CVE-2020-5219 in Angular Expressions
Summary
by MITRE
Angular Expressions before version 1.0.1 has a remote code execution vulnerability if you call expressions.compile(userControlledInput) where userControlledInput is text that comes from user input. If running angular-expressions in the browser, an attacker could run any browser script when the application code calls expressions.compile(userControlledInput). If running angular-expressions on the server, an attacker could run any Javascript expression, thus gaining Remote Code Execution.
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Analysis
by VulDB Data Team • 03/26/2024
The vulnerability identified as CVE-2020-5219 represents a critical remote code execution flaw within the angular-expressions library, specifically affecting versions prior to 1.0.1. This vulnerability stems from improper input validation and sanitization mechanisms within the expressions.compile() function, which processes user-controlled input without adequate security measures. The flaw exists at the intersection of web application security and server-side code execution, creating a dangerous attack surface where malicious actors can manipulate application behavior through crafted input sequences. The vulnerability is particularly concerning because it operates at the expression parsing level, allowing attackers to inject arbitrary code that executes within the application context, whether in browser or server environments. The root cause aligns with CWE-94, which describes weaknesses in the code that allow arbitrary code execution, specifically manifesting as insufficient input validation and improper handling of user-supplied data.
The technical implementation of this vulnerability occurs when applications utilize the expressions.compile() method with user-provided input, creating a direct pathway for code injection attacks. In browser environments, the vulnerability enables attackers to execute arbitrary JavaScript code within the victim's browser context, potentially leading to session hijacking, data theft, or malicious payload delivery through techniques such as cross-site scripting. When the library operates on the server side, the implications become even more severe as attackers can execute arbitrary JavaScript expressions, effectively gaining full control over the server execution environment. This dual nature of the vulnerability makes it particularly dangerous as it can be exploited in both client-side and server-side contexts, depending on how the library is integrated into the application architecture. The attack vector typically involves crafting malicious input that bypasses normal expression parsing and gets executed as legitimate code, exploiting the lack of proper sanitization mechanisms.
The operational impact of CVE-2020-5219 extends beyond immediate code execution capabilities to encompass broader security implications for applications relying on angular-expressions. Organizations using affected versions face significant risks including data breaches, unauthorized access to sensitive systems, and potential compromise of entire application infrastructures. The vulnerability can be exploited through various attack scenarios including web application penetration testing, social engineering campaigns, or automated scanning tools that identify vulnerable endpoints. In enterprise environments, this vulnerability can lead to cascading security failures as attackers may use the initial compromise to pivot to other systems within the network. The impact is further amplified by the fact that many applications may not immediately detect or alert on such code execution events, making the vulnerability particularly stealthy and difficult to detect during routine security monitoring.
Mitigation strategies for CVE-2020-5219 require immediate version updates to angular-expressions 1.0.1 or later, which include proper input sanitization and validation mechanisms. Organizations should implement comprehensive input validation at all application layers, ensuring that user-controlled data undergoes strict sanitization before being processed by expression parsing functions. The implementation of Content Security Policy headers can provide additional protection against code injection attacks by restricting script execution within browser environments. Security teams should also conduct thorough code reviews focusing on expression parsing functions and user input handling, particularly in areas where external data is processed. Additionally, implementing proper application monitoring and logging mechanisms can help detect anomalous expression execution patterns that may indicate exploitation attempts. Organizations should consider adopting the principle of least privilege for expression execution contexts and implement proper sandboxing mechanisms when processing untrusted input. The remediation process should also include updating related dependencies and conducting security assessments to identify other potential vulnerabilities within the application stack that may be similarly affected by improper input handling practices.