CVE-2025-66488Network attack vector

Script execution via active S3 uploads

Published Jan 28, 2026 · Updated Jan 28, 2026

Cross-site scripting in affected Discourse releases allows remote authenticated users to run scripts through HTML or XML uploads. The advisory does not identify the code locus; it states that S3-backed uploads can preserve executable HTML or XML instead of rendering them inert. Exploitation requires S3 uploads, an allowed HTML or XML extension, and a user opening the file; execution stays on the S3/CDN origin without site credentials.

CVSS severity4.6
Medium
EPSS probability0.18%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Cross-site scripting in affected Discourse releases allows remote authenticated users to run scripts through HTML or XML uploads. The advisory does not identify the code locus; it states that S3-backed uploads can preserve executable HTML or XML instead of rendering them inert. Exploitation requires S3 uploads, an allowed HTML or XML extension, and a user opening the file; execution stays on the S3/CDN origin without site credentials.

The record

CVE
CVE-2025-66488
Published
Jan 28, 2026
Updated
Jan 28, 2026
Vendor
Discourse
Product
Discourse
Classifications
CWE-116, T1204.001
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Jan 28, 2026CVE publishedPublication date reported by the CVE source.
  2. Jan 28, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=>= 2025.11.0-latest, < 2025.11.2
  2. Affected versionversion=>= 2025.12.0-latest, < 2025.12.1
  3. Affected versionversion=>= 2026.1.0-latest, < 2026.1.0
  4. Affected versionversion=< 3.5.4

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Discourse · Discourseversion=>= 2025.11.0-latest, < 2025.11.2; version=>= 2025.12.0-latest, < 2025.12.1; version=>= 2026.1.0-latest, < 2026.1.0; version=< 3.5.4

Published CVSS scores

4.6GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:L/A:L
6.1NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-116Improper Encoding or Escaping of Output
T1204.001User Execution: Malicious Link

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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