Grimmory: Stored XSS via Malicious EPUB Enables Session Token Theft

published 2026-05-08 6 mo ago modified 2026-07-24 3 mo ago also EUVD-2026-28861

cvss: 6.3; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.1%; EPSS 0.1% chance of exploitation in 30 days, percentile 3%
public exploits: 0; none known

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.

Patch / fix

links 1

github.com/grimmory-tools/grimmory/releases/tag/v2.3.1 release

CISA SSVC

Exploitation: none
Automatable: no
Technical impact: total
Assessed: 5 mo ago (2026-05-12)

Exploit prediction

0.14% chance of exploitation in the next 30 days, higher than 3% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
CNA	3.1	6.3	CVSS:3.1/AV:L/AC:H/PR:L/UI:R/S:U/C:H/I:H/A:L

Affected products

grimmory-tools grimmory

Classification

Weakness

CWE-79 Improper Neutralization of Input During Web Page Generation
CWE-80 Improper Neutralization of Script-Related HTML Tags in a Web Page

References

Sources

CVE List CVE-2026-42451
NVD CVE-2026-42451

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary