CVE-2026-77169

Executive Summary

CVE-2026-77169 is an improper authorization vulnerability (CWE-284) affecting the Nextcloud team folders (formerly group folders) app when combined with the workspace app. It allows API/REST-only delegated administrators to bypass folder-level authorization controls and access folders outside their granted permission scope. The vulnerability is scored CVSS 6.5 and, at the time of writing, remains unpatched with no public proof-of-concept or exploit code available.

Technical Analysis

CVE-2026-77169 is rooted in a failure to enforce authorization boundaries at the application layer. The affected software stack consists of two Nextcloud apps:

• team folders (formerly group folders) — provides shared, administratively-managed folder structures for organizations.
• workspace app — allows organizations to delegate limited administrative privileges for team folder management, but explicitly "via API/REST only," restricting those delegated administrators to folders for which they hold "advanced permissions."

The security control that fails is folder-level authorization. The intended design is that a delegated administrator provisioned through the workspace app should only be able to manage team folders within an explicitly granted permission set. Because the API/REST access path does not correctly validate that the acting administrator holds the required advanced permissions on the target folder, a delegated administrator can reach folders beyond their authorized scope.

Key characteristics of the flaw, as derivable from the description:

1. Attack vector is network (AV:N) — the bypass occurs through a remotely reachable API/REST interface.
2. Privileges required are high (PR:H) — the actor must already hold a delegated administrative role provisioned via the workspace app. This is not an unauthenticated flaw.
3. No user interaction (UI:N) — the bypass requires no action by a legitimate folder owner or victim.
4. Scope is unchanged (S:U) — the vulnerable component's authorization model is the sole boundary crossed.
5. Confidentiality and integrity are High (C:H/I:H), availability None (A:N) — successful abuse exposes folder contents the admin should not see and permits modification (management) of those folders, but does not directly cause a denial of service.

The vulnerability class is improper access control / broken object-level authorization (CWE-284). In practice, the API/REST surface performs coarse-grained checks (e.g., "is this caller a delegated administrator?") while failing to perform the fine-grained check ("does this caller have advanced permissions on this specific folder?"). The result is an authorization gap reachable only through the programmatic API rather than the web UI — which is consistent with the description restricting the delegated role to "API/REST only."

Important accuracy note: The NVD description does not disclose specific endpoint paths, request parameters, function names, or the exact code location responsible for the check. No implementation-level detail is available. The analysis above is limited to the vulnerability class (improper authorization) and the mechanism described by the CNA. No CVSS, EPSS, or PoC data beyond the fields provided should be inferred.

Exploitation Scenarios

No public PoC is available; the attack chain below is inferred strictly from the vulnerability class (improper authorization on an API/REST delegation path) and the description provided.

1) Reconnaissance / target identification An attacker first must already possess a delegated administrator account on a Nextcloud instance where the workspace app is used to delegate "team folder management via API/REST only." The attacker enumerates the instance's API/REST surface for team folder (formerly group folders) management operations — the same operations a delegated administrator is legitimately entitled to call, but scoped to a subset of folders. Target selection focuses on folder identifiers belonging to folders for which the attacker does not hold advanced permissions.

2) Triggering the flaw class The attacker authenticates to the API/REST interface with the delegated administrator credentials. The attacker then invokes a folder-management operation against a folder identifier outside their permission set. Because folder-level authorization is not enforced on the API path, the server processes the request as though the acting administrator were authorized for that folder — the object-level authorization check (the "does this principal have advanced permissions on this folder?" decision) is missing or incorrectly evaluated.

3) Execution method (vulnerability-class level) Execution is a direct REST/API request carrying a folder reference the caller should not be able to act upon. The bypass is purely an authorization logic failure — no injection, memory corruption, or credential theft is required. The delegated administrator's own valid credential is sufficient.

4) Post-exploitation impact On success, the delegated administrator gains read and manage access to folders beyond their granted scope. This yields unauthorized disclosure of shared team folder contents (confidentiality impact) and the ability to alter or manage those folders via API (integrity impact). Because the action uses a legitimate account through a legitimate interface, activity may blend with expected administrative traffic and evade naive detection. There is no direct availability impact.

Constraints: This attack cannot be performed by an unauthenticated user or a low-privileged regular user. It requires the victim organization to (a) run the team folders app, (b) run the workspace app, and (c) have provisioned at least one API/REST-only delegated administrator.

Impact Assessment

Successful exploitation grants a delegated administrator unauthorized access to and management capability over team folders outside their assigned permission set.

• Confidentiality (High): Unauthorized reading of shared folder contents, which may contain sensitive organizational documents, project data, or regulated information.
• Integrity (High): Unauthorized modification or management of folders the admin should not control, enabling tampering, re-sharing, or organizational structure manipulation.
• Availability (None): The flaw does not directly degrade service availability.

Blast radius is bounded by the delegated administrator's reach: only folders served by the affected team folders/workspace combination can be targeted, and only by principals who already hold a delegated administrative role. However, because delegated administrators are typically trusted internal or managed-service personnel, a malicious or compromised delegate can quietly widen their effective scope — undermining the entire premise of least-privilege delegation. In multi-tenant or managed-service deployments, this can cross intended organizational boundaries.

CVSS 6.5 (Medium) reflects a network-reachable, no-interaction flaw with high confidentiality and integrity impact, tempered by the high privilege requirement.

Detection Guidance

Sigma Rule

title: Nextcloud Team Folders Authorization Bypass via Workspace Delegated Admin API
id: 4f9c1b2a-7716-469a-9e3d-000000cve2026
status: experimental
description: Detects API/REST access to team folder (group folders) management endpoints by delegated administrators in patterns consistent with CVE-2026-77169 authorization bypass.
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-77169
author: Valters IT Threat Intelligence
date: 2026/01/01
logsource:
  product: nextcloud
  service: audit
detection:
  selection_app:
    appname:
      - 'groupfolders'
      - 'team_folders'
      - 'workspace'
  selection_action:
    action|contains:
      - 'folder'
      - 'mount'
      - 'acl'
      - 'permission'
  selection_api:
    method:
      - 'GET'
      - 'PUT'
      - 'POST'
      - 'DELETE'
  filter_legit:
    remote_user|endswith: '_service'
  condition: selection_app and selection_action and selection_api and not filter_legit
fields:
  - remote_user
  - appname
  - action
  - object_id
  - method
level: medium
tags:
  - attack.privilege_escalation
  - attack.t1078

YARA Rule

rule CVE_2026_77169_Nextcloud_TeamFolders_AuthzBypass
{
    meta:
        description = "Detects references to team folders / workspace delegation authorization handling in Nextcloud app server-side scripts, for CVE-2026-77169 review"
        author = "Valters IT Threat Intelligence"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-77169"
        date = "2026-01-01"
        severity = "medium"
    strings:
        $a = "groupfolders" ascii nocase
        $b = "team_folders" ascii nocase
        $c = "workspace" ascii nocase
        $d = "advanced permissions" ascii nocase
        $e = "delegated" ascii nocase
    condition:
        filesize < 2MB and
        (2 of ($a, $b, $c)) and
        1 of ($d, $e)
}

Suricata IDS Rule

alert http any any -> any any (msg:"CVE-2026-77169 Nextcloud Team Folders Delegated Admin Authorization Bypass Attempt"; flow:established,to_server; http.method; content:"PUT" or content:"POST" or content:"DELETE"; http.uri; content:"groupfolders"; nocase; http.uri; content:"/folders/"; nocase; http.header; content:"Authorization"; nocase; classtype:attempted-admin; sid:202677169; rev:1; metadata:created_at 2026_01_01, cve CVE-2026-77169, confidence low;)

Elastic Detection

sequence by user.name, source.ip with maxspan=5m
  [ authentication where event.action == "authentication_success" and user.name != null ]
  [ any where
      event.category == "web" and
      http.request.method in ("PUT", "POST", "DELETE") and
      stringContains(url.path, "groupfolders") and
      stringContains(url.path, "/folders/") ]

Splunk SPL Query

index=nextcloud sourcetype=nextcloud:audit
| search (app:"groupfolders" OR app:"team_folders" OR app:"workspace")
| search (action:*folder* OR action:*mount* OR action:*permission*)
| stats count min(_time) as first_seen max(_time) as last_seen values(action) as actions values(object_id) as targets
        by remote_user, client_ip
| where count > 5
| eval first_seen=strftime(first_seen,"%Y-%m-%d %H:%M:%S"), last_seen=strftime(last_seen,"%Y-%m-%d %H:%M:%S")
| sort - count

Wazuh OSSEC Rule

<group name="nextcloud,cve-2026-77169,">
  <rule id="100769" level="10">
    <decoded_as>json</decoded_as>
    <field name="app">groupfolders|team_folders|workspace</field>
    <field name="action">.*folder.*|.*mount.*|.*permission.*</field>
    <description>CVE-2026-77169: Possible Nextcloud team folders authorization bypass by delegated administrator</description>
    <mitre>
      <id>T1078</id>
    </mitre>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 0/4 — UNPATCHED. No patch evidence is available from any tracked source. The following guidance is precautionary and does not substitute for an official vendor fix if and when one is released.

1) Immediate mitigations

• Review and minimize the population of API/REST-only delegated administrators provisioned through the workspace app. Remove or restrict delegations that are not strictly required.
• Where feasible, temporarily disable the workspace app's delegated administration capability for team folder management until a fix is available, accepting the operational impact.
• Audit recent API/REST activity (folder mount, ACL, and permission operations) performed by delegated administrators for actions against folders outside their authorized scope.
• Enforce strong access logging and review of all team folder (group folders) API operations executed by delegated principals.
• Apply network or reverse-proxy rules to log and rate-limit API access to team folder management endpoints from delegated accounts.

2) Patch / upgrade steps

• No official patch is currently available. Monitor the Nextcloud security advisories and the team folders / workspace app release channels for an update addressing CVE-2026-77169.
• When a fixed release is published, validate the version in a staging environment, back up configuration and folder permissions, then upgrade the affected apps and redeploy.
• Re-verify folder-level authorization after upgrade by testing that a delegated administrator cannot reach a folder outside their advanced-permission set.

3) Long-term hardening

• Adopt least-privilege provisioning for delegated administrators; scope privileges to the narrowest set of folders.
• Implement periodic authorization reviews for all delegated roles across both the web UI and API/REST paths.
• Require defense-in-depth: alert on delegated administrators accessing folders outside their baseline, and correlate API actions with established behavior baselines.
• Track CWE-284-class issues in your software inventory and treat API-only administrative paths as a distinct, high-scrutiny attack surface.

References

• NVD — CVE-2026-77169: https://nvd.nist.gov/vuln/detail/CVE-2026-77169
• CWE-284: Improper Access Control — https://cwe.mitre.org/data/definitions/284.html
• Nextcloud Security Advisories — https://nextcloud.com/security/
• MITRE ATT&CK T1078 (Valid Accounts) — https://attack.mitre.org/techniques/T1078/
• CISA Known Exploited Vulnerabilities Catalog — https://www.cisa.gov/known-exploited-vulnerabilities-catalog (CVE-2026-77169 is not currently listed)

Threat actor / exploit-in-the-wild status: No public proof-of-concept, exploit code, or Nuclei template is available for CVE-2026-77169, and there is no evidence of exploitation in the wild or association with known threat actor campaigns as of this report. Patch confidence remains 0/4 (unpatched across all tracked sources).