibited by earlier security filters.
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Analysis
by VulDB Data Team • 03/28/2024
The vulnerability identified as CVE-2020-8449 represents a critical input validation flaw within the Squid proxy server software that affects versions prior to 4.10. This issue stems from inadequate sanitization of HTTP request data which allows malicious actors to craft specially formatted requests that bypass existing security controls and access restricted server resources. The flaw specifically manifests in how Squid processes certain HTTP headers and request parameters, creating a pathway for unauthorized access that circumvents the intended security filtering mechanisms. This vulnerability is particularly concerning because it directly undermines the fundamental security model of proxy servers which are designed to act as intermediaries that enforce access controls and filter malicious traffic.
The technical implementation of this vulnerability involves improper handling of HTTP request parsing where Squid fails to properly validate and sanitize input data before processing it through its internal filtering system. Attackers can exploit this weakness by constructing HTTP requests that contain crafted parameters or headers that the proxy server interprets in unexpected ways. This misinterpretation allows the proxy to bypass earlier security checks that would normally prevent access to restricted resources, effectively creating a backdoor mechanism within the proxy server's normal operation. The flaw operates at the application layer and specifically targets the HTTP request processing pipeline where the proxy server evaluates access control rules and security policies.
From an operational impact perspective, this vulnerability creates significant risks for organizations that rely on Squid as their primary proxy server solution. The ability to bypass security filters means that attackers can potentially access internal resources, sensitive data, or systems that should be protected by the proxy server's access control mechanisms. This vulnerability can be exploited to gain unauthorized access to corporate networks, internal databases, or restricted web services that are typically protected by the proxy server's security policies. The impact extends beyond simple unauthorized access as it can enable further exploitation including potential data exfiltration, lateral movement within networks, or the establishment of persistent access points. The vulnerability affects both web browsing and application traffic that passes through the proxy server, making it a comprehensive threat to network security.
Organizations should immediately implement mitigations including upgrading to Squid version 4.10 or later where the input validation issues have been addressed. The fix typically involves enhanced validation of HTTP request parameters and headers to ensure that malformed or crafted inputs are properly rejected before they can influence the proxy server's access control decisions. Security teams should also conduct comprehensive audits of their proxy server configurations to identify any potential workarounds or custom rules that might be vulnerable to similar exploitation techniques. Network monitoring should be enhanced to detect unusual patterns of access that might indicate exploitation attempts. Additionally, organizations should consider implementing additional security controls such as web application firewalls or intrusion detection systems that can detect and block the specific patterns of malicious requests associated with this vulnerability. This vulnerability aligns with CWE-20, which addresses improper input validation, and represents a clear example of how insufficient sanitization can lead to privilege escalation and access control bypass scenarios. The ATT&CK framework categorizes this as a technique involving bypassing security controls through manipulation of application inputs, making it particularly relevant to defensive strategies focused on application layer security and proxy server hardening.