CVE-2021-21276 Explained : Impact and Mitigation
CVE-2021-21276 allows attackers to gain admin access to Polr site instances without an existing account. Learn the impact, technical details, and mitigation steps.
Polr is an open-source URL shortener that was found to have a privilege escalation vulnerability before version 2.3.0. Attackers could exploit a weakness in the setup process to gain admin access to site instances without needing an existing account. The loose comparison (==) in SetupController made it susceptible to attacks, allowing attackers to craft requests with specific cookie headers to the /setup/finish endpoint and potentially obtain admin privileges.
Understanding CVE-2021-21276
This CVE highlights a critical vulnerability in Polr versions prior to 2.3.0 that could lead to privilege escalation.
What is CVE-2021-21276?
CVE-2021-21276 is a privilege escalation vulnerability in the setup process of Polr URL shortener before version 2.3.0. It allows attackers to gain unauthorized admin access even without an existing account.
The Impact of CVE-2021-21276
The exploitation of this vulnerability could result in attackers obtaining admin privileges on Polr site instances, posing a significant security risk to affected systems.
Technical Details of CVE-2021-21276
The vulnerability is primarily due to a loose comparison (==) in the SetupController, which can be exploited by attackers to escalate privileges.
Vulnerability Description
The vulnerability in Polr versions prior to 2.3.0 allows attackers to perform unauthorized administrative actions by manipulating specific cookie headers in requests to the /setup/finish endpoint.
Affected Systems and Versions
Vendor: cydrobolt, Product: polr Affected Version: < 2.3.0
Exploitation Mechanism
By crafting requests with specific cookie headers, attackers can trigger the vulnerability and potentially gain unauthorized admin privileges on the Polr instance.
Mitigation and Prevention
To mitigate the CVE-2021-21276 vulnerability:
Immediate Steps to Take
Users are advised to update Polr to version 2.3.0 or later to eliminate the privilege escalation risk. Alternatively, a temporary fix involves adding 'abort(404)' to the first line of finishSetup in SetupController.php.
Long-Term Security Practices
It is recommended to regularly update software, implement secure coding practices, and conduct security audits to prevent similar vulnerabilities.
Patching and Updates
Ensure that Polr is updated to version 2.3.0 to apply the necessary patches and security enhancements.