CVE-2007-3295 in YaBB
Summary
by MITRE
Directory traversal vulnerability in Yet another Bulletin Board (YaBB) 2.1 and earlier allows remote authenticated users to execute arbitrary Perl code via a .. (dot dot) in the userlanguage profile setting, which sets the userlanguage key of the member hash, and is propagated to the language variable in (1) HelpCentre.pl and (2) ICQPager.pl, (3) the use_lang variable in Subs.pl, and the actlang variable in (4) Post.pl and (5) InstantMessage.pl; as demonstrated by pointing userlanguage to the English folder, modifying English/HelpCentre.lng file to contain Perl statements, and then invoking the help action in YaBB.pl.
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Analysis
by VulDB Data Team • 04/23/2018
The vulnerability described in CVE-2007-3295 represents a critical directory traversal flaw within the Yet another Bulletin Board (YaBB) version 2.1 and earlier systems. This security weakness exists in the userlanguage profile setting mechanism that handles user language preferences within the bulletin board system. The flaw allows authenticated remote attackers to manipulate the system by exploiting how the userlanguage parameter is processed and propagated throughout multiple Perl script files within the YaBB framework. The vulnerability specifically manifests when the userlanguage parameter contains directory traversal sequences such as .. (dot dot) characters that can navigate outside the intended directory structure.
The technical implementation of this vulnerability involves the manipulation of the userlanguage key within the member hash structure, which then gets assigned to various language-related variables across multiple script files. The propagation occurs through specific Perl scripts including HelpCentre.pl, ICQPager.pl, Subs.pl, Post.pl, and InstantMessage.pl where the language variable is utilized. The vulnerability is particularly dangerous because it allows attackers to modify the language files that are loaded by these scripts, specifically targeting the English/HelpCentre.lng file in the demonstration case. When an attacker modifies this language file to contain malicious Perl statements, the system executes these statements during normal operation when the help action is invoked through YaBB.pl, effectively enabling remote code execution.
This vulnerability has significant operational impact as it transforms a simple user preference setting into a potential gateway for complete system compromise. The attack requires only authenticated access to the system, which is often readily available through legitimate user accounts, making the exploitation more feasible than many other remote code execution vulnerabilities. The directory traversal mechanism allows attackers to access and modify files outside the intended language directory structure, potentially enabling access to system configuration files, database connection details, or other sensitive components. The exploitation chain demonstrates how seemingly benign user input handling can become a critical security flaw when proper sanitization and validation are not implemented.
The vulnerability aligns with CWE-22 Directory Traversal and CWE-94 Code Injection categories, representing a classic example of how improper input validation can lead to arbitrary code execution. From an adversarial perspective, this vulnerability maps to ATT&CK technique T1059.006 for execution through Perl scripting and T1021.004 for remote service access. Organizations running YaBB 2.1 or earlier versions face substantial risk of unauthorized code execution, data theft, and potential complete system compromise. The vulnerability demonstrates the importance of input validation and proper file access controls in web applications, particularly in systems that dynamically include or load files based on user input parameters. The attack vector emphasizes the need for secure coding practices in handling user-supplied data that influences system behavior and file operations.
Mitigation strategies should focus on implementing proper input validation and sanitization of the userlanguage parameter to prevent directory traversal sequences from being processed. The system should enforce strict file access controls that prevent modification of critical system files and implement proper path validation to ensure that user input cannot navigate outside designated directories. Additionally, the affected YaBB versions should be upgraded to patched releases that address this vulnerability, as the original codebase contains fundamental flaws in how user preferences are handled and propagated throughout the application. Organizations should also consider implementing web application firewalls and monitoring for suspicious directory traversal patterns in their network traffic to detect potential exploitation attempts.