CVE-2010-1330 in JRuby
Summary
by MITRE
The regular expression engine in JRuby before 1.4.1, when $KCODE is set to u , does not properly handle characters immediately after a UTF-8 character, which allows remote attackers to conduct cross-site scripting (XSS) attacks via a crafted string.
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Analysis
by VulDB Data Team • 12/20/2021
The vulnerability identified as CVE-2010-1330 represents a critical security flaw within the JRuby regular expression engine that emerged in versions prior to 1.4.1. This issue specifically manifests when the $KCODE variable is configured to the 'u' setting, which enables UTF-8 character handling within the Ruby implementation. The flaw stems from improper processing of character sequences following UTF-8 multibyte characters, creating a pathway for malicious input to bypass security controls. The vulnerability operates at the intersection of character encoding handling and regular expression processing, where the engine fails to correctly interpret byte sequences that should be treated as single characters but instead processes them as separate entities.
The technical implementation of this vulnerability exploits the interaction between JRuby's Unicode handling mechanisms and its regular expression engine. When $KCODE is set to 'u', the system expects to process UTF-8 encoded strings with proper character boundaries, but the regex engine fails to correctly identify where one UTF-8 character ends and another begins. This misinterpretation allows attackers to craft strings where certain byte sequences that should be treated as single UTF-8 characters are instead processed as individual bytes, enabling the insertion of malicious content that can bypass XSS filters. The flaw specifically affects the handling of characters immediately following UTF-8 multibyte sequences, creating a window where attacker-controlled input can be interpreted in unexpected ways.
The operational impact of this vulnerability extends significantly in web application environments where JRuby is used for processing user input and implementing security controls. Remote attackers can leverage this weakness to inject malicious scripts that would normally be blocked by XSS protection mechanisms, as the flawed character processing allows malicious payloads to be concealed within UTF-8 encoded strings. The vulnerability directly maps to CWE-79, which describes Cross-Site Scripting vulnerabilities, and aligns with ATT&CK technique T1059.007 for Scripting, where attackers exploit application-level scripting vulnerabilities. Applications using JRuby with UTF-8 character handling are particularly at risk, as the vulnerability can be exploited to execute arbitrary JavaScript code in victim browsers, potentially leading to session hijacking, data theft, or further compromise of affected systems.
Mitigation strategies for CVE-2010-1330 require immediate patching of JRuby installations to version 1.4.1 or later, where the regular expression engine properly handles UTF-8 character boundaries. Organizations should also implement input validation and sanitization measures that do not rely solely on regular expression-based XSS filtering, particularly when dealing with UTF-8 encoded content. Security teams should review application code to identify instances where $KCODE is set to 'u' and evaluate whether this setting is necessary for application functionality. Additionally, network-based intrusion detection systems should be configured to monitor for suspicious UTF-8 encoded payloads that might indicate exploitation attempts. The fix implemented in JRuby 1.4.1 addresses the core issue by ensuring proper UTF-8 character boundary detection in regular expression processing, preventing the character interpretation anomalies that enabled the XSS attack vectors.