CVE-2021-33580 : What You Need to Know

Apache Roller, an open-source blog server software, was found to be vulnerable to a regex injection leading to Denial of Service (DoS) attack. The vulnerability allowed an attacker to exploit user-controlled input to cause a Regex Catastrophic Backtracking, resulting in server-side ReDoS attacks.

Understanding CVE-2021-33580

This CVE refers to a security vulnerability in Apache Roller where user-controlled input is manipulated to trigger a DoS attack through regex injection.

What is CVE-2021-33580?

The CVE-2021-33580 vulnerability in Apache Roller occurs due to the use of user-controlled input to build and execute a regex expression. This can be exploited by an attacker to cause a ReDoS attack on the server.

The Impact of CVE-2021-33580

The impact of CVE-2021-33580 is considered low as the attack only works if Banned-words Referrer processing is enabled in Roller and is off-by-default.

Technical Details of CVE-2021-33580

The vulnerability stems from the use of user-controlled data in constructing regex expressions within Apache Roller.

Vulnerability Description

User-controlled data such as

request.getHeader("Referer")

,

request.getRequestURL()

, and

request.getQueryString()

are leveraged to create and run a regex expression, leading to potential ReDoS attacks.

Affected Systems and Versions

Apache Roller versions prior to 6.0.2 are affected by this vulnerability.

Exploitation Mechanism

Attackers can programmatically send crafted headers to exploit the regex injection vulnerability, causing the server-side ReDoS.

Mitigation and Prevention

To mitigate the CVE-2021-33580 vulnerability in Apache Roller, immediate actions and long-term security practices can be implemented.

Immediate Steps to Take

Upgrade to the fixed version, Roller 6.0.2, to address the vulnerability. If upgrading is not feasible, consider implementing workarounds.

Long-Term Security Practices

Disable Banned-Words Referrer processing if you are concerned about potential DoS attacks. Review and adjust server configurations for enhanced security measures.

Patching and Updates

Ensure timely patching of the Apache Roller software to the latest version to prevent exploitation of known vulnerabilities.