Vulnerability · Published May 8, 2026 · Assigned by GitHub_M

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

Medium 6.3

In plain English

A medium-severity cross-site scripting in grimmory from grimmory-tools. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.1% (higher than 3% of all known vulnerabilities).

Severity (CVSS 3.1)6.3Medium

Exploit odds (30 days)0.1%top 96.9% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official description

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.

Affected products (as reported)

Vendor	Product	Versions
grimmory-tools	grimmory	< 2.3.1

Weakness: CWE-79, CWE-80 · Vector: CVSS:3.1/AV:L/AC:H/PR:L/UI:R/S:U/C:H/I:H/A:L

References

https://github.com/grimmory-tools/grimmory/security/advisories/GHSA-frv6-5wq5-9p24 x_refsource_CONFIRM
http://github.com/grimmory-tools/grimmory/releases/tag/v2.3.1 x_refsource_MISC