CVE-2021-43804 : Exploit Details and Defense Strategies

An out-of-bounds read vulnerability in parsing RTCP BYE messages in PJSIP

Understanding CVE-2021-43804

PJSIP is an open-source multimedia communication library that implements various standard-based protocols. This CVE involves an out-of-bounds read issue when processing RTCP BYE messages in PJSIP, potentially leading to security concerns.

What is CVE-2021-43804?

In affected versions of PJSIP, when an incoming RTCP BYE message contains a reason's length that is not checked against the actual packet size, it could result in an out-of-bound read access vulnerability. This vulnerability impacts users utilizing PJMEDIA and RTCP, allowing a malicious actor to exploit the flaw by sending a RTCP BYE message with an invalid reason length.

The Impact of CVE-2021-43804

The impact of this vulnerability is rated as HIGH with a base score of 7.3 under CVSS v3.1. It can lead to unauthorized access to sensitive information, potentially compromising the confidentiality, integrity, and availability of the affected systems.

Technical Details of CVE-2021-43804

This section provides detailed technical information about the vulnerability.

Vulnerability Description

The vulnerability arises from the lack of validation of the reason's length in RTCP BYE messages, enabling an attacker to trigger an out-of-bounds read access.

Affected Systems and Versions

Vendor: pjsip
Product: pjproject
Versions Affected: <= 2.11.1

Exploitation Mechanism

The exploitation involves sending a malicious RTCP BYE message with an incorrect reason length to trigger the out-of-bounds read vulnerability.

Mitigation and Prevention

To address CVE-2021-43804, users should take immediate and long-term security measures.

Immediate Steps to Take

Upgrade to a fixed version (beyond 2.11.1).

Long-Term Security Practices

Regularly monitor and update the PJSIP library.
Implement network segmentation and access controls.
Conduct regular security assessments and audits.

Patching and Updates

Ensure timely application of security patches from the vendor to mitigate the vulnerability.