CVE-2020-8159 in actionpack_page-caching Gem
Summary
by MITRE
There is a vulnerability in actionpack_page-caching gem < v1.2.1 that allows an attacker to write arbitrary files to a web server, potentially resulting in remote code execution if the attacker can write unescaped ERB to a view.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 05/13/2020
The vulnerability identified as CVE-2020-8159 resides within the actionpack_page-caching gem version 1.2.0 and earlier, representing a critical security flaw that enables attackers to achieve arbitrary file writing capabilities on affected web servers. This vulnerability specifically targets applications utilizing the Rails framework that employ page caching functionality, creating a significant attack surface that can be exploited to compromise server integrity and potentially execute malicious code remotely. The flaw stems from inadequate input validation and sanitization mechanisms within the page caching implementation, allowing malicious actors to manipulate file paths and content through crafted requests.
The technical nature of this vulnerability falls under CWE-73, which describes "External Control of File Name or Path" - a weakness where an application uses external input to construct file paths without proper validation, leading to unauthorized file system access. The vulnerability manifests when the actionpack_page-caching gem processes user-supplied data that gets directly incorporated into file system operations, particularly when rendering cached pages. Attackers can exploit this by crafting specific requests that include malicious file paths or content, enabling them to write arbitrary files to the web server's file system. The severity escalates when the attacker can inject unescaped erb code into view files, as this creates opportunities for remote code execution through the web server's ability to process and execute ruby code within cached templates.
The operational impact of CVE-2020-8159 extends beyond simple file system compromise, as it provides attackers with potential persistence mechanisms and escalation opportunities within affected environments. When combined with the ability to write unescaped ERB content, attackers can create backdoor files that execute arbitrary commands on the server, effectively granting them full control over the affected web application and potentially the underlying infrastructure. This vulnerability affects organizations running Rails applications with page caching enabled, particularly those that have not updated to version 1.2.1 or later, making it a widespread concern across many production environments. The attack vector typically involves sending specially crafted HTTP requests that bypass normal validation checks, allowing the malicious input to be processed through the vulnerable caching mechanism.
Mitigation strategies for this vulnerability require immediate patching of the actionpack_page-caching gem to version 1.2.1 or later, which includes proper input validation and sanitization measures to prevent malicious file path manipulation. Organizations should also implement comprehensive monitoring of file system changes on affected servers to detect unauthorized file creations, particularly in directories where web application content is stored. Network-level defenses such as web application firewalls can help detect and block malicious requests attempting to exploit this vulnerability, though the most effective defense remains timely patch management. Additionally, security teams should conduct thorough audits of all Rails applications to identify those utilizing page caching functionality and ensure proper input validation is implemented at all levels of the application stack. The ATT&CK framework categorizes this vulnerability under T1059.007 "Command and Scripting Interpreter: Python" and T1078.004 "Valid Accounts: Cloud Accounts" when considering the potential for privilege escalation and persistent access through the exploited server. Organizations should also consider implementing principle of least privilege access controls and regular security assessments to prevent exploitation of similar vulnerabilities in their web application infrastructure.