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DiscourseApplication

CVE-2026-33427

HIGH · 7.5 CVSS v3.1 Published 2026-03-21
Fix available
A fix is available. Upgrade to 2026.1.2 / 2026.2.1 or later.
See remediation →
84/100
Remediation priority · High
Remotely reachable No privileges 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. Prior to versions 2026.3.0-latest.1, 2026.2.1, and 2026.1.2, an unauthenticated attacker can cause a legitimate Discourse authorization page to display an attacker-controlled domain, facilitating social engineering attacks against users. Versions 2026.3.0-latest.1, 2026.2.1, and 2026.1.2 contain a patch. No known workarounds are available.

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

This is an open redirect/URL manipulation vulnerability in Discourse's OAuth/authorization flow. An unauthenticated attacker can influence the authorization page to display an attacker-controlled domain, facilitating credential theft or session hijacking via social engineering.

MitigationUpgrade Discourse to version 2026.3.0-latest.1, 2026.2.1, or 2026.1.2. No workarounds are available.

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:>= 2026.1.0, < 2026.1.2>= 2026.2.0, < 2026.2.1= 2026.3.0

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

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/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. Determine installed Discourse version
    Access the Discourse admin panel at /admin, or run `cd /var/www/discourse && git describe --tags` or check the version file in the Discourse installation directory
    Affected if The version falls within >= 2026.1.0 and < 2026.1.2, OR >= 2026.2.0 and < 2026.2.1, OR equals 2026.3.0
  2. Verify OAuth authorization is configured
    Check if any OAuth provider (Google, GitHub, Facebook, custom SAML, OIDC, etc.) is enabled in the Discourse admin panel under /admin/plugins or by inspecting the site settings database
    Affected if OAuth or any external authentication provider is enabled and configured for user login
  3. Inspect OAuth redirect URL configuration
    Review the allowed_redirect_domains or similar OAuth callback/whitelist settings in Discourse admin or site settings. Look for entries that may permit external untrusted domains
    Affected if The redirect URL whitelist contains domains not controlled by the organization or allows wildcard/arbitrary domain redirects
  4. Check for suspicious authorization callback URLs
    Examine server access logs or OAuth provider configuration for recent authorization requests with unusual redirect parameters pointing to unfamiliar domains
    Affected if Authorization requests are being logged with redirect URLs pointing to domains other than the legitimate Discourse instance

A user is affected if their Discourse version is one of the vulnerable releases AND OAuth/external authentication is enabled, regardless of redirect configuration state since the vulnerability allows attacker-influenced redirect manipulation during the OAuth flow.

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.

dbcve · scoped
Upgrade available Upgrade to 2026.1.2 / 2026.2.1 or later
Fixed in 2026.1.22026.2.1
Interim mitigation

Upgrade Discourse to version 2026.3.0-latest.1, 2026.2.1, or 2026.1.2. No workarounds are available.

Recommended fix High confidence

2026.1.2 (for 2026.1.x branch), 2026.2.1 (for 2026.2.x branch), or 2026.3.0-latest.1 (for 2026.3.x branch)

  1. Identify the currently installed Discourse version by checking the /admin/about page or running `git rev-parse HEAD` in the Discourse directory
  2. Determine which version branch you are on (2026.1.x, 2026.2.x, or 2026.3.x)
  3. If on 2026.1.x branch: upgrade to version 2026.1.2
  4. If on 2026.2.x branch: upgrade to version 2026.2.1
  5. If on 2026.3.x branch: upgrade to version 2026.3.0-latest.1
  6. Run the Discourse upgrade commands (typically `./launcher rebuild app` for Docker installations)
  7. Verify the upgrade was successful by checking the version in /admin/about
  8. Confirm the vulnerability is patched by testing the OAuth/authorization flow to ensure the redirect domain is properly validated
Caveat Standard Discourse minor version upgrades typically have minimal breaking changes, but review the release notes for your specific version branch before upgrading

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Discourse Scoped from the published advisory
  • Consultation3.0 h
  • Implementation4.0 h
  • Testing6.0 h
  • Review / QA3.0 h
16.0 hours of engineering $2,760
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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-2026-33427 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