CVE-2018-19132 in Web Proxy
Summary
by MITRE
Squid before 4.4, when SNMP is enabled, allows a denial of service (Memory Leak) via an SNMP packet.
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Analysis
by VulDB Data Team • 06/05/2023
The vulnerability identified as CVE-2018-19132 represents a memory leak flaw in the Squid proxy server software affecting versions prior to 4.4. This issue specifically manifests when the Simple Network Management Protocol functionality is enabled within the Squid configuration, creating a persistent memory consumption problem that can ultimately lead to system instability and denial of service conditions. The vulnerability resides in the SNMP packet processing module where insufficient memory management practices allow attackers to repeatedly send specially crafted SNMP packets that cause the proxy server to continuously allocate memory without proper deallocation.
The technical implementation of this vulnerability stems from inadequate memory handling within the SNMP subsystem of Squid. When SNMP packets are received and processed, the software fails to properly release allocated memory blocks after processing, resulting in gradual memory accumulation over time. This memory leak behavior is particularly concerning because SNMP packets can be sent by any network entity with access to the Squid server's SNMP port, making the vulnerability exploitable by both internal and external attackers without requiring authentication or specialized privileges. The flaw aligns with CWE-401, which specifically addresses improper management of memory allocation and deallocation, and demonstrates how insufficient resource management can create persistent denial of service conditions.
From an operational perspective, this vulnerability poses significant risks to organizations relying on Squid as their primary proxy server solution. The memory leak gradually consumes available system resources, potentially leading to complete system crashes or service unavailability for legitimate users. Network administrators may observe increasing memory consumption over time, with the proxy server eventually becoming unresponsive or requiring manual restarts to recover functionality. The impact extends beyond simple service disruption as the memory consumption can affect other system processes and overall network performance, particularly in environments where Squid serves as a critical infrastructure component for web traffic filtering and caching operations. This vulnerability can be exploited through automated scanning tools that repeatedly send SNMP packets to identify and trigger the memory leak behavior, making it particularly dangerous in publicly accessible environments.
The mitigation strategy for CVE-2018-19132 involves immediate upgrading to Squid version 4.4 or later, which includes proper memory management fixes for the SNMP packet processing module. Organizations should also consider disabling SNMP functionality within Squid if it is not actively required for network management purposes, as this eliminates the attack surface entirely. Network segmentation and access control measures can be implemented to restrict SNMP packet access to only trusted management systems, though this approach provides only partial protection. Security monitoring should include regular memory usage checks for Squid processes to detect early signs of memory leak behavior, and automated alerting systems should be configured to notify administrators when memory consumption exceeds predefined thresholds. The vulnerability demonstrates the importance of proper memory management in network services and aligns with ATT&CK technique T1499.004, which covers network denial of service attacks through resource exhaustion, highlighting how memory leaks can serve as effective vectors for service disruption attacks.