CVE-2026-91123

What it is

Discourse is an open-source discussion platform. Prior to 2026.1.8, 2026.6.3, 2026.7.2, and 2026.8.0, the iframe src traversal guard did not treat literal backslashes as path separators after decoded dot segments. A crafted source could therefore pass an allowed_iframes subpath check while browser URL normalization moved the iframe outside the intended allowed path. The resulting iframe could load content from a location that the administrator did not allow. This issue is fixed in versions 2026.1.8, 2026.6.3, 2026.7.2, and 2026.8.0.

At a glance

Exploitability

Can be exploited over the network without logging in. Limited direct impact.

Exploit odds

0.3% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2026-09-14 19:36 UTC ReservedThe CVE id was reserved by its CNA
2. 2026-09-24 17:17 UTC PublishedDisclosed publicly on CVE.org and NVD
3. 2026-09-24 18:19 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 0.3% in the next 30 days (EPSS).
• Severity: 7.2 HIGH (CVSS).
• Fix: a patch or advisory is linked.

Details

Published

2026-09-24 17:17 UTC

Last modified

2026-09-24 18:19 UTC

Exploit probability

0.3% · EPSS, next 30 days

Weakness

CWE-22 · Path traversal

Record status

Deferred

Attack profile CVSS 3.1 · 7.2

Attack vector

Network

Complexity

Low

Privileges needed

None

User interaction

None

Scope

Changed

Confidentiality

Low

Integrity

Low

Availability

None

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2026-91123.md and follow it. Check whether this project is affected by CVE-2026-91123. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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