CVE-2020-20341 in YzmCMS
Summary
by MITRE • 09/02/2021
YzmCMS v5.5 contains a server-side request forgery (SSRF) in the grab_image() function.
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Analysis
by VulDB Data Team • 09/05/2021
The vulnerability CVE-2020-20341 represents a critical server-side request forgery flaw within YzmCMS version 5.5, specifically within the grab_image() function. This type of vulnerability falls under the Common Weakness Enumeration category CWE-918, which specifically addresses server-side request forgery conditions where an attacker can manipulate the application to make unintended requests to internal or external systems. The flaw exists in the content management system's image handling mechanism, where the grab_image() function fails to properly validate or sanitize user-supplied URLs that are used to fetch remote images for local storage.
The technical implementation of this vulnerability allows an attacker to provide malicious URLs to the grab_image() function, which then processes these requests on the server without adequate validation. This creates an environment where the vulnerable application can be coerced into making HTTP requests to internal network resources that would normally be protected by firewalls or network segmentation. The attacker can leverage this capability to enumerate internal services, access sensitive data, or potentially escalate privileges by targeting internal systems that are not directly exposed to the internet. The vulnerability is particularly dangerous because it can be exploited through various means including direct input manipulation or through other attack vectors that lead to the execution of the grab_image() function.
The operational impact of this vulnerability extends beyond simple data exfiltration, as it can enable attackers to perform reconnaissance activities against internal network infrastructure. According to ATT&CK framework category T1018, adversaries can use such vulnerabilities to discover and map internal network resources, potentially leading to further exploitation opportunities. The vulnerability could allow attackers to access internal services that are typically protected by network security controls, including database servers, administrative interfaces, or other sensitive systems. This capability significantly increases the attack surface for organizations using the affected CMS version, as it provides a potential entry point for lateral movement within the network.
Organizations utilizing YzmCMS v5.5 should immediately implement mitigations to address this vulnerability, including input validation and sanitization of all URLs passed to the grab_image() function. The recommended approach involves implementing strict URL validation that ensures only legitimate external domains are accepted, while blocking access to internal network addresses or private IP ranges. Additionally, network segmentation and firewall rules should be reviewed to minimize the potential impact of successful exploitation. The implementation of a proxy or gateway solution that can filter and validate all external requests made by the CMS would provide an additional layer of protection. Organizations should also consider implementing web application firewalls to detect and block suspicious requests that attempt to exploit this vulnerability. Regular security updates and patches should be applied to ensure the CMS remains protected against known vulnerabilities, with particular attention to the specific fix for CVE-2020-20341 that addresses the SSRF condition in the grab_image() function.