Source: cve-assign@fb.com
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).
HHVM (HipHop Virtual Machine) is vulnerable to an out-of-bounds read via the Memcache::getextendedstats function, allowing attackers to potentially leak sensitive information or crash the service. Exploiting this requires control over memcached server hostnames and/or ports, making it a targeted attack vector. This vulnerability impacts all supported versions of HHVM up to and including 3.30 and 3.27.4.
Step 1: Target Identification: The attacker identifies HHVM instances running and determines the versions.
Step 2: Memcached Server Control: The attacker either controls a memcached server or has the ability to inject malicious memcached server hostnames and/or ports into the HHVM configuration or application logic.
Step 3: Triggering the Vulnerability: The attacker crafts a request that calls the Memcache::getextendedstats function, directing it to the malicious memcached server.
Step 4: Malicious Response: The attacker's memcached server responds with a crafted response containing data designed to exceed the buffer allocated by HHVM.
Step 5: Out-of-Bounds Read: HHVM's Memcache::getextendedstats function attempts to process the malicious response, leading to an out-of-bounds read.
Step 6: Impact: The out-of-bounds read can result in information disclosure (leaking sensitive data from memory), denial of service (crashing the HHVM process), or potentially, in a highly complex scenario, remote code execution.
The vulnerability lies within the Memcache::getextendedstats function in HHVM. The function, when interacting with a memcached server, fails to properly validate the size of the data returned by the server. This leads to an out-of-bounds read when the function attempts to access memory beyond the allocated buffer. The root cause is a lack of bounds checking on the data received from the memcached server, allowing a malicious memcached server (or a compromised one) to provide crafted responses that trigger the read. This could lead to information disclosure, denial of service, or potentially remote code execution if combined with other vulnerabilities. The vulnerability is triggered by providing a malicious memcached server hostname or port, allowing an attacker to control the response data.
While no specific APTs are directly linked to this CVE, the vulnerability's nature makes it attractive for any attacker seeking information disclosure or denial of service. Attackers could leverage this vulnerability in conjunction with other vulnerabilities to achieve more significant impacts. The lack of a CISA KEV listing does not diminish the risk. This vulnerability is not currently listed on CISA's Known Exploited Vulnerabilities (KEV) catalog.
Monitor network traffic for unusual connections to memcached servers, especially those originating from HHVM instances.
Analyze HHVM logs for errors related to memory access or unexpected behavior when interacting with memcached.
Implement intrusion detection system (IDS) rules to identify malicious memcached responses based on known exploit patterns.
Monitor for unexpected process crashes or restarts of HHVM services.
Examine HHVM configuration files for suspicious memcached server hostnames or ports.
Upgrade HHVM to a patched version (3.31 or later, or 3.27.5 or later).
Restrict access to memcached servers. Implement network segmentation to limit the reach of compromised memcached servers.
Carefully review and validate all memcached server hostnames and ports used by HHVM applications.
Implement input validation to sanitize and filter any user-supplied data that might be used to configure memcached connections.
Regularly audit HHVM configurations for unauthorized changes.
Consider using a Web Application Firewall (WAF) to filter malicious requests.