CVE-2019-9021 Explained : Impact and Mitigation

A problem was found in earlier versions of PHP, specifically before 5.6.40, 7.x before 7.1.26, 7.2.x before 7.2.14, and 7.3.x before 7.3.1. The issue involves reading functions in the PHAR extension, which may result in a heap-based buffer over-read. This could potentially enable an attacker to access memory that is either allocated or unallocated beyond the actual data while attempting to parse the file name. It's important to note that this vulnerability is different from CVE-2018-20783. The specific area of concern is in phar_detect_phar_fname_ext, located in ext/phar/phar.c.

Understanding CVE-2019-9021

This CVE relates to a heap-based buffer over-read vulnerability in PHP versions prior to 5.6.40, 7.x before 7.1.26, 7.2.x before 7.2.14, and 7.3.x before 7.3.1.

What is CVE-2019-9021?

CVE-2019-9021 is a security vulnerability found in PHP versions before 5.6.40, 7.x before 7.1.26, 7.2.x before 7.2.14, and 7.3.x before 7.3.1. It involves a heap-based buffer over-read in the PHAR extension's reading functions.

The Impact of CVE-2019-9021

This vulnerability could allow an attacker to read allocated or unallocated memory beyond the actual data while trying to parse a file name, potentially leading to unauthorized access to sensitive information.

Technical Details of CVE-2019-9021

This section provides more in-depth technical information about the vulnerability.

Vulnerability Description

The vulnerability in PHP versions prior to 5.6.40, 7.x before 7.1.26, 7.2.x before 7.2.14, and 7.3.x before 7.3.1 allows for a heap-based buffer over-read in the PHAR extension's reading functions.

Affected Systems and Versions

PHP versions before 5.6.40
PHP 7.x before 7.1.26
PHP 7.2.x before 7.2.14
PHP 7.3.x before 7.3.1

Exploitation Mechanism

The vulnerability may be exploited by manipulating the PHAR extension's reading functions to access memory beyond the intended data, potentially leading to a heap-based buffer over-read.

Mitigation and Prevention

It is crucial to take immediate steps to address and prevent the exploitation of this vulnerability.

Immediate Steps to Take

Update PHP to versions 5.6.40, 7.1.26, 7.2.14, or 7.3.1, which contain fixes for this vulnerability.
Monitor for any unauthorized access or unusual activities on the affected systems.

Long-Term Security Practices

Regularly update PHP and other software to the latest secure versions.
Implement strong access controls and authentication mechanisms to prevent unauthorized access.

Patching and Updates

Apply patches provided by PHP to address the heap-based buffer over-read vulnerability.