CVE-2019-11596 in Memcached
Summary
by MITRE
In memcached before 1.5.14, a NULL pointer dereference was found in the "lru mode" and "lru temp_ttl" commands. This causes a denial of service when parsing crafted lru command messages in process_lru_command in memcached.c.
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Analysis
by VulDB Data Team • 09/11/2023
The vulnerability CVE-2019-11596 represents a critical denial of service flaw in memcached versions prior to 1.5.14, specifically affecting the memory management subsystem through improper handling of LRU (Least Recently Used) command parsing. This issue manifests when memcached processes crafted LRU command messages that trigger a NULL pointer dereference during the execution of process_lru_command function in memcached.c, fundamentally compromising the server's ability to maintain operations. The flaw exists within the lru mode and lru temp_ttl command implementations, which are core components of memcached's memory allocation and eviction strategies.
The technical nature of this vulnerability stems from inadequate input validation and error handling within the memcached memory management system. When maliciously crafted LRU commands are received, the process_lru_command function fails to properly check for NULL pointer conditions before attempting to dereference memory addresses, leading to immediate process termination and system unavailability. This represents a classic CWE-476 Null Pointer Dereference vulnerability where the application assumes pointer values will always be valid without proper validation. The attack vector requires only sending specially crafted commands to the memcached service, making it particularly dangerous as it can be exploited remotely without authentication.
The operational impact of CVE-2019-11596 extends beyond simple service disruption, as memcached serves as a critical component in many high-traffic web applications, caching systems, and distributed architectures. When exploited, this vulnerability can cause cascading failures across dependent services, as memcached instances often serve as foundational caching layers for databases, web applications, and microservices. The denial of service effect can be particularly severe in environments where memcached is used for session storage, content caching, or as a distributed cache for application data, potentially affecting thousands of users simultaneously. Organizations relying on memcached for performance optimization face significant risk of service degradation or complete outages when this vulnerability is exploited.
Mitigation strategies for CVE-2019-11596 primarily focus on immediate patching of affected memcached installations to version 1.5.14 or later, which contains the necessary fixes for proper NULL pointer validation in LRU command processing. Network-level protections should include implementing firewall rules to restrict memcached service access to trusted networks only, as the vulnerability can be exploited remotely. Additionally, monitoring systems should be configured to detect unusual command patterns or service disruptions that may indicate exploitation attempts. Organizations should also consider implementing redundant caching layers and failover mechanisms to minimize the impact of potential service interruptions. From an ATT&CK framework perspective, this vulnerability maps to T1499.004 Network Denial of Service and T1595.001 Network Configuration, as it exploits weaknesses in network service configuration and can be used to disrupt availability of caching infrastructure.