CVE-2020-26303 in insane
Summary
by MITRE • 10/26/2024
insane is a whitelist-oriented HTML sanitizer. Versions 2.6.2 and prior contain one or more regular expressions that are vulnerable to Regular Expression Denial of Service (ReDoS). As of time of publication, no known patches are available.
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Analysis
by VulDB Data Team • 11/14/2024
The CVE-2020-26303 vulnerability affects insane, a whitelist-oriented HTML sanitizer library that processes and sanitizes HTML content to prevent cross-site scripting attacks and other malicious input. This particular vulnerability resides within the regular expression patterns used by the sanitizer to validate and filter HTML elements and attributes. The issue manifests as a Regular Expression Denial of Service (ReDoS) vulnerability, which occurs when an attacker crafts malicious input that causes the regular expression engine to consume excessive computational resources during pattern matching operations.
The technical flaw stems from poorly constructed regular expressions within the insane library's validation logic that are susceptible to catastrophic backtracking. When processing specially crafted HTML input, these regular expressions can cause the JavaScript engine to spend an exponentially increasing amount of time trying to match patterns, ultimately leading to service unavailability. This vulnerability operates at the application level and can be exploited by attackers who can influence the HTML content processed by the sanitizer, making it particularly dangerous in web applications that accept user-generated content.
The operational impact of this vulnerability is significant as it can be leveraged to perform denial of service attacks against applications that rely on insane for HTML sanitization. Attackers can craft malicious HTML payloads that, when processed by the vulnerable sanitizer, cause the application to become unresponsive or crash, effectively denying service to legitimate users. The vulnerability affects all versions up to and including 2.6.2, and since no patches were available at the time of publication, affected applications remained exposed to this threat. This type of vulnerability directly maps to CWE-400, which specifically addresses unchecked resource consumption, and aligns with ATT&CK technique T1499.004 for network denial of service attacks.
Organizations utilizing insane in their applications should immediately implement defensive measures including input validation and sanitization at multiple layers, rate limiting of HTML processing requests, and monitoring for unusual processing times that may indicate exploitation attempts. Additionally, the use of alternative HTML sanitization libraries that have been audited for ReDoS vulnerabilities should be considered as a long-term solution. The vulnerability highlights the critical importance of regular security auditing of third-party libraries and the need for comprehensive testing of regular expression patterns used in security-critical applications. Security teams should also consider implementing intrusion detection systems that can identify patterns consistent with ReDoS attacks and establish incident response procedures for handling such vulnerabilities in production environments.