Hostile iframe embedding via wildcard origin mismatch
Published Sep 24, 2026 · Updated Sep 24, 2026
Origin allowlist bypass in Discourse before 2026.1.8, 2026.6.3, 2026.7.2, and 2026.8.0 allows remote authenticated users to embed hostile iframes. The wildcard origin comparison accepts an allowlisted suffix after a URL authority separator, while browser parsing assigns the iframe to the preceding attacker-controlled origin. Exploitation requires posting privileges and a wildcard allowed_iframes pattern; rendered posts or Onebox oEmbed output can load attacker-controlled content.
Summary
What happened
Origin allowlist bypass in Discourse before 2026.1.8, 2026.6.3, 2026.7.2, and 2026.8.0 allows remote authenticated users to embed hostile iframes. The wildcard origin comparison accepts an allowlisted suffix after a URL authority separator, while browser parsing assigns the iframe to the preceding attacker-controlled origin. Exploitation requires posting privileges and a wildcard allowed_iframes pattern; rendered posts or Onebox oEmbed output can load attacker-controlled content.
The record
- CVE
- CVE-2026-91132
- Published
- Sep 24, 2026
- Updated
- Sep 24, 2026
- Vendor
- Discourse
- Product
- Discourse
- Classifications
- Unavailable
- Attack vector
- network
- Privileges
- authenticated
Timeline
How it unfolded
- Sep 24, 2026CVE publishedPublication date reported by the CVE source.
- Sep 24, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=>= 2026.1.0-latest, < 2026.1.8
- Affected versionversion=>= 2026.6.0-latest, < 2026.6.3
- Affected versionversion=>= 2026.7.0-latest, < 2026.7.2
- Affected versionversion=< 2026.8.0
What conditions does exploitation require?
What is affected?
Published CVSS scores
No CVSS assessment is available in this record.
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.
Activity data is delayed. The latest report is Sep 28, 2026.
Weakness, pattern, technique
No sourced classifications are available.
Public exploit references
No public exploit references are available in this record.
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Technologies
Your stack
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Your stack
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