CVE-2026-91159
Discourse: Stored oEmbed HTML injection via allowed iframe
- Published
- Oct 14, 2026
- Updated
- Oct 20, 2026
- Assigning CNA
- GitHub_M
- Evidence observed
- Nov 4, 2026
Primary CVSS
nvd · CVSS 3.1
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:H/A:NLow · next 30 days
- Percentile
- 36.2%
- Model date
- Nov 4, 2026
EPSS is a statistical estimate, not a certainty or a measure of impact. Combine it with CVSS, KEV status, exposure and your environment.
Summary
Discourse is an open-source discussion platform. Prior to 2026.9.0, 2026.8.1, 2026.7.3, and 2026.1.9, oEmbed processing treated an entire attacker-controlled HTML fragment as trusted when the fragment contained an iframe whose source matched the configured allowlist. A user with posting permission who controlled a public webpage and its oEmbed response could combine an allowlisted iframe with unrelated sibling HTML or CSS, causing stored visual overlays or other styled content to appear in post content and enabling misleading or fraudulent user interfaces. Exploitation requires a posting account, control of the fetched webpage and oEmbed response, and an allowlisted iframe source. The issue affects content integrity but does not expose restricted data, disrupt availability, or require interaction with Discourse Content Security Policy. This issue is fixed in versions 2026.9.0, 2026.8.1, 2026.7.3, and 2026.1.9.
Sources
Security PoC payload host for CVE-2026-91159 oEmbed test (authorized bug bounty)
Responsible use
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