CVE-2014-6438 in Ruby
Summary
by MITRE
The URI.decode_www_form_component method in Ruby before 1.9.2-p330 allows remote attackers to cause a denial of service (catastrophic regular expression backtracking, resource consumption, or application crash) via a crafted string.
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Analysis
by VulDB Data Team • 06/03/2022
The vulnerability identified as CVE-2014-6438 represents a critical security flaw in Ruby's URI.decode_www_form_component method affecting versions prior to 1.9.2-p330. This issue manifests as a catastrophic regular expression backtracking vulnerability that can be exploited by remote attackers to execute denial of service attacks against applications relying on Ruby's URI handling capabilities. The flaw specifically targets the decoding mechanism used for processing URL-encoded components, making it particularly dangerous in web applications where user input is frequently processed through URI parsing functions.
The technical implementation of this vulnerability stems from the regular expression patterns used within Ruby's URI.decode_www_form_component method. When processing maliciously crafted input strings, these regular expressions exhibit exponential backtracking behavior, where the regex engine attempts multiple possible matches for the same input character, leading to exponential time complexity. This backtracking occurs when the input string contains specific patterns that cause the regular expression engine to explore numerous potential match combinations, ultimately consuming excessive CPU cycles and memory resources. The vulnerability is classified under CWE-1287, which specifically addresses catastrophic backtracking in regular expressions, and aligns with ATT&CK technique T1499.004 for resource consumption attacks.
The operational impact of CVE-2014-6438 extends beyond simple denial of service to potentially causing complete application crashes and system instability. Attackers can craft input strings that, when processed through URI.decode_www_form_component, trigger massive resource consumption that can exhaust server memory or CPU capacity. This makes the vulnerability particularly dangerous in high-traffic web applications or services where such resource exhaustion can lead to complete service disruption. The vulnerability affects any Ruby application that processes user-provided URI components, including web frameworks like Rails, Sinatra, and other applications that utilize Ruby's built-in URI parsing functionality.
Mitigation strategies for CVE-2014-6438 primarily focus on upgrading to Ruby versions that contain the patched implementation of URI.decode_www_form_component. Organizations should immediately upgrade to Ruby 1.9.2-p330 or later versions where the regular expression patterns have been optimized to prevent catastrophic backtracking. Additionally, input validation and sanitization measures should be implemented at application boundaries to filter out potentially malicious input before it reaches the URI parsing functions. Network-level protections such as rate limiting and input length restrictions can provide additional defense-in-depth measures, though these are secondary to the primary remediation of upgrading the Ruby runtime environment. The vulnerability demonstrates the critical importance of regular security updates and proper input validation in preventing exploitation of regex-based vulnerabilities that can lead to resource exhaustion and service disruption attacks.