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Zulip ServerApplication · Zulip

CVE-2020-9445

MEDIUM · 6.1 CVSS v3.1 Published 2020-04-20
Fix available
A fix is available. Upgrade to 2.1.3 or later.
See remediation →
68/100
Remediation priority · Elevated
Remotely reachable No privileges

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 · unedited
Zulip Server before 2.1.3 allows XSS via the modal_link feature in 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 · high confidence

Cross-site scripting (XSS) vulnerability in Zulip Server's Markdown processing through the modal_link feature, affecting versions prior to 2.1.3. Attackers can inject malicious scripts via crafted Markdown content using the modal_link feature.

MitigationUpgrade Zulip Server to version 2.1.3 or later to remediate the XSS vulnerability in the modal_link Markdown feature.

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
Zulip ServerApplication
Affected:< 2.1.3

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
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 checks

Work through these to decide whether this CVE applies to you.

  1. Identify installed Zulip Server version
    Run the command: cat /etc/zulip/version.conf or check the Zulip admin interface under 'Server status' for the exact version number
    Affected if The version listed is less than 2.1.3
  2. Confirm Markdown processing is active
    Verify that Zulip is configured to accept Markdown-formatted messages in streams or private messages. Check admin settings at /#settings/organization for 'Markdown' or 'message content' settings
    Affected if Markdown message processing is enabled (this is the default setting)
  3. Check for modal_link feature usage
    Search server logs and message content for occurrences of the modal_link markdown syntax (typically [text](modal://content)) being processed. Review /var/log/zulip/server.log for markdown rendering activity
    Affected if Users have posted or can post content using the modal_link markdown feature (format: [link text](modal://...))

A user is affected if their Zulip Server version is below 2.1.3 AND the Markdown feature (default) is enabled, allowing message content with the modal_link syntax to be processed and rendered.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

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 data
Upgrade available Upgrade to 2.1.3 or later
Fixed in 2.1.3
Interim mitigation

Upgrade Zulip Server to version 2.1.3 or later to remediate the XSS vulnerability in the modal_link Markdown feature.

Fix this in Zulip Server Scoped from the published advisory
  • Consultation3.0 h
  • Implementation6.0 h
  • Testing5.0 h
  • Review / QA3.0 h
17.0 hours of engineering $2,970
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $4,752.

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2020-9445 in production — separate from our analysis above.

No notes yet

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What this is

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.

What belongs here
  • 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