Stored Visual Overlay Vulnerability in Discourse Open-Source Discussion Platform
CVE-2026-91159

7.7HIGH

Key Information:

Vendor

Discourse
Status
Discourse
Vendor
CVE Published:
14 October 2026

What is CVE-2026-91159?

The vulnerability affects Discourse, an open-source discussion platform, where prior to specific versions, the oEmbed processing incorrectly trusted attacker-controlled HTML fragments. This allowed users with posting privileges to leverage allowlisted iframe sources and combine them with unrelated HTML or CSS content. Consequently, it enabled the attacker to create misleading or fraudulent user interfaces, potentially impacting content integrity. Fixes were implemented in versions 2026.9.0, 2026.8.1, 2026.7.3, and 2026.1.9.

Affected Version(s)

discourse < 2026.1.9 < 2026.1.9

discourse >= 2026.7.0-latest, < 2026.7.3 < 2026.7.0-latest, 2026.7.3

discourse >= 2026.8.0-latest, < 2026.8.1 < 2026.8.0-latest, 2026.8.1

References

https://github.com/discourse/discourse/security/advisorie...
x_refsource_CONFIRM
https://github.com/discourse/discourse/commit/0953b31f5c2...
x_refsource_MISC
https://github.com/discourse/discourse/commit/3fc2bad6cdc...
x_refsource_MISC

CVSS V3.1

Score:
7.7
Severity:
HIGH
Confidentiality:
None
Integrity:
High
Availability:
None
Attack Vector:
Network
Attack Complexity:
Low
Privileges Required:
Low
User Interaction:
None
Scope:
Changed

Timeline

  • Vulnerability published

  • Vulnerability Reserved

.