Medium [CVE-2026-13323] Supply chain attack via cross-site scripting

In Open VSX Registry before 1.0.2, the /vscode/unpkg/ endpoint serves user-supplied HTML files with Content-Type: text/html and without a Content-Security-Policy or Content-Disposition: attachment response header.

An unauthenticated attacker can register a publisher account, upload a VSIX containing a crafted HTML payload, and induce an authenticated user to visit the resulting URL.

The browser renders the file inline in the open-vsx.org origin context, enabling session token exfiltration, persistent Personal Access Token (PAT) generation, and unauthorized publication of malicious extension versions.

Because Open VSX extensions are distributed to VS Code, VSCodium, Cursor, Windsurf, and compatible editors, a compromised extension update constitutes a supply chain attack against all downstream users. This Moderate flaw in Open VSX Registry, as utilized by Red Hat OpenShift Dev Spaces, involves a cross-site scripting vulnerability.

An attacker with a registered publisher account could upload a crafted extension, and if an authenticated user is enticed to visit a specific URL, their session tokens could be exfiltrated, or unauthorized extension publications could occur. This requires both attacker prerequisites and user interaction, which limits the overall impact.

Red Hat severity: Moderate — CVSS 5.4 (CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N). Weakness: CWE-79.