CVE-2026-42451
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedGrimmory 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.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceGrimmory's browser-based EPUB reader fails to sanitize content from uploaded EPUB files, allowing attackers to embed malicious JavaScript. When users open crafted EPUB files, the embedded script executes within their browser session, granting attackers access to session tokens and cookies. This enables complete account takeover, including administrative accounts if an admin opens the malicious book.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Local
- Complexity
- High
- Privileges
- Low
- User interaction
- Required
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- Low
CVSS:3.1/AV:L/AC:H/PR:L/UI:R/S:U/C:H/I:H/A:L
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Identify installed Grimmory versionLocate the Grimmory application and check its version number in the software manifest, about page, or installation directory metadataAffected if The version is lower than 2.3.1 (e.g., 2.3.0, 2.2.x, or earlier)
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Verify EPUB reader feature is activeConfirm that the browser-based EPUB reader module is enabled and accessible within the applicationAffected if The EPUB reader feature is enabled and users can open EPUB files through the application interface
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Confirm user-facing EPUB file handlingDetermine whether the application allows users to upload, import, or open EPUB files through the web interfaceAffected if Users can load custom EPUB files into the reader, providing an attack vector for crafted malicious files
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Check for content security policy enforcementInspect HTTP response headers from the application for Content-Security-Policy directives that restrict script executionAffected if CSP headers are missing or permissive, allowing inline scripts to execute within the session context
You are affected if Grimmory version is below 2.3.1 AND the browser-based EPUB reader feature is enabled and accessible to users who can load custom EPUB files.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scopedUpgrade Grimmory to version 2.3.1 or later. If immediate upgrade is not possible, restrict EPUB file uploads and disable the browser-based reader until patching is feasible.
Grimmory version 2.3.1
- Upgrade Grimmory to version 2.3.1 or later to remediate the stored XSS vulnerability in the EPUB reader
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation3.0 h
- Implementation8.0 h
- Testing4.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $4,800.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-42451 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-42451 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
- No spam, self-promotion, credentials, or personal data