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DiscourseApplication

CVE-2025-48877

CRITICAL · 9.8 CVSS v3.1 Published 2025-06-09
Fix available
A fix is available. Upgrade to 3.4.4 / 3.5.0 or later.
See remediation →
100/100
Remediation priority · Urgent
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 version 3.4.4 of the `stable` branch, version 3.5.0.beta5 of the `beta` branch, and version 3.5.0.beta6-dev of the `tests-passed` branch, Codepen is present in the default `allowed_iframes` site setting, and it can potentially auto-run arbitrary JS in the iframe scope, which is unintended. This issue is patched in version 3.4.4 of the `stable` branch, version 3.5.0.beta5 of the `beta` branch, and version 3.5.0.beta6-dev of the `tests-passed` branch. As a workaround, the Codepen prefix can be removed from a site's `allowed_iframes`.

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 includes Codepen in its default allowed_iframes site setting, which can allow arbitrary JavaScript execution through malicious Codepen embeds. An attacker could embed specially crafted Codepen content that auto-executes JavaScript in the context of the Discourse site, leading to session hijacking and unauthorized actions.

MitigationEither upgrade to version 3.4.4 (stable), 3.5.0.beta5 (beta), or 3.5.0.beta6-dev (tests-passed), or manually remove the Codepen prefix from the allowed_iframes site setting as a workaround.

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:< 3.4.4< 3.5.0= 3.5.0

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
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

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, navigate to /admin, or check the VERSION file in the Discourse installation directory. Alternatively, run `git log -1 --format='%H %s'` from the Discourse root directory.
    Affected if The installed version is less than 3.4.4, less than 3.5.0, or exactly 3.5.0
  2. Verify allowed_iframes site setting
    In the Discourse admin panel, go to Settings > Security or navigate to /admin/site_settings/category/all?filter=iframe. Look for the allowed_iframes setting and examine its value.
    Affected if The allowed_iframes setting contains 'codepen' (case-insensitive) in the list of allowed iframe sources
  3. Confirm iframe embedding is enabled
    In admin panel, verify that the embedding feature is enabled by checking settings under Settings > Security or Settings > Posting. Ensure that allow_embedding is not disabled.
    Affected if Embedding is enabled (the allowed_iframes setting is accessible and not empty)

A defender is affected if their Discourse version is less than 3.4.4, less than 3.5.0, or exactly 3.5.0 AND the allowed_iframes site setting contains the Codepen prefix.

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 3.4.4 / 3.5.0 or later
Fixed in 3.4.43.5.0
Interim mitigation

Either upgrade to version 3.4.4 (stable), 3.5.0.beta5 (beta), or 3.5.0.beta6-dev (tests-passed), or manually remove the Codepen prefix from the allowed_iframes site setting as a workaround.

Recommended fix High confidence

Discourse 3.4.4 (stable branch)

  1. Upgrade Discourse to version 3.4.4 (stable branch) or later
  2. Alternatively, if immediate upgrade is not possible, navigate to the Discourse admin panel
  3. Go to the Site Settings section
  4. Find the 'allowed_iframes' setting
  5. Remove the Codepen prefix (codepen.io) from the allowed iframe sources list
  6. Save the settings

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

Fix this in Discourse Scoped from the published advisory
  • Consultation1.0 h
  • Implementation1.0 h
  • Testing2.0 h
  • Review / QA1.0 h
5.0 hours of engineering $860
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,376.

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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-2025-48877 in production — separate from our analysis above.

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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