CVE-2021-46784 in Web Proxy
Summary
by MITRE • 07/18/2022
In Squid 3.x through 3.5.28, 4.x through 4.17, and 5.x before 5.6, due to improper buffer management, a Denial of Service can occur when processing long Gopher server responses.
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Analysis
by VulDB Data Team • 08/01/2022
The vulnerability identified as CVE-2021-46784 represents a critical buffer management flaw within the Squid proxy server software that affects multiple major versions including 3.x through 3.5.28, 4.x through 4.17, and 5.x before 5.6. This issue stems from inadequate handling of memory buffers when processing gopher protocol responses, creating a potential pathway for malicious actors to disrupt service availability. The gopher protocol, though largely deprecated in modern internet usage, remains supported by many proxy servers for legacy system compatibility and specialized applications. The flaw specifically manifests when Squid receives gopher server responses containing excessive data that exceeds predetermined buffer limits, leading to memory corruption and subsequent service disruption.
The technical implementation of this vulnerability involves improper buffer allocation and management within Squid's gopher protocol handler component. When processing gopher responses, the software fails to properly validate the length of incoming data against allocated buffer boundaries, allowing for buffer overflow conditions to occur. This mismanagement creates a scenario where maliciously crafted gopher responses can cause the proxy server to allocate insufficient memory or overwrite adjacent memory regions, ultimately resulting in process termination and complete denial of service for legitimate users. The vulnerability operates at the application layer and can be exploited through network-based attacks without requiring authentication or special privileges.
The operational impact of CVE-2021-46784 extends beyond simple service disruption as it can affect organizations relying on Squid proxy servers for content filtering, caching, and network traffic management. Organizations may experience complete loss of proxy functionality, leading to interrupted network access for all users dependent on the proxy infrastructure. This vulnerability particularly affects enterprise environments where Squid serves as a critical component of network security architecture, potentially exposing organizations to extended downtime during attack windows. The attack vector is relatively straightforward, requiring only network access to send specially crafted gopher responses to target systems, making it an attractive option for attackers seeking to disrupt services.
From a cybersecurity perspective, this vulnerability aligns with CWE-121, which describes stack-based buffer overflow conditions, and relates to ATT&CK technique T1499.004 for network denial of service attacks. Organizations should prioritize immediate patching of affected systems to address this vulnerability, as the remediation process involves updating to patched versions of Squid software that contain proper buffer management implementations. Additionally, network segmentation and access controls should be implemented to limit exposure of vulnerable proxy servers to untrusted networks, while monitoring systems should be configured to detect anomalous gopher protocol traffic patterns that may indicate exploitation attempts.
Mitigation strategies should include deploying the latest stable releases of Squid software that contain fixes for this buffer management issue, implementing network-level controls to restrict gopher protocol access where possible, and establishing comprehensive monitoring protocols to detect potential exploitation attempts. Security teams should also consider disabling gopher protocol support entirely if the functionality is not required for business operations. Regular vulnerability assessments and penetration testing should be conducted to identify similar buffer management issues within other network infrastructure components, ensuring a comprehensive approach to defending against memory corruption vulnerabilities that could lead to similar denial of service conditions.