---
cve: "CVE-2021-26918"
severity: "CRITICAL"
cvss: 9.8
epss: "2.6%"
vendor: "n/a"
kev: false
exploited: false
published: "2021-02-09 03:15:12"
tags: [cve, security, critical]
source: tsecurity.de CVE-Dossier
exported: "2026-10-10T10:50:33+02:00"
---

# CVE-2021-26918

> 9.8 CRITICAL · 🧪 PoC

## Beschreibung

The ProBot bot through 2021-02-08 for Discord might allow attackers to interfere with the intended purpose of the "Send an image when a user joins the server" feature (or possibly have unspecified other impact) because the uploader web service allows double extensions (such as .html.jpg) with the text/html content type. NOTE: there may not be cases in which an uploader web service is customer controlled; however, the nature of the issue has substantial interaction with customer controlled configuration. NOTE: the vendor states "This is just an uploader (like any other one) which uploads files to cloud storage and accepts various file types. There is no kind of vulnerability and it won't compromise either the client side or the server side.

## CISA-Anreicherung (vulnrichment/ADP)

- CISA-SSVC (Coordinator, v2.0.3):
  - Exploitation: **poc**
  - Automatable: **yes**
  - Technical Impact: **total**

## CVSS-Vektor

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

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

## Schwachstellen-Klasse

- **CWE-434** — Unrestricted Upload of File with Dangerous Type
  The product allows the upload or transfer of dangerous file types that are automatically processed within its environment.

## Angriffsmuster (CAPEC)

- [CAPEC-1 — Accessing Functionality Not Properly Constrained by ACLs](https://capec.mitre.org/data/definitions/1.html) _(Severity: High)_

## ATT&CK-Techniken

- [T1574.010 — Hijack Execution Flow: ServicesFile Permissions Weakness](https://attack.mitre.org/techniques/T1574/010/)

## Referenzen

- <https://raw.githubusercontent.com/TheLastVvV/Vulnerability-Reports-and-CVE/main/Reports/Discord%20Probot%20-%20Unrestricted%20File%20Upload.txt>
- <http://packetstormsecurity.com/files/161347/Discord-Probot-Arbitrary-File-Upload.html>

---
_Exportiert aus dem [tsecurity.de CVE-Dossier](https://tsecurity.de/sicherheitsluecken/cve-2021-26918/) · Datenquellen: EUVD (ENISA), NVD, OSV, CISA KEV, FIRST EPSS, Exploit-DB, BSI WID (CSAF)_