---
cve: "CVE-2026-77164"
severity: "MEDIUM"
cvss: 6.2
epss: "0.1%"
vendor: "nextcloud"
kev: false
exploited: false
published: "2026-09-18 02:17:07"
tags: [cve, security, medium]
source: tsecurity.de CVE-Dossier
exported: "2026-09-22T08:04:57+02:00"
---

# CVE-2026-77164

> 6.2 MEDIUM

## Beschreibung

Circles' remote-instance signature verification fetches the attacker-supplied keyId URL before trust in the remote instance is established, and explicitly allows local/private addresses for this request, bypassing Nextcloud's core SSRF protections. The public, unauthenticated endpoints POST /apps/circles/event/ and POST /apps/circles/incoming/ reach this code path, allowing any unauthenticated user to force the server to issue a GET request to an internal address.

The response body of the internal request is never returned to the requester, so this is blind SSRF: an attacker can determine whether an internal service is reachable, but cannot read its response contents through this endpoint alone.

## CVSS-Vektor

```
CVSS:3.0/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
```

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

## Referenzen

- <https://hackerone.com/reports/3303283>

---
_Exportiert aus dem [tsecurity.de CVE-Dossier](https://tsecurity.de/cve?cve=CVE-2026-77164) · Datenquellen: EUVD (ENISA), NVD, OSV, CISA KEV, FIRST EPSS, Exploit-DB, BSI BITS_