CVE-2025-66488
Unknown Unknown - Not Provided
BaseFortify

Publication date: 2026-01-28

Last updated on: 2026-01-30

Assigner: GitHub, Inc.

Description
Discourse is an open source discussion platform. A vulnerability present in versions prior to 3.5.4, 2025.11.2, 2025.12.1, and 2026.1.0 affects anyone who uses S3 for uploads. While scripts may be executed, they will only be run in the context of the S3/CDN domain, with no site credentials. Versions 3.5.4, 2025.11.2, 2025.12.1, and 2026.1.0 fix the issue. As a workaround, disallow html or xml files for uploads in authorized_extensions. For existing html xml uploads, site owners can consider deleting them.
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Meta Information
Published
2026-01-28
Last Modified
2026-01-30
Generated
2026-06-16
AI Q&A
2026-01-29
EPSS Evaluated
2026-06-15
NVD
CVE-2025-66488
EUVD
EUVD-2025-206449
Affected Vendors & Products
Showing 4 associated CPEs
Vendor Product Version / Range
discourse discourse to 3.5.4 (exc)
discourse discourse From 2025.11.0 (inc) to 2025.11.2 (exc)
discourse discourse 2025.12.0
discourse discourse 2026.1.0
Helpful Resources
Exploitability
CWE
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KEV
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CWE ID Description
CWE-116 The product prepares a structured message for communication with another component, but encoding or escaping of the data is either missing or done incorrectly. As a result, the intended structure of the message is not preserved.
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Executive Summary

This vulnerability affects Discourse versions prior to 3.5.4, 2025.11.2, 2025.12.1, and 2026.1.0 when using S3 for uploads. It allows scripts to be executed, but only within the context of the S3/CDN domain and without access to site credentials. The issue can be mitigated by disallowing HTML or XML files for uploads or deleting existing HTML/XML uploads.

Impact Analysis

The vulnerability can lead to script execution in the S3/CDN domain context, which may result in limited integrity and availability impacts. However, since scripts run without site credentials, the risk to site security is reduced. The CVSS score indicates a moderate impact with potential for limited integrity and availability loss.

Detection Guidance

This vulnerability can be detected by checking if your Discourse installation is running a version prior to 3.5.4, 2025.11.2, 2025.12.1, or 2026.1.0 and if you are using S3 for uploads. Additionally, you can inspect your uploads for any html or xml files, which are vulnerable. Specific commands are not provided in the context.

Mitigation Strategies

Immediate mitigation steps include upgrading Discourse to version 3.5.4, 2025.11.2, 2025.12.1, or 2026.1.0. As a workaround, disallow html or xml files for uploads by configuring the authorized_extensions setting. For existing html or xml uploads, consider deleting those files.

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