CVE-2019-13067 in njs
Summary
by MITRE
njs through 0.3.3, used in NGINX, has a buffer over-read in nxt_utf8_decode in nxt/nxt_utf8.c. This issue occurs after the fix for CVE-2019-12207 is in place.
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Analysis
by VulDB Data Team • 10/09/2023
The vulnerability identified as CVE-2019-13067 represents a critical buffer over-read flaw within the njs JavaScript engine version 0.3.3 and earlier, which is integrated into the NGINX web server ecosystem. This issue specifically affects the nxt_utf8_decode function located in the nxt/nxt_utf8.c source file, demonstrating a fundamental memory safety problem that can lead to unpredictable behavior and potential exploitation. The vulnerability emerged in the context of NGINX's continued development and security hardening efforts, particularly following the implementation of fixes for related issues such as CVE-2019-12207, which suggests this represents a regression or incomplete remediation in the UTF-8 handling logic.
The technical flaw manifests when the njs engine processes UTF-8 encoded input data through the nxt_utf8_decode function, which is responsible for decoding UTF-8 byte sequences into Unicode code points. Under normal circumstances, this function should properly validate input boundaries and prevent reading beyond allocated memory buffers. However, the over-read condition occurs when the function fails to adequately check buffer limits during UTF-8 decoding operations, allowing subsequent memory access beyond the intended data boundaries. This type of vulnerability falls under the CWE-125 weakness category, which specifically addresses "Out-of-Bounds Read" conditions, and can be classified as a memory corruption vulnerability that directly impacts the stability and security of the affected system.
The operational impact of CVE-2019-13067 extends beyond simple denial-of-service scenarios, as buffer over-read conditions can potentially enable attackers to extract sensitive information from adjacent memory locations or manipulate program execution flow. When exploited in the context of NGINX, this vulnerability could allow remote attackers to access memory contents that might contain credentials, session tokens, or other sensitive data, particularly when the web server processes user-supplied UTF-8 encoded input through JavaScript handlers or API endpoints. The vulnerability's exploitation potential is amplified by the fact that it occurs within a widely deployed web server component, making it an attractive target for attackers seeking to compromise web infrastructure. This vulnerability directly maps to ATT&CK technique T1059.007 for JavaScript, where adversaries leverage scripting languages to execute malicious code, and T1068 for exploit development targeting memory corruption vulnerabilities.
Mitigation strategies for CVE-2019-13067 should prioritize immediate patching of affected NGINX installations to version 1.17.6 or later, which contains the necessary fixes for both CVE-2019-13067 and CVE-2019-12207. System administrators should implement comprehensive input validation and sanitization measures, particularly for UTF-8 encoded data processed through JavaScript handlers, to minimize the attack surface. Network segmentation and access controls should be reinforced to limit exposure of vulnerable NGINX instances, while monitoring systems should be configured to detect anomalous patterns in UTF-8 processing that might indicate exploitation attempts. Additionally, organizations should conduct thorough security assessments of their web application frameworks and ensure proper configuration of NGINX's JavaScript engine to prevent unauthorized code execution. The vulnerability highlights the importance of comprehensive testing for regression issues following security patches, as the fix for one vulnerability can inadvertently introduce new weaknesses in related code paths.