CVE-2026-91159
Discourse: Stored oEmbed HTML injection via allowed iframe
Description
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.
INFO
Published Date :
Oct. 14, 2026, 4:17 p.m.
Last Modified :
Oct. 14, 2026, 4:17 p.m.
Remotely Exploit :
Yes !
Source :
[email protected]
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS 3.1 | HIGH | MITRE-CVE | ||||
| CVSS 3.1 | HIGH | [email protected] |
Solution
- Update Discourse to version 2026.9.0 or later.
- Apply specific patches for versions 2026.8.1, 2026.7.3, or 2026.1.9.
- Review and update oEmbed allowlist configuration.
- Validate processed HTML content for security.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-91159.
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-91159 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-91159
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-91159 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-91159 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
New CVE Received by [email protected]
Oct. 14, 2026
Action Type Old Value New Value Added Description 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. Added CVSS V3.1 AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:H/A:N Added CWE CWE-79 Added Affected New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/91xxx/CVE-2026-91159.json">CVE-2026-91159</a> Added Reference https://github.com/discourse/discourse/commit/0953b31f5c2949d7d6ab5f6dc4c5e2f1b8bf0b22 Added Reference https://github.com/discourse/discourse/commit/3fc2bad6cdca47b00958330d1ee612aa141b039a Added Reference https://github.com/discourse/discourse/commit/dde8bc4fb6200139f5eff7e100b0f3e829d37ab3 Added Reference https://github.com/discourse/discourse/commit/ed6f83f123d1a4c6c6c7e64c8a2233e3cb6a28d7 Added Reference https://github.com/discourse/discourse/security/advisories/GHSA-f9jx-vv33-4282