CVE-2018-11627: Sinatra Cross-site Scripting vulnerability
Summary
CVE-2018-11627: Sinatra Cross-site Scripting vulnerability. Affects sinatra versions >= 2.0.0, < 2.0.2. Fixed in 2.0.2. How to fix ↓
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Background
Sinatra is a Ruby web application framework that allows developers to quickly build web applications. It is known for its simplicity and flexibility. The vulnerability in question affects versions of Sinatra before 2.0.2. Sinatra is vulnerable to a cross-site scripting (XSS) attack that occurs when a params parser exception triggers a 400 Bad Request page. This vulnerability can potentially allow an attacker to inject malicious code into the application and execute it within the context of the user's browser.
Vulnerability Detail
The vulnerability arises due to inadequate input validation and sanitization of user-supplied data. When an exception occurs during the parsing of request parameters, Sinatra generates a 400 Bad Request page that includes the user-supplied data without proper escaping or encoding. This allows an attacker to craft a malicious request that includes JavaScript code, which will be executed when the page is rendered in the victim's browser. The impact of this vulnerability can range from stealing sensitive user information to performing actions on behalf of the user.
How To Fix
Latest published version: 4.2.1 as of 23 Oct 2026
gem install sinatra -v 4.2.1Upgrading to it may include breaking changes; the version below is the minimum fixed release for this vulnerability.
If you need the minimum change
2.0.2
This is the first release that contains the fix.
gem install sinatra -v 2.0.2Tip — Not sure which version your app runs? Vulert can match this fix to it. Scan free →
Workaround
A possible workaround for this vulnerability is to manually escape or encode user-supplied data before displaying it in the 400 Bad Request page. This can be done using appropriate encoding functions provided by the programming language or framework being used. However, this workaround is not recommended as it may introduce additional complexities and potential vulnerabilities if not implemented correctly. It is strongly advised to upgrade to the patched version of Sinatra instead.
Conclusion
The Sinatra Cross-site Scripting vulnerability (CVE-2018-11627) is a moderate-severity vulnerability that affects versions of Sinatra before 2.0.2. It allows attackers to inject malicious scripts into the application, potentially leading to the theft of sensitive information or unauthorized actions. To mitigate this vulnerability, it is recommended to upgrade to the patched version of Sinatra (2.0.2 or later) or implement proper input validation and sanitization measures. For further support on vulnerability remediation, please contact DevNack.com.
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FAQ
Cross-site scripting (XSS) is a type of security vulnerability that allows attackers to inject malicious scripts into web pages viewed by other users. This can lead to various attacks, such as stealing sensitive information or performing actions on behalf of the user.
The vulnerability in Sinatra occurs when a params parser exception triggers a 400 Bad Request page. This page includes user-supplied data without proper escaping or encoding, allowing an attacker to inject malicious scripts.
The impact of this vulnerability can vary depending on the attacker's intentions. It can range from stealing sensitive user information, such as login credentials or personal data, to performing actions on behalf of the user, such as making unauthorized changes or transactions.
To fix this vulnerability, it is recommended to upgrade to Sinatra version 2.0.2 or later. This version includes a fix for the XSS vulnerability. Alternatively, you can manually escape or encode user-supplied data before displaying it in the 400 Bad Request page, but this is not recommended as it may introduce additional complexities and potential vulnerabilities.
Yes, you can use Vulert's playground (https://vulert.com/scanner) to check if your application is affected by this vulnerability. Vulert monitors and alerts in real-time for open-source vulnerabilities, and you can upload your manifest file (e.g., package-lock.json) to check for vulnerabilities without requiring access to the code or installation.
References
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