CVE-2026-27166

What it is

Discourse is an open source discussion platform. Prior to versions 2026.3.0-latest.1, 2026.2.1 and 2026.1.2, insufficient cleanup in the default Codepen allowed iframes value allows an attacker to trick a user into changing the URL of the main page. This issue has been fixed in versions 2026.3.0-latest.1, 2026.2.1 and 2026.1.2. To workaround this issue, remove Codepen from the list of allowed iframes.

At a glance

Exploitability

Can be exploited over the network with a low-privilege account, but needs a user to act. Limited direct impact.

Exploit odds

0.2% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2026-03-19 21:17 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-06-17 10:26 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 0.2% in the next 30 days (EPSS).
• Severity: 4.1 MEDIUM (CVSS).
• Fix: a patch or advisory is linked.

Details

Published

2026-03-19 21:17 UTC

Last modified

2026-06-17 10:26 UTC

Exploit probability

0.2% · EPSS, next 30 days

Weakness

CWE-80

Record status

Analyzed

Affected

• Discourse < 2026.3.0
• Discourse < 2026.1.2
• Discourse < 2026.2.1
• Discourse 2026.3.0

Attack profile CVSS 3.1 · 4.1

Attack vector

Network

Complexity

Low

Privileges needed

Low

User interaction

Required

Scope

Changed

Confidentiality

None

Integrity

Low

Availability

None

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2026-27166.md and follow it. Check whether this project is affected by CVE-2026-27166. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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