CVE-2023-36617 in Ruby
Summary
by MITRE • 06/29/2023
A ReDoS issue was discovered in the URI component before 0.12.2 for Ruby. The URI parser mishandles invalid URLs that have specific characters. There is an increase in execution time for parsing strings to URI objects with rfc2396_parser.rb and rfc3986_parser.rb. NOTE: this issue exists becuse of an incomplete fix for CVE-2023-28755. Version 0.10.3 is also a fixed version.
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Analysis
by VulDB Data Team • 07/17/2025
The vulnerability CVE-2023-36617 represents a Regular Expression Denial of Service (ReDoS) flaw in Ruby's URI component library, specifically affecting versions prior to 0.12.2. This issue arises from the improper handling of malformed URLs containing specific character sequences that cause the URI parser to enter into exponential time complexity during string parsing operations. The vulnerability is particularly concerning because it demonstrates how incomplete security fixes can create new attack vectors, as this issue emerged due to an inadequate resolution of a previously reported vulnerability CVE-2023-28755. The affected parsers rfc2396_parser.rb and rfc3986_parser.rb exhibit dramatically increased execution times when processing maliciously crafted input strings, making them susceptible to resource exhaustion attacks that can effectively disable applications relying on URI parsing functionality. This vulnerability falls under the Common Weakness Enumeration category CWE-400, which specifically addresses Uncontrolled Resource Consumption, and aligns with the ATT&CK technique T1496 for Resource Hijacking, as attackers can exploit this weakness to consume excessive computational resources.
The technical implementation of this vulnerability stems from regular expression patterns within the URI parsing logic that are susceptible to catastrophic backtracking when confronted with carefully constructed input. When the URI parser encounters malformed URLs containing specific character combinations, particularly those that trigger nested quantifiers in the regular expressions, the parsing algorithm experiences exponential time growth, where the execution time increases dramatically with input length. This occurs because the regular expression engine must backtrack through multiple possible matches before determining the correct parsing path, leading to potential system hangs or denial of service conditions. The impact is particularly severe in web applications that process user-supplied URLs or in systems that parse large volumes of URI data, where a single malicious input can cause significant performance degradation or complete service unavailability. The vulnerability affects Ruby applications that utilize the uri gem for URL parsing, including web frameworks, API clients, and any software components that depend on proper URI handling for network communication or data processing operations.
The operational impact of CVE-2023-36617 extends beyond simple performance degradation to potentially compromise entire application availability and system stability. Attackers can exploit this vulnerability by submitting maliciously crafted URLs that trigger the exponential parsing time, causing applications to become unresponsive or consume excessive CPU resources. This makes the vulnerability particularly dangerous in high-traffic environments or applications where URI parsing is frequently performed, such as web servers processing user requests, API gateways, or content management systems. The vulnerability also represents a regression issue, as it indicates that security fixes for related vulnerabilities were incomplete or insufficient, potentially leaving systems vulnerable to similar attacks even after applying what appeared to be corrective measures. Organizations running Ruby applications with affected uri gem versions face significant risk of service disruption, as this vulnerability can be exploited through various attack vectors including web forms, API endpoints, or any input mechanism that processes user-supplied URLs. The fix requires updating to version 0.12.2 or 0.10.3, which contain proper regular expression handling that prevents catastrophic backtracking scenarios.
Mitigation strategies for CVE-2023-36617 primarily involve immediate version upgrades of the uri gem to 0.12.2 or 0.10.3, which contain the corrected regular expression patterns that eliminate the catastrophic backtracking behavior. Organizations should conduct comprehensive testing of their applications after applying the updates to ensure that the fix does not introduce any compatibility issues or regressions in URI parsing functionality. Additionally, implementing input validation and sanitization measures can provide defense-in-depth protection, where applications should reject or properly escape suspicious URL patterns before they reach the URI parser. Network-level protections such as rate limiting and request timeouts can also help mitigate the impact of potential attacks by preventing excessive resource consumption from single requests. Security monitoring should include detection of unusual URI parsing patterns or sustained high CPU usage that might indicate exploitation attempts. The vulnerability serves as a reminder of the importance of thorough security testing and validation of fixes, particularly when addressing related vulnerabilities, as incomplete remediations can leave systems vulnerable to similar attack patterns. System administrators should also consider implementing automated vulnerability scanning tools that can detect the presence of affected uri gem versions in their application environments to ensure comprehensive protection against this and related ReDoS vulnerabilities.