VDB-351806 · CVE-2026-27166 · GHSA-h653-cq78-vjj2

Discourse up to 2026.1.1/2026.2.0 iFrame cross site scripting

CVSS Meta Temp Score CVSS is a standardized scoring system to determine possibilities of attacks. The Temp Score considers temporal factors like disclosure, exploit and countermeasures. The unique Meta Score calculates the average score of different sources to provide a normalized scoring system.	Current Exploit Price (≈) Our analysts are monitoring exploit markets and are in contact with vulnerability brokers. The range indicates the observed or calculated exploit price to be seen on exploit markets. A good indicator to understand the monetary effort required for and the popularity of an attack.	CTI Interest Score Our Cyber Threat Intelligence team is monitoring different web sites, mailing lists, exploit markets and social media networks. The CTI Interest Score identifies the interest of attackers and the security community for this specific vulnerability in real-time. A high score indicates an elevated risk to be targeted for this vulnerability.
4.3	$0-$5k	0.00

Summaryinfo

A vulnerability classified as problematic was found in Discourse up to 2026.1.1/2026.2.0. This issue affects some unknown processing of the component iFrame Handler. Such manipulation leads to cross site scripting. This vulnerability is documented as CVE-2026-27166. The attack can be executed remotely. There is not any exploit available. Upgrading the affected component is advised.

Detailsinfo

A vulnerability was found in Discourse up to 2026.1.1/2026.2.0 and classified as problematic. Affected by this issue is an unknown function of the component iFrame Handler. The manipulation with an unknown input leads to a cross site scripting vulnerability. Using CWE to declare the problem leads to CWE-80. The product receives input from an upstream component, but it does not neutralize or incorrectly neutralizes special characters such as "<", ">", and "&" that could be interpreted as web-scripting elements when they are sent to a downstream component that processes web pages. Impacted is integrity. CVE summarizes:

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.

The advisory is available at github.com. This vulnerability is handled as CVE-2026-27166 since 02/18/2026. The exploitation is known to be easy. The attack may be launched remotely. Successful exploitation requires user interaction by the victim. The technical details are unknown and an exploit is not available. This vulnerability is assigned to T1059.007 by the MITRE ATT&CK project.

Upgrading to version 2026.1.2, 2026.2.1 or 2026.3.0-latest.1 eliminates this vulnerability. Applying the patch c4762a4fac2f61f52f325396b11d3aeb955ea925 is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version.

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Productinfo

Type

Chat Software

Name

Discourse

Version

License

open-source

Website

Product: https://github.com/discourse/discourse/

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 4.3
VulDB Meta Temp Score: 4.3

VulDB Base Score: 3.5
VulDB Temp Score: 3.4
VulDB Vector: 🔒
VulDB Reliability: 🔍

NVD Base Score: 5.4
NVD Vector: 🔒

CNA Base Score: 4.1
CNA Vector (GitHub_M): 🔒

CVSSv2info

AV	AC	Au	C	I	A
💳	💳	💳	💳	💳	💳
💳	💳	💳	💳	💳	💳
💳	💳	💳	💳	💳	💳

Vector	Complexity	Authentication	Confidentiality	Integrity	Availability
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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Cross site scripting
CWE: CWE-80 / CWE-74 / CWE-707
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Yes

Availability: 🔒
Status: Not defined

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

0-Day	Unlock	Unlock	Unlock	Unlock
Today	Unlock	Unlock	Unlock	Unlock

Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: Discourse 2026.1.2/2026.2.1/2026.3.0-latest.1
Patch: c4762a4fac2f61f52f325396b11d3aeb955ea925

Timelineinfo

02/18/2026 CVE reserved
03/20/2026 +30 days Advisory disclosed
03/20/2026 +0 days VulDB entry created
03/25/2026 +5 days VulDB entry last update

Sourcesinfo

Product: github.com

Advisory: GHSA-h653-cq78-vjj2
Status: Confirmed

CVE: CVE-2026-27166 (🔒)
GCVE (CVE): GCVE-0-2026-27166
GCVE (VulDB): GCVE-100-351806

Entryinfo

Created: 03/20/2026 07:13
Updated: 03/25/2026 04:03
Changes: 03/20/2026 07:13 (67), 03/24/2026 08:57 (1), 03/25/2026 04:03 (11)
Complete: 🔍
Cache ID: 216::103