CVE-2020-9444
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 · uneditedZulip Server before 2.1.3 allows reverse tabnabbing via the Markdown functionality.
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 · moderate confidenceZulip Server before 2.1.3 is vulnerable to reverse tabnabbing through its Markdown rendering. When the Markdown processor generates links with target="_blank" to open in new tabs, it fails to include rel="noopener noreferrer", allowing the opened page to access window.opener and redirect the original page to an attacker-controlled site.
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<= 2.1.3CVSS 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
- None
- User interaction
- Required
- Scope
- Changed
- Confidentiality
- Low
- Integrity
- Low
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/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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Identify your Zulip Server versionCheck your Zulip installation's version by accessing the /api/v1/server_settings endpoint, running 'zulipctl --version' if available, or inspecting the deployment directory for a version marker file. Compare this against the affected range: any version 2.1.3 or earlier.Affected if Your installed version is 2.1.3 or lower.
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Confirm Markdown rendering is in useZulip Server uses Markdown processing for messages by default. Verify that your server processes messages through its Markdown processor by composing a test message with a link in the web or mobile client.Affected if Markdown message processing is enabled (this is the default and typical configuration).
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Inspect rendered HTML for external linksSend a message containing an external URL (such as https://example.com) through your Zulip server. View the message source or inspect the rendered HTML in the browser developer tools. Look for anchor tags with target="_blank" attribute.Affected if External links in rendered messages contain target="_blank" without the rel="noopener noreferrer" attribute.
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Test window.opener access behaviorUsing a test account, post a message with an external link that opens in a new tab. Click the link and, from the opened page, attempt to access window.opener or window.location to confirm whether the original Zulip page can be manipulated.Affected if The opened external page can access window.opener and redirect or modify the original Zulip page.
You are affected if your Zulip Server version is 2.1.3 or earlier AND your installation processes Markdown messages with external links that open in new tabs without rel="noopener noreferrer" attributes.
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.
From vendor dataUpgrade Zulip Server to version 2.1.3 or later, which adds proper rel="noopener noreferrer" attributes to external links rendered from Markdown.
- Consultation1.0 h
- Implementation2.0 h
- Testing1.0 h
- Review / QA1.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,424.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2020-9444 — 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-2020-9444 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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A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.
- 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