CVE-2021-43838 in jsx-slack
Summary
by MITRE • 12/17/2021
jsx-slack is a library for building JSON objects for Slack Block Kit surfaces from JSX. In versions prior to 4.5.1 users are vulnerable to a regular expression denial-of-service (ReDoS) attack. If attacker can put a lot of JSX elements into `` tag, an internal regular expression for escaping characters may consume an excessive amount of computing resources. jsx-slack v4.5.1 has patched to a regex for escaping blockquote characters. Users are advised to upgrade as soon as possible.
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 12/24/2021
The jsx-slack library represents a critical vulnerability in the form of regular expression denial-of-service attack that affects versions prior to 4.5.1. This vulnerability stems from the library's handling of JSX elements within blockquote tags, where an internal regular expression used for character escaping becomes susceptible to malicious input patterns. The flaw specifically manifests when attackers can manipulate the content within the tag to trigger excessive computational resource consumption through poorly optimized regular expressions. This type of vulnerability falls under the common weakness enumeration CWE-400 which categorizes excessive computation vulnerabilities, and aligns with attack techniques described in the attack pattern taxonomy under the category of resource exhaustion attacks.
The technical implementation of this vulnerability occurs when the library processes JSX elements that contain specially crafted content within blockquote tags. The internal regular expression designed to escape characters becomes vulnerable to catastrophic backtracking scenarios where the regex engine spends exponential time trying to match malicious input patterns. This creates a situation where legitimate system resources become consumed disproportionately by the regular expression engine, effectively preventing normal operation of applications that depend on this library. The vulnerability is particularly concerning because it can be exploited through user-controlled input that flows through the JSX processing pipeline, making it accessible to attackers who can influence the content being processed.
The operational impact of CVE-2021-43838 extends beyond simple performance degradation to potentially complete system unavailability, especially in environments where the library handles high volumes of user input or where multiple concurrent requests can trigger the vulnerable regex patterns simultaneously. Applications using jsx-slack in production environments become susceptible to denial-of-service conditions that can be triggered by relatively simple malicious inputs, making this vulnerability particularly dangerous in web applications where user input is common. The vulnerability affects any system that processes Slack Block Kit surfaces through JSX syntax and could impact services ranging from chatbots to notification systems that rely on this library for content formatting.
Security mitigation for this vulnerability requires immediate upgrade to jsx-slack version 4.5.1 or later, which contains the patched regular expression for escaping blockquote characters. Organizations should conduct thorough vulnerability assessments to identify all systems using affected versions and implement proper input validation measures to prevent exploitation attempts. The fix implemented in version 4.5.1 addresses the specific regex pattern that was vulnerable to catastrophic backtracking, replacing it with a more efficient and secure pattern that cannot be exploited through malicious input sequences. System administrators should also consider implementing monitoring and alerting for unusual resource consumption patterns that might indicate exploitation attempts, while following best practices for secure coding and regular security updates to prevent similar vulnerabilities in other components of their software stack.