---
cve: "CVE-2026-91134"
severity: "MEDIUM"
cvss: 5.4
epss: "0.2%"
vendor: "discourse"
kev: false
exploited: false
published: "2026-09-24 17:17:09"
tags: [cve, security, medium]
source: tsecurity.de CVE-Dossier
exported: "2026-10-01T21:13:22+02:00"
---

# CVE-2026-91134

> 5.4 MEDIUM · 🧪 PoC

## Beschreibung

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.

## CNA-Record (Kanon, cvelistV5)

- CNA: **GitHub_M**
- State: PUBLISHED
- Stand: 2026-09-29 02:56:30
- CNA-CVSS: **5.4** (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N`)

## CISA-Anreicherung (vulnrichment/ADP)

- CISA-SSVC (Coordinator, v2.0.3):
  - Exploitation: **none**
  - Automatable: **no**
  - Technical Impact: **partial**

## CVSS-Vektor

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

| Metrik | Wert | Bewertung |
|---|---|---|
| AV Angriffsvektor | Netzwerk | bad |
| AC Komplexität | Gering | bad |
| PR Privilegien | Gering | warn |
| UI Interaktion | Keine | bad |
| S Scope | Unverändert | good |
| C Vertraulichkeit | Gering | warn |
| I Integrität | Gering | warn |
| A Verfügbarkeit | Keine | good |

## Patch verfügbar (OSV)

- fb9247e04a826ab8e4d91168b3c4c839ec40bccc (Commit)
- 3ab62a8397926ed934b667a5db06284c45b4c774 (Commit)

## Referenzen

- <https://github.com/discourse/discourse/security/advisories/GHSA-54vw-chv3-wjpv>
- <https://github.com/discourse/discourse/pull/42882>
- <https://github.com/discourse/discourse/commit/0a8015e6c7a5079981843721494d30c9a91f5415>
- <https://github.com/discourse/discourse/commit/1304b0c04f87534053b0d574ae5a9b9ba13dd590>
- <https://github.com/discourse/discourse/commit/bac7dd1201911851462483271b4567246fa1309d>
- <https://github.com/discourse/discourse/commit/fed3a58c48412ce7207b72a4629ddbc44482cd64>

---
_Exportiert aus dem [tsecurity.de CVE-Dossier](https://tsecurity.de/cve?cve=CVE-2026-91134) · Datenquellen: EUVD (ENISA), NVD, OSV, CISA KEV, FIRST EPSS, Exploit-DB, BSI WID (CSAF)_