CVE-2020-15692: 
Nim vulnerability analysis and mitigation

CVE-2020-15692 affects Nim version 1.2.4 and earlier versions, specifically in the standard library browsers component. The vulnerability was discovered on July 9, 2020, and was fixed with the release of version 1.2.6 on July 30, 2020. The issue exists in the browsers.openDefaultBrowser functionality, which mishandles URL arguments by failing to validate that the provided input is actually a URL (Consensys Diligence, NVD).

The vulnerability occurs in the browsers.openDefaultBrowser() function, which internally calls shellExecuteW on Windows and execShellCmd with the OS's open command (xdg-open on Linux, open on MacOS). The implementation fails to validate whether the input is a legitimate URL, allowing attackers to pass arbitrary arguments to the underlying open command. On Windows, the attacker can control the lpFile argument to shellExecuteW, while on MacOS, they can control the first argument to the open command (OSS Security).

An attacker who can control the URL input to browsers.openDefaultBrowser() can execute arbitrary registered system commands through command injection. On Windows, this could lead to opening arbitrary local files, while on MacOS, the attacker could launch applications or execute commands within the constraints of the open command's functionality (Consensys Diligence).

The vulnerability is easily exploitable through simple proof-of-concept code. For example, on MacOS, an attacker can launch the calculator application by passing '-bcom.apple.calculator' as the URL argument. The vulnerability can also be exploited to open arbitrary files or execute system commands within the context of the application (OSS Security).

The vulnerability was fixed in Nim version 1.2.6. The fix involves validating that the URL is actually a URL and filtering non-printable characters or URL-encoding them. Users are advised to upgrade to version 1.2.6 or later to address this security issue (Nim Blog).