CVE-2026-72728
Received Received - Intake

Onebox URL Bypass in Discourse

Publication date: 2026-08-10

Last updated on: 2026-08-10

Assigner: GitHub, Inc.

Description
Discourse is an open-source discussion platform. Prior to 2026.1.7, an authenticated user could submit specially formed URLs that bypassed the Onebox allowlist and embedded malicious content in a site. This issue is fixed in versions 2026.1.7, 2026.6.2, 2026.7.1, and 2026.8.0-latest.1.

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Meta Information

Published
2026-08-10
Last Modified
2026-08-10
Generated
2026-08-31
AI Q&A
2026-08-10
EPSS Evaluated
2026-08-29
NVD
CVE-2026-72728
EUVD
EUVD-2026-55667

Affected Vendors & Products

Showing 5 associated CPEs
Vendor Product Version / Range
discourse discourse 2026.1.7
discourse discourse 2026.6.2
discourse discourse 2026.7.1
discourse discourse 2026.8.0_latest.1
discourse discourse to 2026.1.7 (exc)

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-20 The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.

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Executive Summary

This vulnerability in Discourse, prior to versions 2026.1.7, 2026.6.2, 2026.7.1, and 2026.8.0-latest.1, allowed an authenticated user to submit specially crafted URLs that bypassed the Onebox allowlist. This could embed malicious content into a site, potentially leading to security risks.

Detection Guidance

To detect this vulnerability, check if your Discourse instance is running an affected version (2026.1.0-latest to before 2026.8.0-latest.1, 2026.7.1, 2026.6.2, or 2026.1.7). Review Onebox URL handling for improper iframe embeds or unauthorized domain bypasses. Inspect server logs for suspicious URL patterns or embedded content from untrusted sources.

Impact Analysis

An attacker could exploit this to inject malicious content into Discourse sites, potentially stealing user data, spreading malware, or defacing the site. Users with access to affected sites may unknowingly interact with harmful content.

Compliance Impact

This vulnerability allows authenticated users to embed malicious content via specially formed URLs, bypassing security restrictions. This could lead to data exfiltration or unauthorized access, which may violate GDPR (data protection) and HIPAA (health data security) requirements for access controls and data integrity.

Mitigation Strategies

Update Discourse to a patched version (2026.1.7, 2026.6.2, 2026.7.1, or 2026.8.0-latest.1) to fix the Onebox allowlist bypass issue.

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