CVE-2021-27921 Explained : Impact and Mitigation

Pillow before 8.1.1 is impacted by CVE-2021-27921, allowing attackers to cause a denial of service due to improper memory consumption handling. Here's what you need to know about this vulnerability.

Understanding CVE-2021-27921

Pillow, a popular Python Imaging Library, contains a vulnerability that can lead to a denial of service attack due to unchecked image size within a BLP container.

What is CVE-2021-27921?

Pillow before version 8.1.1 is susceptible to a denial of service attack caused by unchecked image size, which can result in significant memory allocation attempts that exhaust resources.

The Impact of CVE-2021-27921

The impact of this vulnerability is the potential for attackers to exploit the improperly checked image size to consume excessive memory resources, leading to a denial of service condition.

Technical Details of CVE-2021-27921

Here are the technical details associated with CVE-2021-27921:

Vulnerability Description

The vulnerability in Pillow before 8.1.1 arises from the failure to properly validate the image size within a BLP container, allowing for extremely large memory allocations.

Affected Systems and Versions

All versions of Pillow before 8.1.1 are affected by this vulnerability.

Exploitation Mechanism

Attackers can exploit this vulnerability by crafting malicious images with manipulated size parameters, triggering excessive memory consumption when processed by Pillow.

Mitigation and Prevention

To protect systems from the CVE-2021-27921 vulnerability, consider the following mitigation strategies:

Immediate Steps to Take

Upgrade Pillow to version 8.1.1 or newer to address the vulnerability.
Implement input validation routines to verify image sizes before processing.

Long-Term Security Practices

Regularly update libraries and dependencies to the latest secure versions.
Conduct security testing and code reviews to identify and address vulnerabilities proactively.

Patching and Updates

Monitor security advisories and promptly apply patches released by Pillow to ensure ongoing protection against known vulnerabilities.