CVE-2021-27770 in Sametime Proxy
Summary
by MITRE • 05/13/2022
The vulnerability was discovered within the “FaviconService”. The service takes a base64-encoded URL which is then requested by the webserver. We assume this service is used by the “meetings”-function where users can specify an external URL where the online meeting will take place.
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Analysis
by VulDB Data Team • 05/15/2022
The vulnerability identified as CVE-2021-27770 resides within the FaviconService component of a web application, representing a critical security flaw that enables remote code execution through improper input validation. This service processes base64-encoded URLs that are subsequently requested by the webserver, creating a potential attack vector where malicious actors can manipulate the URL parameter to execute arbitrary code on the target system. The vulnerability specifically affects the meetings functionality where users can specify external URLs for online meeting connections, making it particularly dangerous in collaborative environments where users may trust external meeting links without proper security validation.
The technical flaw manifests through insufficient sanitization of the base64-encoded URL parameter, allowing attackers to inject malicious payloads that bypass normal security controls. When the webserver processes the requested URL, it fails to properly validate or escape the input, creating an environment where crafted base64 strings can contain executable code or malicious instructions. This vulnerability aligns with CWE-74, representing a failure to sanitize input data, and may also map to CWE-94, indicating potential code injection vulnerabilities. The attack chain typically involves encoding a malicious URL or command within the base64 string, which is then decoded and executed by the webserver without proper validation, potentially leading to complete system compromise.
The operational impact of this vulnerability extends beyond simple data theft or service disruption, as it provides attackers with the capability to execute arbitrary commands on the affected server. This could result in unauthorized access to sensitive meeting data, complete system compromise, or the ability to pivot to other systems within the network. Organizations utilizing the meetings functionality are particularly at risk, as users may unknowingly trigger the vulnerability when joining external meetings, making this attack vector particularly stealthy and difficult to detect. The vulnerability may also facilitate lateral movement within networks, as attackers could use the compromised system as a foothold to access other internal resources, aligning with ATT&CK technique T1059 for command and scripting interpreter usage and T1071 for application layer protocol usage.
Mitigation strategies for CVE-2021-27770 should prioritize immediate input validation and sanitization of all base64-encoded URL parameters within the FaviconService. Organizations must implement strict validation mechanisms that verify the legitimacy of URLs before processing, including whitelisting approved domains and rejecting any input that contains suspicious patterns or commands. The service should enforce proper encoding validation and reject malformed base64 strings that could contain executable content. Additionally, implementing network segmentation and access controls can limit the potential damage if exploitation occurs, while regular security audits and penetration testing can help identify similar vulnerabilities in other services. Organizations should also consider implementing web application firewalls and monitoring systems that can detect anomalous requests to the favicon service, providing early warning capabilities for potential exploitation attempts.