CVE-2020-15811 Explained : Impact and Mitigation

An issue was discovered in Squid before 4.13 and 5.x before 5.0.4, allowing HTTP Request Splitting attacks that can lead to cache poisoning.

Understanding CVE-2020-15811

What is CVE-2020-15811?

Squid before versions 4.13 and 5.x before 5.0.4 is vulnerable to HTTP Request Splitting attacks due to incorrect data validation. This vulnerability allows attackers to poison caches, compromising downstream systems.

The Impact of CVE-2020-15811

The vulnerability enables attackers to bypass local security measures, poison browser caches, and corrupt downstream caches with content from unauthorized sources.

Technical Details of CVE-2020-15811

Vulnerability Description

Incorrect data validation in Squid before 4.13 and 5.x before 5.0.4 allows HTTP Request Splitting attacks.
Attackers can hide a second request inside Transfer-Encoding, leading to cache poisoning.

Affected Systems and Versions

Squid versions before 4.13 and 5.x before 5.0.4 are affected.

Exploitation Mechanism

Squid uses a string search instead of parsing the Transfer-Encoding header, allowing attackers to split requests and corrupt downstream caches.

Mitigation and Prevention

Immediate Steps to Take

Update Squid to version 4.13 or 5.0.4 to mitigate the vulnerability.
Monitor and validate HTTP requests for any suspicious activity.

Long-Term Security Practices

Implement secure coding practices to prevent data validation issues.
Regularly update and patch software to address known vulnerabilities.
Conduct security audits and penetration testing to identify and remediate weaknesses.

Patching and Updates

Apply patches provided by Squid to fix the vulnerability and enhance system security.