File Traversal affecting SVG files on Nextcloud Server

Vulnerability Description

Nextcloud is an open-source, self-hosted productivity platform. Prior to versions 20.0.13, 21.0.5, and 22.2.0, a file traversal vulnerability makes an attacker able to download arbitrary SVG images from the host system, including user provided files. This could also be leveraged into a XSS/phishing attack, an attacker could upload a malicious SVG file that mimics the Nextcloud login form and send a specially crafted link to victims. The XSS risk here is mitigated due to the fact that Nextcloud employs a strict Content-Security-Policy disallowing execution of arbitrary JavaScript. It is recommended that the Nextcloud Server be upgraded to 20.0.13, 21.0.5 or 22.2.0. There are no known workarounds aside from upgrading.

References

• https://github.com/nextcloud/security-advisories/security/advisories/GHSA-jp9c-vpr3-m5rf
• https://github.com/nextcloud/server/pull/28726
• https://hackerone.com/reports/1302155
• https://security.gentoo.org/glsa/202208-17