CVE-2021-39191 Explained : Impact and Mitigation

This CVE record details an Open Redirect vulnerability in mod_auth_openidc versions prior to 2.4.9.4, allowing attackers to redirect users to untrusted sites.

Understanding CVE-2021-39191

This section provides insights into the nature and impact of the CVE-2021-39191 vulnerability.

What is CVE-2021-39191?

CVE-2021-39191 is an Open Redirect vulnerability in mod_auth_openidc, an authentication/authorization module for Apache 2.x HTTP server. Attackers can exploit this vulnerability by manipulating the

target_link_uri

parameter to redirect users to malicious sites.

The Impact of CVE-2021-39191

The impact of this CVE includes potential user redirection to unauthorized and malicious websites, leading to phishing attacks or the installation of malware.

Technical Details of CVE-2021-39191

This section delves into the technical aspects of the CVE-2021-39191 vulnerability.

Vulnerability Description

The vulnerability in mod_auth_openidc prior to version 2.4.9.4 enables an open redirect attack by accepting crafted URLs in the

target_link_uri

parameter.

Affected Systems and Versions

Affected Vendor: zmartzone
Affected Product: mod_auth_openidc
Vulnerable Versions: <=2.4.9.3

Exploitation Mechanism

The vulnerability is exploited by supplying a malicious URL in the

target_link_uri

parameter, allowing attackers to redirect users to external sites.

Mitigation and Prevention

Explore the actions necessary to mitigate and prevent exploitation of CVE-2021-39191.

Immediate Steps to Take

Upgrade mod_auth_openidc to version 2.4.9.4 or later to apply the required

OIDCRedirectURLsAllowed

setting.

Long-Term Security Practices

Implement input validation mechanisms for URL parameters to prevent injection attacks.
Educate users on verifying URLs before following redirects.

Patching and Updates

Regularly check for security advisories from zmartzone for updates and patches to address vulnerabilities.