CVE-2021-39161
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 · uneditedDiscourse is an open source platform for community discussion. In affected versions category names can be used for Cross-site scripting(XSS) attacks. This is mitigated by Discourse's default Content Security Policy and this vulnerability only affects sites which have modified or disabled or changed Discourse's default Content Security Policy have allowed for moderators to modify categories. This issue is patched in the latest stable, beta and tests-passed versions of Discourse. Users are advised to 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 confidenceIn affected versions of Discourse, category names can contain malicious JavaScript that executes via Cross-site scripting (XSS). This attack vector is normally blocked by Discourse's default Content Security Policy (CSP), but sites that have modified, disabled, or weakened their CSP and allow moderators to create or modify categories remain vulnerable.
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< 2.7.8= 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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Check Discourse versionNavigate to /admin dashboard or check the version file in your Discourse installation directory. Common locations: /var/discourse/containers/app.yml or via the admin UI at /aboutAffected if Installed version is less than 2.7.8 or exactly 2.8.0
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Inspect Content Security Policy configurationExamine your Discourse CSP settings in the admin panel under /admin/site_settings/category/all_results?filter=content_security_policy or check nginx/apache config for CSP headersAffected if CSP is disabled, missing, or contains 'unsafe-inline' in script-src directives that weaken XSS protection
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Verify moderator permissions for categoriesCheck user permissions in /admin/users/list/Moderators and review category permission settings in /categories - specifically whether moderators have 'Edit' or 'Full' access to categoriesAffected if Moderators have ability to create new categories or edit existing category names
A user is affected if their Discourse version is below 2.7.8 or exactly 2.8.0 AND the Content Security Policy has been weakened (allowing unsafe-inline scripts) AND moderators can create or modify category names.
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 · scoped2.7.8
Ensure Content Security Policy is enabled and not modified in a way that weakens XSS protection; update to the latest stable, beta, or tests-passed version of Discourse.
2.7.9 or latest stable release
- Upgrade Discourse to version 2.7.9 or later, or to the latest stable release
- After upgrading, verify the Content Security Policy (CSP) remains enabled and has not been modified to reduce XSS protection
- Confirm that only trusted moderators have permission to modify categories
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation2.0 h
- Implementation3.0 h
- Testing2.0 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 $2,272.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-39161 — 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-2021-39161 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