CVE-2019-3556 Explained : Impact and Mitigation

HHVM has a vulnerability that allows malicious users to overwrite files due to improper validation of a parameter in the "dump-pcre-cache" request handler.

Understanding CVE-2019-3556

This CVE affects HHVM versions prior to 4.56.2, versions 4.57.0 to 4.78.0, 4.79.0, 4.80.0, 4.81.0, 4.82.0, and 4.83.0.

What is CVE-2019-3556?

HHVM's "admin" server feature includes a request handler called "dump-pcre-cache" that lacks validation on a parameter, allowing malicious users to overwrite files.

The Impact of CVE-2019-3556

This vulnerability can be exploited by attackers to overwrite any files that the user running HHVM has write access to, potentially leading to unauthorized access or data loss.

Technical Details of CVE-2019-3556

HHVM versions are affected based on the following criteria:

Versions prior to 4.56.2
Versions 4.57.0 to 4.78.0
Versions 4.79.0, 4.80.0, 4.81.0, 4.82.0, and 4.83.0

Vulnerability Description

The issue arises from the lack of validation on a parameter in the "dump-pcre-cache" request handler within HHVM's "admin" server, enabling file overwriting.

Affected Systems and Versions

HHVM versions prior to 4.56.2
HHVM versions 4.57.0 to 4.78.0
HHVM versions 4.79.0, 4.80.0, 4.81.0, 4.82.0, and 4.83.0

Exploitation Mechanism

Malicious users can exploit the vulnerability by manipulating the parameter in the "dump-pcre-cache" request handler to overwrite files accessible to the HHVM user.

Mitigation and Prevention

To address CVE-2019-3556, consider the following steps:

Immediate Steps to Take

Update HHVM to a patched version that addresses the vulnerability.
Restrict access to the affected server to trusted users only.

Long-Term Security Practices

Regularly monitor and audit file system changes and permissions.
Implement least privilege access controls to limit potential damage from file overwriting.

Patching and Updates

Apply security patches provided by Facebook for HHVM to fix the vulnerability and prevent exploitation.