CVE-2020-15230: 
Swift vulnerability analysis and mitigation

Vapor is a web framework for Swift that contained a critical vulnerability (CVE-2020-15230) in versions 4.0.0-rc.2.5 through 4.29.3. The vulnerability was discovered in the FileMiddleware component and was patched in version 4.29.4. This security flaw allowed attackers to access data at arbitrary filesystem paths on the same host as the application (GitHub Advisory).

The vulnerability existed in the FileMiddleware component where percent-encoded relative paths were not properly handled. The issue stemmed from how the middleware processed URL paths before accessing files on the filesystem. The fix involved improving the handling of percent-decoded paths and adding additional security checks to prevent unauthorized file access (GitHub Commit).

The vulnerability allowed attackers to access arbitrary files on the same host where the Vapor application was running. This could potentially lead to unauthorized access to sensitive system files and data exposure (GitHub Advisory).

The vulnerability could be exploited by sending specially crafted HTTP requests with percent-encoded relative paths to an application using FileMiddleware. No special privileges were required to exploit this vulnerability (GitHub Advisory).

Users are advised to upgrade to Vapor version 4.29.4 or later which contains the security fix. Alternatively, if immediate upgrading is not possible, users can disable FileMiddleware as a temporary workaround (GitHub Advisory).