CVE-2019-18409 : Exploit Details and Defense Strategies

The Ruby gem ruby_parser-legacy (also known as legacy) version 1.0.0 has a security vulnerability that enables local privilege escalation due to the presence of world-writable files. This vulnerability can be exploited when using the brakeman gem with a version ranging from 4.5.0 to 4.7.0, as a local user can maliciously insert code into the file ruby_parser-legacy-1.0.0/lib/ruby_parser/legacy/ruby_parser.rb.

Understanding CVE-2019-18409

The ruby_parser-legacy gem 1.0.0 for Ruby allows local privilege escalation because of world-writable files. If the brakeman gem (which has a legacy dependency) 4.5.0 through 4.7.0 is used, a local user can insert malicious code into specific files.

What is CVE-2019-18409?

The CVE-2019-18409 vulnerability involves the ruby_parser-legacy (legacy) gem version 1.0.0 for Ruby, which permits local privilege escalation due to the presence of world-writable files.

The Impact of CVE-2019-18409

This vulnerability allows a local user to escalate privileges by inserting malicious code into critical files, potentially leading to unauthorized access and control of the affected system.

Technical Details of CVE-2019-18409

The technical details of the CVE-2019-18409 vulnerability are as follows:

Vulnerability Description

The vulnerability in the ruby_parser-legacy gem version 1.0.0 allows local privilege escalation through world-writable files, enabling unauthorized users to manipulate critical files.

Affected Systems and Versions

Affected Gem: ruby_parser-legacy (legacy) version 1.0.0
Affected Dependency: brakeman gem versions 4.5.0 to 4.7.0

Exploitation Mechanism

The vulnerability can be exploited by a local user inserting malicious code into the file ruby_parser-legacy-1.0.0/lib/ruby_parser/legacy/ruby_parser.rb when using the brakeman gem within the specified version range.

Mitigation and Prevention

To address CVE-2019-18409, consider the following mitigation strategies:

Immediate Steps to Take

Update the ruby_parser-legacy gem to a patched version that addresses the vulnerability.
Upgrade the brakeman gem to a version that no longer has the dependency on the vulnerable ruby_parser-legacy gem.
Restrict file permissions to prevent unauthorized write access.

Long-Term Security Practices

Regularly monitor and audit file permissions and access controls on critical files.
Implement the principle of least privilege to restrict user access to only necessary resources.

Patching and Updates

Stay informed about security updates for the ruby_parser-legacy and brakeman gems to apply patches promptly and prevent exploitation of known vulnerabilities.