CVE-2021-22969 : Exploit Details and Defense Strategies

This article provides detailed information about CVE-2021-22969, a vulnerability in Concrete CMS (formerly concrete5) versions below 8.5.7 that allows SSRF mitigation bypass using DNS Rebind attacks.

Understanding CVE-2021-22969

Concrete CMS versions below 8.5.7 are affected by a vulnerability that enables an attacker to fetch cloud IAAS (e.g., AWS) IAM keys by exploiting a SSRF mitigation bypass using DNS Rebind attacks.

What is CVE-2021-22969?

CVE-2021-22969 is a Server-Side Request Forgery (SSRF) vulnerability (CWE-918) in Concrete CMS versions below 8.5.7, allowing unauthorized access to cloud IAAS IAM keys.

The Impact of CVE-2021-22969

The vulnerability poses a moderate risk, with a CVSS 3.1 score of 3.5 (AV:N/AC:H/PR:L/UI:N/S:C/C:L/I:N/A:N). Note that misconfigurations in Cloud IAAS providers are not considered Concrete CMS vulnerabilities.

Technical Details of CVE-2021-22969

The Concrete CMS team addressed this vulnerability by implementing a fix in version 9.0.0. The fix prevents downloads from the local network and validates IP addresses for downloads instead of relying on DNS.

Vulnerability Description

The vulnerability in Concrete CMS versions below 8.5.7 allows attackers to bypass SSRF mitigation using DNS Rebind attacks to access cloud IAAS IAM keys.

Affected Systems and Versions

Concrete CMS versions 8.5.6 and below are affected by CVE-2021-22969. The vulnerability is fixed in Concrete CMS version 8.5.7 and 9.0.0.

Exploitation Mechanism

Attackers exploit the vulnerability by manipulating DNS responses to fetch cloud IAAS IAM keys, potentially leading to unauthorized access.

Mitigation and Prevention

To mitigate the risk posed by CVE-2021-22969, it is crucial to ensure that IMDS configurations align with cloud provider best practices.

Immediate Steps to Take

Organizations using vulnerable versions of Concrete CMS should update to version 8.5.7 or 9.0.0 to eliminate the risk of SSRF attacks.

Long-Term Security Practices

Regularly review and update IMDS configurations to maintain secure interaction with cloud IAAS providers.

Patching and Updates

Concrete CMS users should apply the latest patches and updates to ensure protection against known vulnerabilities.