CVE-2021-39240 : What You Need to Know

HAProxy versions 2.2 before 2.2.16, 2.3 before 2.3.13, and 2.4 before 2.4.3 are affected by a URI parsing issue that can lead to unexpected character handling.

Understanding CVE-2021-39240

This CVE describes a vulnerability in HAProxy versions 2.2, 2.3, and 2.4 that can result in discrepancies between intended routing rules and the observed authority field in HTTP/2 headers.

What is CVE-2021-39240?

The vulnerability resides in the lack of ensuring expected characters in URI schemes and paths.

The Impact of CVE-2021-39240

Attackers can potentially manipulate routing rules leading to misrouted traffic.

Technical Details of CVE-2021-39240

This section delves into the specifics of the vulnerability.

Vulnerability Description

HAProxy fails to validate characters in the scheme and path of a URI, potentially causing routing inaccuracies.

Affected Systems and Versions

HAProxy 2.2 to 2.4 are affected.

Exploitation Mechanism

Attackers exploit this flaw by crafting malicious URIs with unexpected characters, influencing routing decisions.

Mitigation and Prevention

Protect systems from CVE-2021-39240 with the following measures.

Immediate Steps to Take

Update HAProxy to versions 2.2.16, 2.3.13, or 2.4.3 to mitigate the vulnerability.

Long-Term Security Practices

Regularly monitor and patch HAProxy to prevent URI-related vulnerabilities.
Implement network segmentation to limit the impact of potential misrouted traffic.
Employ deep packet inspection to detect suspicious URI patterns.

Patching and Updates

Stay informed about HAProxy security updates and apply patches promptly to address known vulnerabilities.