CVE-2021-46872: 
Nim vulnerability analysis and mitigation

An issue was discovered in Nim before version 1.6.2 (CVE-2021-46872). The RST module of the Nim language stdlib, as used in NimForum and other products, permits the javascript: URI scheme which can lead to Cross-Site Scripting (XSS) vulnerabilities in some applications. The vulnerability was fixed in Nim versions 1.6.2 and later, with potential backports to earlier versions. NimForum 2.2.0 also includes the fix (NVD).

The vulnerability exists in the RST (reStructuredText) module of Nim's standard library, which failed to properly sanitize URI schemes in links and image targets. The issue allows the javascript: URI scheme to be processed, potentially enabling XSS attacks. The CVSS v3.1 Base Score is 6.1 (MEDIUM) with the vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N. The vulnerability is classified as CWE-79: Improper Neutralization of Input During Web Page Generation (Cross-site Scripting) (NVD).

If exploited, this vulnerability could allow attackers to execute arbitrary JavaScript code in the context of the victim's browser through XSS attacks. This could potentially lead to theft of sensitive information, session hijacking, or other client-side attacks (NVD).

The primary mitigation is to upgrade to Nim version 1.6.2 or later, which includes the fix for this vulnerability. For NimForum users, upgrading to version 2.2.0 or later is recommended. The fix involves implementing proper URI scheme validation that only allows safe protocols such as http, https, and ftp (Nim Commit).