CVE-2020-28024 : Exploit Details and Defense Strategies

Exim 4 before 4.94.2 allows Buffer Underwrite that may result in unauthenticated remote attackers executing arbitrary commands.

Understanding CVE-2020-28024

What is CVE-2020-28024?

Exim 4 before 4.94.2 is vulnerable to Buffer Underwrite, enabling unauthenticated remote attackers to execute arbitrary commands.

The Impact of CVE-2020-28024

The vulnerability allows attackers to execute arbitrary commands remotely due to improper handling of characters by smtp_ungetc.

Technical Details of CVE-2020-28024

Vulnerability Description

Exim 4 before 4.94.2 allows Buffer Underwrite, potentially leading to remote code execution by unauthenticated attackers.

Affected Systems and Versions

Product: Not applicable
Vendor: Not applicable
Versions: All versions before 4.94.2

Exploitation Mechanism

The issue arises from smtp_ungetc, which was designed to push back characters but can inadvertently push back non-character error codes like EOF.

Mitigation and Prevention

Immediate Steps to Take

Update Exim to version 4.94.2 or later to mitigate the vulnerability.
Monitor for any unusual network activity that could indicate exploitation.

Long-Term Security Practices

Regularly update and patch Exim to protect against known vulnerabilities.
Implement network segmentation and access controls to limit the attack surface.

Patching and Updates

Ensure timely installation of security patches and updates to Exim to address vulnerabilities.