CVE-2020-9443: 
Zulip vulnerability analysis and mitigation

Zulip Desktop before version 4.0.3 contained a critical security vulnerability (CVE-2020-9443) where untrusted content was loaded in an Electron webview with web security disabled. This vulnerability was particularly severe in Zulip Desktop 2.3.82. The issue was discovered and reported by Matt Austin, with the vulnerability being publicly disclosed on February 29, 2020 (Zulip Blog).

The vulnerability stems from the disabled web security settings in the Electron webview component, which compromised Zulip's security model for uploaded files. The security model typically relies on the browser (Electron in this case) to enforce web security protocols. This configuration could be exploited for cross-site scripting (XSS) attacks in multiple ways (Zulip Blog).

This vulnerability was classified as critical because it bypassed Zulip's security model for uploaded files. The disabled web security in the Electron webview could allow attackers to perform cross-site scripting attacks, potentially compromising user data and system security (Zulip Blog).

The vulnerability was patched in Zulip Desktop 4.0.3. Users were advised to manually update their installations, particularly those running version 2.3.82 which couldn't auto-update. A large, red notice was implemented in the Zulip UI to alert users of version 2.3.82 about the broken auto-update feature and direct them to download the latest version from zulipchat.com/apps (Zulip Blog).

In response to this vulnerability, Zulip's development team indicated they would be making major changes to how the Electron desktop app is maintained (Zulip Blog).