Junglewise Threat Intelligence

CVE-2026-13601: GNOME Yelp sandbox escape and host file disclosure via yelp-xsl

CVE-2026-13601 · Severity: high · CVSS 7.1 · Published 2026-06-29

Technologies: Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 7, Red Hat Enterprise Linux 9, Red Hat Enterprise Linux 10. Vendors: Red Hat, Gnome.

Executive brief

A security vulnerability in the GNOME Yelp help viewer allows malicious sandboxed applications (such as those installed via Flatpak) to bypass security restrictions and steal sensitive files from the host computer. By tricking the system into opening a specially crafted help file, an attacker can silently read private user data and send it to a remote server without any user interaction. This effectively breaks the security 'sandbox' intended to keep isolated applications from accessing the rest of the system.

Technical details

A flaw exists in Yelp and its companion stylesheet component, yelp-xsl, due to an overly permissive Content Security Policy (CSP) implementation. A malicious Flatpak application can exploit the 'org.freedesktop.portal.OpenURI' portal to programmatically launch the host-level Yelp application using the 'ghelp://' or 'mallard' URI schemes. Because Yelp evaluates local XML inclusions (XInclude) and its CSP allows external CSS resource requests, an attacker can embed a CSS 'url()' function within a structured SVG document to exfiltrate the contents of local host files to a remote server. This vulnerability bypasses the Flatpak sandbox isolation and requires no user interaction. The issue is addressed in Yelp version 49.1.

Affected products

  • GNOME Yelp 49.1
  • GNOME yelp-xsl
  • Red Hat Red Hat Enterprise Linux 7
  • Red Hat Red Hat Enterprise Linux 8
  • Red Hat Red Hat Enterprise Linux 9
  • Red Hat Red Hat Enterprise Linux 10

Timeline

  • 2026-05-11: disclosed: Vulnerability details published by Michael Catanzaro
  • 2026-06-29: advisory: NVD and Red Hat published advisory data

References

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