CVE-2009-3493 in PaoBacheca Guestbook
Summary
by MITRE
Multiple cross-site scripting (XSS) vulnerabilities in Zenas PaoBacheca Guestbook 2.1 allow remote attackers to inject arbitrary web script or HTML via the PATH_INFO to (1) scrivi.php and (2) index.php.
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Analysis
by VulDB Data Team • 07/28/2025
The vulnerability identified as CVE-2009-3493 affects Zenas PaoBacheca Guestbook version 2.1 and represents a critical cross-site scripting flaw that enables remote attackers to execute malicious scripts within the context of victim browsers. This vulnerability specifically exploits improper input validation mechanisms within the application's handling of PATH_INFO parameters, which are typically used to pass additional information to web scripts through the URL path. The flaw exists in two primary files: scrivi.php and index.php, making it particularly dangerous as it affects core guestbook functionality where user interactions are expected to be safe.
The technical implementation of this vulnerability stems from the application's failure to properly sanitize or escape user-supplied input that flows directly into HTML output without adequate security controls. When attackers craft malicious payloads and inject them through the PATH_INFO parameter, the web application processes these inputs without sufficient validation, allowing the malicious code to be executed in the victim's browser context. This type of vulnerability falls under CWE-79 which specifically addresses Cross-Site Scripting vulnerabilities in software applications, where improper handling of untrusted data leads to arbitrary code execution within the victim's browser environment.
The operational impact of this vulnerability extends beyond simple script injection, as it provides attackers with the capability to perform session hijacking, defacement of guestbook entries, and potentially more severe attacks such as credential theft or redirection to malicious sites. Since guestbooks typically serve as public-facing interfaces where users can submit comments and entries, the attack surface is broad and easily exploitable. Attackers can craft malicious URLs that, when clicked by unsuspecting users, would execute their payloads in the user's browser context, effectively turning the guestbook into a vector for spreading malicious content across the entire user base.
The exploitation of this vulnerability aligns with ATT&CK technique T1566 which covers spearphishing through social engineering attacks, where the XSS payload can be embedded within guestbook entries or comments to lure users into executing malicious code. Organizations using this vulnerable software face significant risk of reputational damage, user data compromise, and potential regulatory compliance violations. The vulnerability's persistence in the application's core functionality means that even legitimate users could inadvertently expose themselves to attacks through normal usage patterns.
Mitigation strategies for this vulnerability include immediate implementation of input validation and output encoding mechanisms, particularly for PATH_INFO parameters and any user-supplied data that flows into HTML contexts. The application should employ proper HTML escaping routines before displaying any user-provided content, and implement Content Security Policy headers to limit script execution capabilities. Additionally, regular security audits and input validation testing should be conducted to identify similar vulnerabilities in other application components. The fix requires developers to ensure that all user inputs are properly sanitized and that the application follows secure coding practices as outlined in OWASP Top Ten and other industry security standards, with particular attention to preventing XSS vulnerabilities through proper input validation and output encoding techniques.