What is CVE-2026-42451?

CVE-2026-42451 is a medium-severity vulnerability in Grimmory-Tools Grimmory, classified under Cross-site Scripting. CVSS score: 6.3/10. Published 2026-05-08.

How severe is CVE-2026-42451?

Medium severity. CVSS v3 base score is 6.3 out of 10.

XSS in Grimmory-Tools Grimmory

CVE-2026-42451

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.

Vulnerability class: XSS (Cross-Site Scripting)

EPSS: 0.001 (3.4th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 6.3 (Medium). Vector: CVSS:3.1/AV:L/AC:H/PR:L/UI:R/S:U/C:H/I:H/A:L.

Affected products

Grimmory-tools Grimmory — versions < 2.3.1

Weakness classification (CWE)

References

security-advisories@github.com (x_refsource_MISC)
security-advisories@github.com (x_refsource_CONFIRM)

Frequently asked questions

What is CVE-2026-42451?: CVE-2026-42451 is a medium-severity vulnerability in Grimmory-Tools Grimmory, classified under Cross-site Scripting. CVSS score: 6.3/10. Published 2026-05-08.
How severe is CVE-2026-42451?: Medium severity. CVSS v3 base score is 6.3 out of 10.