Is CVE-2026-42451 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-42451 being exploited in the wild.

How severe is CVE-2026-42451?

Medium severity, with a CVSS score of 6.3, published 8 May 2026.

Which products and versions are affected?

Grimmory-Tools Grimmory < 2.3.1, <= 2.3.0.

Is there a fix for CVE-2026-42451?

A patch was published on 2026-04-22: Fix merged and version 2.3.1 released Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-42451 attacked?

It is attacked with local access, in a network appliance.

Am I affected by CVE-2026-42451?

Check whether you run Grimmory-Tools Grimmory at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-42451: Grimmory stored XSS in EPUB reader via insecure iframe sandbox

Q: Is there a fix for CVE-2026-42451?

A patch was published on 2026-04-22: Fix merged and version 2.3.1 released Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

Q: How is CVE-2026-42451 attacked?

It is attacked with local access, in a network appliance.

Q: Am I affected by CVE-2026-42451?

Check whether you run Grimmory-Tools Grimmory at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-42451 · Severity: medium · CVSS 6.3 · Published 2026-05-08

Grimmory is a self-hosted digital library for managing and reading electronic books. A security flaw in its built-in book reader allows a malicious actor to hide harmful code inside an EPUB file. If a user or administrator opens the infected book, the attacker can steal their login session, potentially leading to full account takeover and unauthorized access to the entire library.

Technologies: Grimmory-Tools Grimmory. Vendors: Grimmory-Tools.

Quick answers

Is CVE-2026-42451 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-42451 being exploited in the wild.
How severe is CVE-2026-42451?: Medium severity, with a CVSS score of 6.3, published 8 May 2026.
Which products and versions are affected?: Grimmory-Tools Grimmory < 2.3.1, <= 2.3.0.
Is there a fix for CVE-2026-42451?: A patch was published on 2026-04-22: Fix merged and version 2.3.1 released Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-42451 attacked?: It is attacked with local access, in a network appliance.
Am I affected by CVE-2026-42451?: Check whether you run Grimmory-Tools Grimmory at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

A stored cross-site scripting (XSS) vulnerability exists in Grimmory's browser-based EPUB reader due to an insecure iframe sandbox configuration. The application embeds the foliate-js reader using an iframe that simultaneously enables both 'allow-scripts' and 'allow-same-origin' attributes. This combination allows JavaScript within the EPUB (which is essentially a ZIP of HTML/JS) to bypass origin-based isolation and access the parent window's DOM and localStorage. An attacker with upload privileges can provide a malicious EPUB that, when viewed, exfiltrates session tokens or performs authenticated API requests on behalf of the victim. The vulnerability is addressed in version 2.3.1 by removing 'allow-scripts' from the iframe sandbox and implementing a Content Security Policy (CSP).

Affected products

grimmory-tools grimmory < 2.3.1

Timeline

2026-03-19: disclosed: Vulnerability reported to Grimmory via GitHub private security disclosure
2026-04-22: patched: Fix merged and version 2.3.1 released
2026-05-08: advisory: CVE-2026-42451 published

References

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