Authenticated URL redirection via encoded iframe traversal
Published Mar 19, 2026 · Updated Mar 19, 2026
HTML injection in Discourse before 2026.3.0-latest.1 allows remote authenticated users to redirect viewers through crafted posts. The PrettyText iframe sanitizer compares an encoded src path with allowed_iframes before decoding it, so %2e%2e traversal retains an allowed CodePen prefix while the browser resolves a prohibited URL. Exploitation requires permission to submit iframe-bearing content and a viewer who loads it; the reported consequence is navigation of the main page, not data disclosure or service interruption.
Summary
What happened
HTML injection in Discourse before 2026.3.0-latest.1 allows remote authenticated users to redirect viewers through crafted posts. The PrettyText iframe sanitizer compares an encoded src path with allowed_iframes before decoding it, so %2e%2e traversal retains an allowed CodePen prefix while the browser resolves a prohibited URL. Exploitation requires permission to submit iframe-bearing content and a viewer who loads it; the reported consequence is navigation of the main page, not data disclosure or service interruption.
The record
- CVE
- CVE-2026-27166
- Published
- Mar 19, 2026
- Updated
- Mar 19, 2026
- Vendor
- Discourse
- Product
- Discourse
- Classifications
- CWE-80
- Attack vector
- network
- Privileges
- authenticated
Timeline
How it unfolded
- Mar 19, 2026CVE publishedPublication date reported by the CVE source.
- Mar 19, 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, < 2026.1.2
- Affected versionversion=>= 2026.2.0-latest, < 2026.2.1
- Affected versionversion=< 2026.3.0-latest.1
What conditions does exploitation require?
What is affected?
Published CVSS scores
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.
Weakness, pattern, technique
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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