CVE-2013-6919 in phpThumb
Summary
by MITRE
The default configuration of phpThumb before 1.7.12 has a false value for the disable_debug option, which allows remote attackers to conduct Server-Side Request Forgery (SSRF) attacks via the src parameter.
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Analysis
by VulDB Data Team • 03/28/2019
The vulnerability identified as CVE-2013-6919 affects phpThumb versions prior to 1.7.12 and represents a critical security flaw in the default configuration that enables Server-Side Request Forgery attacks. This vulnerability specifically stems from a misconfiguration where the disable_debug option is set to a false value, creating an exploitable condition that allows remote attackers to manipulate the application's behavior. The phpThumb library serves as a PHP-based thumbnail generator that processes images from various sources, making it a common component in web applications that handle user-uploaded content or external image references. When the disable_debug parameter is enabled, it should prevent the application from making arbitrary HTTP requests to external resources, but due to the default false value, this protection mechanism fails.
The technical exploitation occurs through manipulation of the src parameter in the phpThumb application interface, where attackers can provide URLs that trigger the application to make HTTP requests to internal or external systems. This creates a pathway for attackers to perform reconnaissance activities, access internal network resources that should normally be protected from external access, or target other systems that are accessible from the server running phpThumb. The vulnerability allows for bypassing typical network segmentation controls and can be leveraged to probe internal network configurations, access sensitive resources, or even facilitate further attacks by establishing connections to other internal services. This type of vulnerability falls under the Common Weakness Enumeration category CWE-918, which specifically addresses Server-Side Request Forgery vulnerabilities where applications fail to properly validate or restrict external resource requests.
The operational impact of this vulnerability extends beyond simple information disclosure, as it enables attackers to potentially access internal systems that are not directly exposed to the internet. Attackers can use this vulnerability to perform network mapping activities, identify internal services, and potentially escalate their access by targeting other vulnerable systems within the same network segment. The vulnerability is particularly dangerous in environments where phpThumb is used in conjunction with other applications that may have weak security controls, as it can serve as a stepping stone for more comprehensive attacks. Additionally, the vulnerability can be exploited to access resources that might contain sensitive information or provide access to privileged systems. The attack vector is relatively simple and can be executed through standard web browser interactions, making it accessible to attackers with minimal technical expertise.
Mitigation strategies for CVE-2013-6919 primarily focus on updating to phpThumb version 1.7.12 or later, which contains the corrected configuration that properly disables the debug functionality. Organizations should also implement network-level controls such as firewall rules that restrict outbound connections from the server running phpThumb, particularly to internal network segments. The implementation of input validation and sanitization for the src parameter can further reduce the risk of exploitation, ensuring that only properly formatted URLs are accepted. Additionally, security monitoring should be implemented to detect unusual outbound network requests that might indicate exploitation attempts. According to the MITRE ATT&CK framework, this vulnerability aligns with techniques related to reconnaissance and initial access, specifically targeting the use of application vulnerabilities to gain unauthorized access to systems. Organizations should also consider implementing web application firewalls to provide additional layers of protection against such attacks, and conduct regular security assessments to identify and remediate similar configuration flaws in other applications. The vulnerability demonstrates the importance of proper default configurations and the critical need for security-conscious development practices where security controls are enabled by default rather than requiring manual configuration.