CVE-2020-9038 (joplin)

CVE-2020-9038: A XSS Vulnerability in Joplin

Joplin is a popular open source note-taking and to-do application that supports multiple platforms and synchronization. However, it was discovered that Joplin through version 1.0.184 had a cross-site scripting (XSS) vulnerability that could allow an attacker to read arbitrary files from the victim's device.

The vulnerability was reported by 0x240x23elu on GitHub on February 18, 2020. According to the report, the vulnerability existed in the markdown editor component of Joplin, which did not properly sanitize user input. An attacker could craft a malicious note with embedded JavaScript code and share it with the victim via Joplin's synchronization feature. When the victim opened the note in Joplin, the JavaScript code would execute and access the victim's file system via the Node.js fs module.

The vulnerability was assigned the identifier CVE-2020-9038 by NIST and given a base score of 5.4 (medium severity) on the CVSS v3 scale[^1^]. The vulnerability affected Joplin versions up to and including 1.0.184 on Windows, Linux, macOS, Android and iOS platforms. The vulnerability was fixed in Joplin version 1.0.185, which was released on February 19, 2020. Users of Joplin are advised to update to the latest version as soon as possible to prevent potential attacks.

How to prevent XSS attacks

XSS attacks can be prevented by applying proper input validation and output encoding techniques. Input validation means checking that the user input does not contain any malicious code or characters that could be interpreted as code by the browser. Output encoding means transforming the user input into a safe format that cannot be executed as code by the browser. For example, HTML entities can be used to encode special characters like , and &.

There are different types of output encoding depending on the context where the user input is displayed. For example, HTML encoding should be used for HTML attributes and content, URL encoding should be used for URL parameters and query strings, and JavaScript encoding should be used for JavaScript code. Using the wrong type of encoding or no encoding at all can lead to XSS vulnerabilities.

Some web frameworks and libraries provide built-in functions or components to perform input validation and output encoding automatically. However, developers should be aware of the limitations and exceptions of these functions or components, and use them correctly and consistently throughout the application. For example, React's dangerouslySetInnerHTML prop should be avoided or used with caution, as it allows raw HTML to be rendered without escaping.

In addition to input validation and output encoding, other techniques can help mitigate XSS attacks, such as using Content Security Policy (CSP) headers to restrict the sources of scripts and other resources that can be loaded by the browser, using HTTP-only and secure cookies to protect session tokens and other sensitive information from being accessed by JavaScript, and using Subresource Integrity (SRI) attributes to verify the integrity of external scripts and stylesheets.

XSS attacks are one of the most common and dangerous web application vulnerabilities. They can compromise the security and privacy of users and web applications. Therefore, developers should follow the best practices and guidelines to prevent XSS attacks, such as those provided by OWASP[^2^] [^3^] [^4^]. aa16f39245