CVE-2026-91134 — MEDIUM (5.4)

Vulnerability Description

Discourse is an open-source discussion platform. Prior to 2026.1.8, 2026.6.3, 2026.7.2, and 2026.8.0, the Discourse post sanitizer allowed a stored cross-origin iframe to bypass the allowed_iframes prefix policy when the iframe src contained encoded userinfo. The sanitizer validated a decoded form differently from the stored iframe src, allowing the browser to interpret an attacker-controlled host while the allowlist check accepted the encoded URL as an allowed prefix. An authenticated user with posting privileges could persist the iframe in a post and cause attacker-controlled cross-origin content to be rendered. This issue is fixed in versions 2026.1.8, 2026.6.3, 2026.7.2, and 2026.8.0.

CVSS Score

5.4

MEDIUM

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

Attack Vector

NETWORK

Attack Complexity

LOW

Privileges Required

LOW

User Interaction

NONE

Scope

UNCHANGED

Confidentiality

LOW

Integrity

LOW

Availability

NONE

Related Weaknesses (CWE)

CWE-20

References

FAQ

What is CVE-2026-91134?

CVE-2026-91134 is a vulnerability with a CVSS score of 5.4 (MEDIUM). Discourse is an open-source discussion platform. Prior to 2026.1.8, 2026.6.3, 2026.7.2, and 2026.8.0, the Discourse post sanitizer allowed a stored cross-origin iframe to bypass the allowed_iframes pr...

How severe is CVE-2026-91134?

CVE-2026-91134 has been rated MEDIUM with a CVSS base score of 5.4/10. Review the CVSS metrics above for detailed severity breakdown.

Is there a patch for CVE-2026-91134?

Check the references section above for vendor advisories and patch information. Review vendor security bulletins for remediation guidance.