CVE-2011-5081 in BackupPC
Summary
by MITRE
Cross-site scripting (XSS) vulnerability in RestoreFile.pm in BackupPC 3.1.0, 3.2.1, and possibly other earlier versions allows remote attackers to inject arbitrary web script or HTML via the share parameter in a RestoreFile action to index.cgi.
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Analysis
by VulDB Data Team • 09/08/2025
The CVE-2011-5081 vulnerability represents a critical cross-site scripting flaw in BackupPC's RestoreFile functionality, specifically within the RestoreFile.pm module. This vulnerability affects versions 3.1.0 and 3.2.1 of the BackupPC backup solution, making it a significant concern for organizations relying on this backup management system. The flaw stems from inadequate input validation and sanitization within the web interface, creating an avenue for malicious actors to execute arbitrary code in the context of affected users' browsers.
The technical exploitation occurs through manipulation of the share parameter in the RestoreFile action of index.cgi, which serves as the primary attack vector for this XSS vulnerability. When a user accesses the vulnerable restore functionality with a maliciously crafted share parameter, the application fails to properly sanitize user input before incorporating it into the web response. This processing flaw allows attackers to inject malicious scripts that execute in the victim's browser session, potentially leading to session hijacking, credential theft, or further exploitation of the compromised system.
From an operational impact perspective, this vulnerability poses substantial risks to backup infrastructure security, particularly in enterprise environments where BackupPC is deployed for managing critical data backups. The remote nature of the attack means that adversaries can exploit this flaw without requiring local system access or authentication, making it particularly dangerous. Successful exploitation could enable attackers to access backup configurations, view sensitive backup data, or manipulate the backup process itself, potentially leading to data corruption or unauthorized access to backup repositories.
The vulnerability aligns with CWE-79, which specifically addresses cross-site scripting flaws in web applications, and demonstrates poor input validation practices that violate fundamental secure coding principles. According to ATT&CK framework, this vulnerability maps to T1566.001 (Phishing: Spearphishing Attachment) and T1059.007 (Command and Scripting Interpreter: JavaScript), as attackers could leverage this flaw to deliver malicious JavaScript payloads. Organizations should implement immediate mitigations including applying the vendor-provided patches, implementing input validation at the application level, and deploying web application firewalls to detect and block malicious payloads targeting this specific vulnerability.
The remediation strategy should include comprehensive patch management to upgrade to versions of BackupPC that address this vulnerability, along with implementing proper input sanitization and output encoding for all user-supplied parameters. Security teams should also consider network-level protections such as web application firewalls and content security policies to provide defense-in-depth against similar XSS vulnerabilities. Regular security assessments of backup management systems are essential to identify and remediate similar flaws that could compromise backup integrity and data security.