CVE-2021-33796 in MuJS
Summary
by MITRE • 07/07/2023
In MuJS before version 1.1.2, a use-after-free flaw in the regexp source property access may cause denial of service.
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 07/25/2023
The vulnerability CVE-2021-33796 represents a critical use-after-free flaw in the MuJS JavaScript engine version 1.1.1 and earlier. This vulnerability specifically affects the regular expression source property access mechanism within the engine's implementation. The flaw occurs when the engine processes regular expression objects and attempts to access their source property, creating a scenario where freed memory locations are accessed, leading to unpredictable behavior and potential system instability.
The technical implementation of this vulnerability stems from improper memory management within the MuJS engine's regular expression handling code. When a regular expression object is created and subsequently modified or destroyed, the engine fails to properly invalidate references to the source property before freeing the underlying memory. This creates a window where maliciously crafted JavaScript code can trigger the access of freed memory locations, resulting in memory corruption that manifests as denial of service conditions. The vulnerability operates at the intersection of memory safety and JavaScript engine implementation, making it particularly dangerous in environments where JavaScript engines are used for processing untrusted input.
The operational impact of this vulnerability extends beyond simple denial of service to potentially enable more sophisticated attack vectors. While the primary manifestation is denial of service, the use-after-free condition creates opportunities for memory corruption that could theoretically be exploited to execute arbitrary code. This vulnerability affects applications that rely on MuJS for JavaScript processing, particularly those in embedded systems, web applications, or any environment where JavaScript execution is delegated to the affected engine. The vulnerability is particularly concerning in server-side JavaScript environments where multiple concurrent requests could be affected, leading to cascading service disruptions and potential system compromise.
Mitigation strategies for CVE-2021-33796 primarily focus on immediate version upgrades to MuJS 1.1.2 or later, which contain the necessary memory management fixes. System administrators should prioritize patching affected systems and monitoring for potential exploitation attempts. Additionally, implementing input validation and sanitization measures can help reduce the attack surface by preventing malicious JavaScript code from reaching the vulnerable engine components. Organizations should also consider deploying intrusion detection systems that can identify patterns consistent with exploitation attempts targeting this specific vulnerability. The fix addresses the underlying CWE-416 use-after-free vulnerability pattern, which is categorized under the broader category of memory safety issues in software development practices. This vulnerability aligns with ATT&CK technique T1059.007 for JavaScript and T1499.004 for network denial of service, making it relevant to both application-level and infrastructure-level security monitoring efforts.