CVE-2026-42451 MEDIUM

CVE-2026-42451: Grimmory: Stored XSS via Malicious EPUB Enables Session Token Theft

Vendor Grimmory-Tools
Product grimmory
Weakness CWE-79 · XSS
Published May 8, 2026
Last update May 12, 2026

CVSS base score

6.3/10
Attack vector Local
Attack complexity High
Privileges required Low
User interaction Required
Confidentiality High
Integrity High

CVSS vector

CVSS:3.1/AV:L/AC:H/PR:L/UI:R/S:U/C:H/I:H/A:L

What the vulnerability does

01Description

Grimmory is a self-hosted digital library. Prior to version 2.3.1, a stored cross-site scripting (XSS) vulnerability in Grimmory's browser-based EPUB reader allows an attacker to embed arbitrary JavaScript in a crafted EPUB file. When a victim opens the book, the script executes in their browser with full access to the Grimmory application's session context. This can enable session token theft and account takeover, including administrative access if an administrator opens the affected book. This issue has been patched in version 2.3.1.

Key dates

02Disclosure timeline

May 8, 2026 CVE published
May 12, 2026 Record updated