CVE-2011-4106 in TimThumb
Summary
by MITRE
TimThumb (timthumb.php) before 2.0 does not validate the entire source with the domain white list, which allows remote attackers to upload and execute arbitrary code via a URL containing a white-listed domain in the src parameter, then accessing it via a direct request to the file in the cache directory, as exploited in the wild in August 2011.
If you want to get best quality of vulnerability data, you may have to visit VulDB.
Analysis
by VulDB Data Team • 01/05/2025
The vulnerability described in CVE-2011-4106 represents a critical security flaw in the TimThumb library version 2.0 and earlier, which was widely exploited in the wild during August 2011. This vulnerability specifically targets the image processing and caching functionality of the library, which was commonly integrated into content management systems and web applications for dynamic image manipulation. The flaw stems from an inadequate validation mechanism that fails to properly verify the complete source URL against a predefined whitelist of allowed domains, creating a significant attack surface for malicious actors seeking to execute arbitrary code on vulnerable systems.
The technical implementation of this vulnerability relies on a fundamental flaw in input validation where the TimThumb script processes a source parameter containing a URL that includes a domain from the whitelisted domain list, but does not validate the complete URL structure. Attackers can exploit this by crafting a malicious URL that contains a legitimate domain from the whitelist as part of a longer URL, which the script accepts due to its incomplete validation approach. This allows the script to download and cache the malicious file, subsequently making it executable through direct requests to the cached file location. The vulnerability is classified under CWE-20, which addresses improper input validation, and represents a classic case of insecure direct object reference where the caching mechanism becomes a vector for code execution.
The operational impact of this vulnerability extends beyond simple code execution, as it provides attackers with persistent access to compromised systems through the cached files. The exploitation process typically involves uploading a malicious file through the vulnerable image processing endpoint, which then gets cached and made accessible through direct file requests. This creates a persistent backdoor that can be used for further compromise of the system, data exfiltration, or as a staging area for additional attacks. The vulnerability's widespread exploitation in 2011 demonstrates how a single input validation flaw in a popular library could affect thousands of websites and applications, highlighting the critical importance of proper security controls in widely-used components. Organizations using vulnerable versions of TimThumb were at risk of complete system compromise, as the cached files could contain malicious code that would execute with the privileges of the web server process.
The mitigation strategy for this vulnerability requires immediate patching of the TimThumb library to version 2.0 or later, which includes proper URL validation and domain checking mechanisms. System administrators should conduct comprehensive audits of their web applications to identify all instances of vulnerable TimThumb implementations and ensure they are updated. Additional security measures include implementing proper input validation at multiple layers, restricting file upload capabilities, and monitoring for suspicious file caching activities in web server directories. The vulnerability aligns with ATT&CK technique T1505.003, which covers 'Create or Modify System Process: Fileless Malware', as the exploitation creates persistent access points through cached files without requiring traditional file system modifications. Organizations should also consider implementing web application firewalls and content delivery network protections to prevent exploitation attempts and monitor for malicious URL patterns that could indicate attempts to leverage this vulnerability.