CVE-2009-3826 in squidGuard
Summary
by MITRE
Multiple buffer overflows in squidGuard 1.4 allow remote attackers to bypass intended URL blocking via a long URL, related to (1) the relationship between a certain buffer size in squidGuard and a certain buffer size in Squid and (2) a redirect URL that contains information about the originally requested URL.
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Analysis
by VulDB Data Team • 03/20/2025
The vulnerability identified as CVE-2009-3826 represents a critical buffer overflow issue affecting squidGuard version 1.4, a popular web content filtering tool widely deployed in enterprise environments for controlling access to specific websites. This vulnerability arises from improper handling of URL lengths within the squidGuard application, creating a scenario where remote attackers can exploit the software's buffer management to circumvent content filtering policies. The flaw specifically impacts organizations relying on squidGuard for network security and compliance, potentially allowing unauthorized access to blocked websites and undermining the security posture of filtered networks.
The technical root cause of this vulnerability stems from a mismatch between buffer sizes in squidGuard and the underlying Squid proxy server, creating a condition where input validation fails when processing excessively long URLs. When a maliciously crafted URL exceeds the allocated buffer capacity in squidGuard's processing routines, the application experiences buffer overflow conditions that can be manipulated to overwrite memory segments. This occurs because squidGuard does not properly validate or truncate URL lengths before processing, particularly when handling redirect URLs that contain encoded information about the originally requested website. The relationship between these buffer sizes creates a predictable overflow pattern that attackers can exploit through carefully constructed URL sequences.
The operational impact of this vulnerability extends beyond simple bypass of content filtering, as it can enable attackers to access restricted websites, potentially leading to data exfiltration, malware delivery, or other malicious activities. Organizations using squidGuard for security policy enforcement face significant risk since the vulnerability allows remote code execution or complete bypass of filtering mechanisms without requiring authentication. This makes it particularly dangerous in corporate environments where squidGuard is used to prevent access to social media, gambling sites, or other potentially harmful content. The vulnerability's remote exploitability means that attackers can leverage this weakness from outside the network perimeter, making it a critical concern for network security teams.
Mitigation strategies for CVE-2009-3826 should prioritize immediate patching of squidGuard installations to version 1.4.1 or later, which contains the necessary buffer size adjustments and input validation improvements. Network administrators should also implement additional monitoring for unusual URL patterns and implement stricter input validation at the proxy level to detect and prevent exploitation attempts. The vulnerability aligns with CWE-121, which addresses stack-based buffer overflow conditions, and relates to ATT&CK technique T1071.004 for application layer protocol manipulation. Organizations should conduct thorough security assessments of their proxy configurations and consider implementing network segmentation to limit the impact of potential exploitation, while also ensuring that all proxy server components maintain consistent buffer management practices to prevent similar vulnerabilities in the future.