Discourse: Stored oEmbed HTML injection via allowed iframe

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-91159
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-10-14 16:17:56 UTC
Updated2026-10-14 16:17:56 UTC
DescriptionDiscourse 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.

Risk And Classification

Primary CVSS: v3.1 7.7 HIGH from [email protected]

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:H/A:N

Problem Types: CWE-79 | CWE-79 CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary7.7HIGHCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:H/A:N
3.1CNADECLARED7.7HIGHCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:H/A:N

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Changed
Confidentiality
None
Integrity
High
Availability
None

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:H/A:N

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Discourse Discourse affected < 2026.1.9 Not specified
CNA Discourse Discourse affected >= 2026.7.0-latest, < 2026.7.3 Not specified
CNA Discourse Discourse affected >= 2026.8.0-latest, < 2026.8.1 Not specified
CNA Discourse Discourse affected >= 2026.9.0-latest, < 2026.9.0 Not specified

References

ReferenceSourceLinkTags
github.com/discourse/discourse/security/advisories/GHSA-f9jx-vv33-4282 [email protected] github.com
github.com/discourse/discourse/commit/ed6f83f123d1a4c6c6c7e64c8a2233e3cb... [email protected] github.com
github.com/discourse/discourse/commit/0953b31f5c2949d7d6ab5f6dc4c5e2f1b8... [email protected] github.com
github.com/discourse/discourse/commit/3fc2bad6cdca47b00958330d1ee612aa14... [email protected] github.com
github.com/discourse/discourse/commit/dde8bc4fb6200139f5eff7e100b0f3e829... [email protected] github.com
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