---
id: CVE-2026-77164
title: >-
  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 p…
summary: >-
  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 p…
severity: medium
cvss: 6.2
cvssVector: 'CVSS:3.0/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N'
cwe:
  - CWE-918
vendor: Nextcloud
product: Server
affected:
  - Server >= 31.0.0 <= 32.0.0
published: '2026-09-18'
updated: '2026-09-18'
sourceUpdated: '2026-09-18T20:17:22.273'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-77164'
references:
  - url: 'https://hackerone.com/reports/3303283'
    label: support@hackerone.com
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-77164.json
  - url: 'https://access.redhat.com/security/cve/CVE-2026-77164'
  - url: 'https://www.cve.org/CVERecord?id=CVE-2026-77164'
tags:
  - nvd
  - cve.org
  - csaf
  - vex
  - red-hat
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-09-18T19:40:57.953385Z'
epss: 0.00189
epssPercentile: 0.07506
ingestedAt: '2026-09-18T01:33:24.269Z'
scores:
  nvd: 6.2
  vendor: 5.3
---

## Overview

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.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

## Vendor advisories

- **Red Hat VEX** · updated 2026-09-23 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-77164.json)