CVE-2021-27850 : What You Need to Know

A critical unauthenticated remote code execution vulnerability affecting multiple versions of Apache Tapestry has been discovered. The vulnerability allows attackers to bypass the fix for CVE-2019-0195, potentially leading to remote code execution.

Understanding CVE-2021-27850

Apache Tapestry is impacted by a critical unauthenticated remote code execution vulnerability that affects versions 5.4.5, 5.5.0, 5.6.2, and 5.7.0. The discovery of this vulnerability highlights a serious security risk that could enable attackers to execute arbitrary code remotely.

What is CVE-2021-27850?

CVE-2021-27850 is a critical unauthenticated remote code execution vulnerability found in recent versions of Apache Tapestry, including 5.4.5, 5.5.0, 5.6.2, and 5.7.0. It allows attackers to bypass the fix for CVE-2019-0195, potentially leading to the execution of arbitrary code remotely.

The Impact of CVE-2021-27850

The vulnerability poses a significant security risk as it enables unauthenticated attackers to execute remote code on affected systems. By exploiting this vulnerability, attackers could potentially compromise the integrity and confidentiality of sensitive data stored on the system.

Technical Details of CVE-2021-27850

The vulnerability involves the bypass of a fix implemented for CVE-2019-0195 in Apache Tapestry. Attackers can exploit this vulnerability to execute arbitrary code remotely, bypassing security measures put in place to mitigate similar risks.

Vulnerability Description

Before the fix for CVE-2019-0195, attackers could download arbitrary class files by crafting specific asset file URLs. Despite the implementation of a blacklist filter, attackers can append a forward slash to a URL to bypass the filter and load malicious files into the response, potentially leading to remote code execution.

Affected Systems and Versions

Versions of Apache Tapestry affected by CVE-2021-27850 include 5.4.5, 5.5.0, 5.6.2, and 5.7.0. Users of these versions are at risk of exploitation by malicious actors attempting to execute arbitrary code remotely.

Exploitation Mechanism

By appending a forward slash to a crafted URL, attackers can exploit a flaw in the blacklist filter, enabling the loading of malicious class files. This manipulation can lead to the execution of arbitrary code, compromising system security.

Mitigation and Prevention

It is crucial for Apache Tapestry users to take immediate action to mitigate the risks posed by CVE-2021-27850. Implementing security patches and following recommended security practices can help prevent potential exploitation.

Immediate Steps to Take

Users of Apache Tapestry versions 5.4.0 to 5.6.1 are advised to upgrade to version 5.6.2 or later. Similarly, users of version 5.7.0 should upgrade to version 5.7.1 or later to address the vulnerability and enhance system security.

Long-Term Security Practices

In addition to applying immediate patches, users should adopt long-term security practices such as regular security updates, vulnerability assessments, and security monitoring to safeguard against potential threats.

Patching and Updates

Regularly checking for updates and applying patches provided by Apache Tapestry is essential to address known vulnerabilities and enhance the overall security posture of the system.