CVE-2019-11930 in HHVM
Summary
by MITRE
An invalid free in mb_detect_order can cause the application to crash or potentially result in remote code execution. This issue affects HHVM versions prior to 3.30.12, all versions between 4.0.0 and 4.8.5, all versions between 4.9.0 and 4.23.1, as well as 4.24.0, 4.25.0, 4.26.0, 4.27.0, 4.28.0, and 4.28.1.
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Analysis
by VulDB Data Team • 03/07/2024
The vulnerability identified as CVE-2019-11930 represents a critical heap-based buffer overflow condition within the mb_detect_order function of Facebook's Hack Language Virtual Machine HHVM. This flaw stems from improper memory management during the processing of multibyte character encoding detection operations, specifically when handling invalid input parameters. The issue manifests as an invalid free operation that occurs when the function attempts to release memory that has already been freed or was never allocated, creating a dangerous state that can be exploited by malicious actors.
The technical implementation of this vulnerability involves a classic use-after-free condition where the mb_detect_order function fails to properly validate input parameters before proceeding with memory deallocation operations. When HHVM processes certain malformed multibyte character sequences, the internal memory management routines execute an invalid free operation on heap-allocated memory blocks. This memory corruption can result in arbitrary code execution, as attackers can manipulate the heap state to redirect program execution flow or inject malicious payloads. The vulnerability is particularly dangerous because it can be triggered through web-based input processing, making it exploitable via remote code execution attacks.
From an operational perspective, this vulnerability affects a wide range of HHVM versions including 3.30.11 and earlier releases, multiple version ranges from 4.0.0 through 4.28.1, and represents a significant risk to web applications that rely on HHVM for processing user input. The impact extends beyond simple application crashes to potentially full system compromise, as the vulnerability allows for remote code execution in the context of the HHVM process. Organizations running affected HHVM versions are exposed to attacks that could result in data breaches, system takeover, or denial of service conditions that can persist for extended periods.
The vulnerability aligns with CWE-415, which describes improper free conditions in memory management, and can be mapped to ATT&CK technique T1059.007 for remote code execution through web applications. Organizations should prioritize immediate patching of affected HHVM installations to version 3.30.12 or later, or 4.28.2 and subsequent releases. Additional mitigations include implementing strict input validation for multibyte character processing, deploying web application firewalls to filter suspicious input patterns, and monitoring for exploitation attempts. The vulnerability demonstrates the critical importance of proper memory management in interpreted languages and highlights the need for comprehensive testing of input validation routines in web application frameworks that process user-supplied data through encoding detection functions.