CVE-2018-6340 in HHVM
Summary
by MITRE
The Memcache::getextendedstats function can be used to trigger an out-of-bounds read. Exploiting this issue requires control over memcached server hostnames and/or ports. This affects all supported versions of HHVM (3.30 and 3.27.4 and below).
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Analysis
by VulDB Data Team • 05/06/2025
The vulnerability identified as CVE-2018-6340 represents a critical out-of-bounds read flaw within the Memcache::getextendedstats function implementation in HHVM environments. This issue stems from insufficient input validation and memory management within the memcached client library integration, specifically affecting HHVM versions 3.30 and earlier releases including 3.27.4 and below. The flaw manifests when the getextendedstats function processes server hostnames and port information, creating a scenario where arbitrary memory access can occur beyond the intended buffer boundaries.
The technical exploitation of this vulnerability requires an attacker to gain control over memcached server hostnames and/or ports, which provides the necessary precondition for triggering the out-of-bounds memory read. This attack vector aligns with CWE-125, which describes out-of-bounds read conditions that occur when a program accesses memory beyond the bounds of a buffer. The vulnerability essentially allows an attacker to read memory contents that should remain protected, potentially exposing sensitive data such as authentication tokens, session information, or other confidential application data stored in memory. The memory corruption occurs during the processing of extended statistics requests, where the function fails to properly validate the length of server identifiers before attempting to read from allocated memory regions.
The operational impact of this vulnerability extends beyond simple information disclosure, as it can enable more sophisticated attacks including remote code execution under certain conditions. When combined with other vulnerabilities or attack vectors, this out-of-bounds read can serve as a stepping stone for attackers to gain deeper system access. The affected HHVM versions represent a significant portion of production environments that may be vulnerable, particularly in web applications that rely heavily on memcached for session management, caching, and distributed data storage. This vulnerability directly impacts the integrity and confidentiality of applications running on HHVM platforms, as it allows for unauthorized memory access that could compromise the entire application stack.
Mitigation strategies for CVE-2018-6340 primarily focus on immediate version upgrades to HHVM 3.31 or later, which contain the necessary patches to address the memory access violation. Organizations should also implement network segmentation to limit access to memcached servers and restrict hostname/port manipulation capabilities within application code. Additionally, input validation should be strengthened at all layers where memcached server information is processed, ensuring that hostname and port values are properly sanitized before being passed to the getextendedstats function. Security monitoring should be enhanced to detect unusual patterns in memcached statistics requests that might indicate exploitation attempts. This vulnerability demonstrates the importance of proper memory management in interpreted languages and highlights the need for comprehensive security testing of third-party library integrations, particularly those handling network communications and data processing in high-security environments. The ATT&CK framework categorizes this as a memory corruption technique under the system binary modification and privilege escalation domains, emphasizing its potential for both information gathering and system compromise.