# CVE-2026-93955: grimmory authorization bypass in Kobo download endpoint

Source: https://junglewise.ai/threats/cve-2026-93955-a-vulnerability-was-detected-in-grimmory-tools-grimmory-up-to-3-3  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-19. Updated: 2026-09-26  
License: CC BY 4.0 with a link back

CVE-2026-93955 · Severity: medium · CVSS 4.3 · Published 2026-09-19

Grimmory is a self-hosted library application for managing ebooks, comics, and audiobooks. A flaw in the Kobo book download endpoint allows users with a valid Kobo token to download book files from libraries they should not have access to, potentially exposing content across the entire library without proper authorization checks.

Technologies: [Grimmory-Tools Grimmory](https://junglewise.ai/threats/technologies/grimmory). Vendors: [Grimmory-Tools](https://junglewise.ai/threats/vendors/grimmory-tools).

## Quick answers

**Is CVE-2026-93955 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-93955 being exploited in the wild.

**How severe is CVE-2026-93955?** Medium severity, with a CVSS score of 4.3, published 19 September 2026.

**Which products and versions are affected?** Grimmory-Tools Grimmory up to 3.3.3 and 3.4.1.

**Is there a fix for CVE-2026-93955?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-93955 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-93955?** 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

An authorization bypass exists in the streamFileToResponse function of the Kobo download endpoint (GET /api/kobo/{token}/v1/books/{bookId}/download) due to missing library-level access control validation. A user with the syncKobo permission and knowledge of arbitrary book IDs can download EPUB or CBX files from libraries to which they are not assigned. The same validateBookContentAccess check used in OPDS and Komga paths is absent in the Kobo path, allowing the vulnerability to bypass intended multi-library access restrictions.

## Affected products

- grimmory-tools grimmory up to 3.3.3 and 3.4.1

## Timeline

- 2026-09-19: disclosed
- other: Issue #2431 closed but no patching commit identified

## References

- [https://github.com/grimmory-tools/grimmory/](https://github.com/grimmory-tools/grimmory/)
- [https://github.com/grimmory-tools/grimmory/issues/2431](https://github.com/grimmory-tools/grimmory/issues/2431)

## Related threats

- [grimmory Settings API authorization bypass](https://junglewise.ai/threats/cve-2026-93954-a-security-vulnerability-has-been-detected-in-grimmory-tools)
- [Grimmory stored XSS in EPUB reader via insecure iframe sandbox](https://junglewise.ai/threats/cve-2026-42451-grimmory-stored-xss-in-epub-reader-via-insecure-iframe-sandbox)