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DiscourseApplication

CVE-2021-32764

MEDIUM · 5.4 CVSS v3.1 Published 2021-07-15
Fix available
A fix is available. Upgrade to after 2.7.5 or later.
See remediation →
60/100
Remediation priority · Elevated
Remotely reachable Zero-click

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
Discourse is an open-source discussion platform. In Discourse versions 2.7.5 and prior, parsing and rendering of YouTube Oneboxes can be susceptible to XSS attacks. This vulnerability only affects sites which have modified or disabled Discourse's default Content Security Policy. The issue is patched in `stable` version 2.7.6, `beta` version 2.8.0.beta3, and `tests-passed` version 2.8.0.beta3. As a workaround, ensure that the Content Security Policy is enabled, and has not been modified in a way which would make it more vulnerable to XSS attacks.

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

Discourse versions 2.7.5 and prior contain a stored XSS vulnerability in the YouTube Onebox parsing and rendering functionality. The vulnerability allows injection of malicious scripts when rendering YouTube video embeds, but only affects instances where the Content Security Policy has been modified or disabled.

MitigationUpgrade to Discourse stable version 2.7.6 or later (2.8.0.beta3+) and ensure the default Content Security Policy remains enabled and unmodified to prevent XSS exploitation.

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
DiscourseApplication
Affected:<= 2.7.5= 2.8.0

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
Low
User interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
Low
Availability
None

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/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 Discourse version
    Access the Discourse admin panel and navigate to the About page or check the version indicator in the footer of the admin interface. Alternatively, check the version file in the Discourse installation directory if you have CLI access.
    Affected if The installed version is 2.7.5 or prior, or exactly version 2.8.0 (the initial release). Versions 2.7.6 and later (including 2.8.0.beta3 and later) are not affected.
  2. Confirm YouTube Onebox processing is active
    Verify that your Discourse instance processes YouTube links through the Onebox feature. This can be confirmed by posting a YouTube URL in a post or private message and observing whether it renders as an embedded video player.
    Affected if YouTube Onebox embeds are being rendered on your site. The vulnerability exists in the parsing and rendering logic for YouTube videos; if your site does not process YouTube links as Oneboxes, this specific flaw does not apply.
  3. Examine Content Security Policy configuration
    In the Discourse admin panel, go to the Security settings section and locate the Content Security Policy settings. Verify whether the default CSP has been left enabled or if it has been modified or disabled.
    Affected if The Content Security Policy has been modified to be less restrictive or disabled entirely. The vulnerability is only exploitable when CSP is modified or turned off; the default CSP prevents the XSS from executing.

You are affected if your Discourse version is 2.7.5 or earlier (or exactly 2.8.0), your site processes YouTube video embeds via Onebox, and your Content Security Policy has been modified or disabled.

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 a release after 2.7.5
Interim mitigation

Upgrade to Discourse stable version 2.7.6 or later (2.8.0.beta3+) and ensure the default Content Security Policy remains enabled and unmodified to prevent XSS exploitation.

Fix this in Discourse Scoped from the published advisory
  • Consultation1.0 h
  • Implementation2.0 h
  • Testing1.0 h
  • Review / QA1.0 h
5.0 hours of engineering $890
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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-2021-32764 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