CVE-2019-3570 in HHVM
Summary
by MITRE
Call to the scrypt_enc() function in HHVM can lead to heap corruption by using specifically crafted parameters (N, r and p). This happens if the parameters are configurable by an attacker for instance by providing the output of scrypt_enc() in a context where Hack/PHP code would attempt to verify it by re-running scrypt_enc() with the same parameters. This could result in information disclosure, memory being overwriten or crashes of the HHVM process. This issue affects versions 4.3.0, 4.4.0, 4.5.0, 4.6.0, 4.7.0, 4.8.0, versions 3.30.5 and below, and all versions in the 4.0, 4.1, and 4.2 series.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 11/01/2023
The vulnerability described in CVE-2019-3570 represents a critical heap corruption issue within Facebook's HHVM (HipHop Virtual Machine) that processes Hack and PHP code. This flaw specifically targets the scrypt_enc() function, which implements the scrypt key derivation function commonly used for password hashing and cryptographic operations. The vulnerability arises from inadequate parameter validation within the heap allocation routines that handle the scrypt algorithm's resource requirements. When attacker-controlled parameters N, r, and p are passed to scrypt_enc(), the function fails to properly validate these values against reasonable bounds, leading to improper memory allocation that can result in heap corruption.
The technical exploitation of this vulnerability occurs when the scrypt_enc() function receives specially crafted parameters that cause memory allocation calculations to overflow or underflow, creating conditions where heap memory can be overwritten or corrupted. The parameters N, r, and p control the computational cost and memory requirements of the scrypt algorithm, with N representing the CPU/memory cost, r the block size, and p the parallelization factor. When these values exceed safe thresholds or fall below minimum requirements, the heap allocation logic in HHVM's implementation fails to properly handle the resulting memory operations. This can lead to memory corruption that manifests as information disclosure, arbitrary memory overwrites, or complete process crashes, depending on the specific conditions and memory layout at runtime.
The operational impact of this vulnerability is severe and far-reaching, particularly in environments where HHVM processes user-provided data or where scrypt_enc() is used in authentication contexts. An attacker who can influence the parameters passed to scrypt_enc() can potentially cause remote code execution by corrupting heap memory and overwriting function pointers or control data structures. The vulnerability affects multiple versions of HHVM spanning the 3.x and 4.x series, indicating a long-standing issue that was not properly addressed in the implementation. This makes the vulnerability particularly dangerous as it could affect a wide range of applications that rely on HHVM for web application execution, especially those handling authentication or cryptographic operations where scrypt is commonly employed.
The root cause of this vulnerability aligns with CWE-122 (Heap Overflow) and CWE-129 (Improper Validation of Array Index) categories, as the heap corruption stems from improper validation of input parameters that control memory allocation. From an attacker's perspective, this vulnerability maps to ATT&CK technique T1059.007 (Command and Scripting Interpreter: JavaScript) and T1068 (Exploitation for Privilege Escalation) when considering the potential for remote code execution. The vulnerability also relates to T1203 (Exploitation for Client Execution) when targeting web applications that process user input through HHVM. Organizations should implement immediate mitigations including patching to affected versions, parameter validation at input boundaries, and runtime monitoring for anomalous memory allocation patterns. Additionally, the vulnerability highlights the importance of proper resource validation in cryptographic implementations and demonstrates the critical need for thorough security testing of memory management functions in high-level interpreted languages.