CVE-2015-5594 in ZenPhoto
Summary
by MITRE
The sanitize_string function in ZenPhoto before 1.4.9 utilized the html_entity_decode function after input sanitation, which might allow remote attackers to perform a cross-site scripting (XSS) via a crafted string.
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Analysis
by VulDB Data Team • 03/31/2025
The vulnerability identified as CVE-2015-5594 resides within the ZenPhoto content management system prior to version 1.4.9, specifically within the sanitize_string function that handles input validation and sanitization processes. This flaw represents a classic case of improper input handling where the sequence of operations creates an exploitable condition that undermines the intended security protections. The vulnerability manifests when user-supplied input undergoes sanitization followed by html_entity_decode processing, creating a pathway for malicious actors to inject persistent cross-site scripting payloads that can execute within the context of other users' browsers.
The technical implementation of this vulnerability stems from a fundamental flaw in the order of operations within the input sanitization pipeline. When the sanitize_string function processes user input, it first applies sanitization measures to remove or neutralize potentially dangerous characters and sequences, but subsequently invokes html_entity_decode on the sanitized data. This reversal of the sanitization process effectively reverts the encoded entities back to their original form, thereby reintroducing the malicious payloads that were previously neutralized. The vulnerability falls under CWE-79 Improper Neutralization of Input During Web Page Generation, specifically manifesting as a case where the application fails to properly neutralize user input before it is rendered in web pages, creating an XSS vector that can be exploited by remote attackers without requiring authentication or specific privileges.
The operational impact of CVE-2015-5594 extends beyond simple data theft or defacement, as it enables attackers to execute arbitrary JavaScript code within the context of affected users' browsers. This capability allows for session hijacking, credential theft, redirection to malicious sites, and the potential for privilege escalation within the application. The vulnerability is particularly concerning because it operates silently in the background, allowing attackers to inject malicious scripts that can persist across multiple user sessions and potentially compromise the entire application environment. Attackers can craft payloads that exploit this vulnerability by submitting specially crafted strings containing encoded HTML entities that, when processed through the flawed sanitization sequence, result in executable JavaScript code within the victim's browser context.
From a threat modeling perspective, this vulnerability aligns with ATT&CK technique T1059.007 Command and Scripting Interpreter: JavaScript, where attackers leverage the XSS capability to execute malicious JavaScript code. The vulnerability also maps to ATT&CK tactic TA0001 Initial Access, as it provides an entry point for attackers to establish a foothold within the target environment. Security professionals should note that this vulnerability demonstrates the critical importance of maintaining consistent input sanitization practices and avoiding operations that reverse sanitization processes. The flaw represents a common anti-pattern in web application security where developers assume that certain functions will automatically neutralize threats, without considering the sequence and interaction between multiple security controls.
Mitigation strategies for CVE-2015-5594 require immediate implementation of the vendor-provided patch that updates ZenPhoto to version 1.4.9 or later, which corrects the flawed sanitization sequence. Organizations should also implement comprehensive input validation at multiple layers of their applications, ensuring that no sanitization operations are followed by decoding functions that could reintroduce threats. Additional defensive measures include implementing Content Security Policy headers, utilizing proper output encoding for all dynamic content, and conducting regular security code reviews to identify similar anti-patterns. The vulnerability serves as a critical reminder of the importance of following established security principles such as the principle of least privilege and defense in depth, where multiple security controls work together to protect against various attack vectors rather than relying on a single line of defense.