CVE-2026-39426
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 · uneditedMaxKB is an open-source AI assistant for enterprise. Versions 2.7.1 and below contain a Stored Cross-Site Scripting (XSS) vulnerability where the frontend's MdRenderer.vue component parses custom <iframe_render> tags from LLM responses or Application Prologue configurations, bypassing standard Markdown sanitization and XSS filtering. The unsanitized HTML content is passed to the IframeRender.vue component, which renders it directly into an <iframe> via the srcdoc attribute configured with sandbox="allow-scripts allow-same-origin". This can be a dangerous combination, allowing injected scripts to escape the iframe and execute JavaScript in the parent window using window.parent. Since the Prologue is rendered for any user visiting an application's chat interface, this results in a high-impact Stored XSS that can lead to session hijacking, unauthorized actions, and sensitive data exposure. This issue has been fixed in version 2.8.0.
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 confidenceMaxKB versions 2.7.1 and below have a stored XSS in the MdRenderer.vue component, which parses unsanitized custom <iframe_render> tags from LLM responses or Application Prologue configurations. These tags are passed to IframeRender.vue and rendered in an iframe using srcdoc with sandbox="allow-scripts allow-same-origin", allowing injected scripts to escape the iframe and execute in the parent window via window.parent.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data< 2.8.0CVSS 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
- Network
- Complexity
- Low
- Privileges
- Low
- User interaction
- Required
- Scope
- Changed
- Confidentiality
- Low
- Integrity
- Low
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
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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Determine MaxKB installation versionCheck your installed MaxKB version using the package manager, docker image tag, or application UI (typically found in Settings > About or the login page footer). Compare it against the affected range: versions prior to 2.8.0 are vulnerable.Affected if The installed version is 2.7.1 or below, or any version less than 2.8.0.
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Identify Application Prologue configurationsAccess MaxKB administrative interface and navigate to Application settings. Look for any configured Prologue (initial prompt or welcome message) that may contain custom HTML or markdown with iframe_render tags.Affected if An Application Prologue configuration exists and contains custom iframe_render tags that could be interpreted by MdRenderer.vue.
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Review LLM response processingCheck if MaxKB is configured to process and render markdown responses from LLM integrations. Inspect application logs or network traffic for instances where the system renders LLM-generated content containing custom tags.Affected if MaxKB processes LLM responses that may contain the custom iframe_render tag syntax.
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Inspect rendered output for sandbox attributesIf you have access to the frontend code or browser developer tools, examine how iframe_render tags are rendered. Look for iframe elements with srcdoc attributes and sandbox permissions including allow-same-origin.Affected if The application renders iframe elements with sandbox="allow-scripts allow-same-origin" on iframe_render tags, which enables the window.parent bypass.
You are affected if MaxKB version is below 2.8.0 AND the system either uses Application Prologue configurations or processes LLM responses that could contain custom iframe_render tags.
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 · scoped2.8.0
Upgrade to MaxKB version 2.8.0 or later, which contains the fix for this vulnerability.
2.8.0
- 1. Back up your current MaxKB installation and database before upgrading.
- 2. Upgrade MaxKB to version 2.8.0 using your deployment method (e.g., Docker pull, pip install, or package manager).
- 3. After upgrading, clear any cached browser data and session cookies.
- 4. Verify the upgrade by checking the MaxKB version indicator in the application.
- 5. Test that Application Prologue configurations and LLM responses with custom tags are now properly sanitized and do not execute arbitrary JavaScript.
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation3.0 h
- Implementation6.0 h
- Testing6.0 h
- Review / QA3.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-39426 — 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-2026-39426 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