Malicious iframe embedding via prefix-matched origins
Published Aug 10, 2026 · Updated Aug 10, 2026
Improper input validation in Discourse Onebox before 2026.1.7 allows remote authenticated users to embed attacker-controlled iframes. Onebox::Engine.origins_to_regexes converted allowed origins into start-anchored regular expressions but omitted an authority boundary, so crafted URLs that merely prefix-matched an allowed origin passed validation. Remote authenticated users can submit oEmbed content whose iframe source uses an attacker-controlled authority, causing untrusted embedded content to be stored and displayed on the forum.
Summary
What happened
Improper input validation in Discourse Onebox before 2026.1.7 allows remote authenticated users to embed attacker-controlled iframes. Onebox::Engine.origins_to_regexes converted allowed origins into start-anchored regular expressions but omitted an authority boundary, so crafted URLs that merely prefix-matched an allowed origin passed validation. Remote authenticated users can submit oEmbed content whose iframe source uses an attacker-controlled authority, causing untrusted embedded content to be stored and displayed on the forum.
The record
- CVE
- CVE-2026-72728
- Published
- Aug 10, 2026
- Updated
- Aug 10, 2026
- Vendor
- Discourse
- Product
- Discourse
- Classifications
- CWE-20, T1190
- Attack vector
- network
- Privileges
- authenticated
Timeline
How it unfolded
- Aug 10, 2026CVE publishedPublication date reported by the CVE source.
- Aug 10, 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=< 2026.1.7
- Affected versionversion=>= 2026.6.0-latest, < 2026.6.2
- Affected versionversion=>= 2026.7.0-latest, < 2026.7.1
- Affected versionversion=>= 2026.8.0-latest, < 2026.8.0-latest.1
What conditions does exploitation require?
What is affected?
Published CVSS scores
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Attacks
What attackers are doing with it
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Public exploit references
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Technologies
Your stack
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Your stack
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