Unauthenticated API allows reading, writing to and deleting any user's private chat history on ████████

Bug reported by Juan Agustin Niccolini was disclosed at September 18, 2026, 6:04 am   |   Misconfiguration

An unauthenticated API was discovered that allowed reading, writing to, and deleting any user's private chat history on the organization's internal chatbot application. The API had no authentication mechanism in place, allowing an attacker to list all conversations, retrieve the complete message history of any conversation, create new conversations, and delete any conversation. The deletion of a conversation was incomplete, as the underlying messages remained retrievable even after the conversation was removed from the listing.

SSRF with bypass leads to client side hosting / vulnerabilities ( XSS and others )

Bug reported by Daniel Ferreira was disclosed at September 17, 2026, 10:54 pm   |   Server-Side Request Forgery (SSRF)

The web application was found to be vulnerable to server-side request forgery (SSRF). The SSRF vulnerability was discovered through testing with an HTTP interception proxy. The vulnerability allowed an attacker to make arbitrary HTTP requests from the server, which could potentially lead to unauthorized access or data exposure.

sign_multisig crashes monero-wallet-rpc on a malformed but decryptable multisig txset

Bug reported by 0xbro was disclosed at September 17, 2026, 5:45 pm   |  

The vulnerability in `monero-wallet-rpc`'s `sign_multisig` function allowed a malformed but decryptable multisig transaction set to cause a process crash instead of returning an error. The issue was resolved in version 0.18.5.0.

Restricted ZMQ RPC bypasses HTTP restricted-mode resource checks

Bug reported by 0xbro was disclosed at September 17, 2026, 5:42 pm   |  

The restricted ZMQ RPC in monerod did not enforce the same request restrictions as the restricted HTTP RPC. The ZMQ RPC relied primarily on a small method blocklist, allowing several allowed methods to accept requests that the restricted HTTP RPC explicitly rejected or capped. This issue was resolved in version 0.18.5.0.

ZMQ get_output_distribution duplicate amount DoS

Bug reported by 0xbro was disclosed at September 17, 2026, 5:38 pm   |  

The ZMQ `get_output_distribution` RPC was vulnerable to a memory exhaustion denial-of-service attack. The method accepted an unbounded `amounts` array and returned a separate distribution for each entry, allowing a small request to expand into a very large response by repeatedly including the amount `0`. The issue was also reachable with `--restricted-zmq-rpc` because ZMQ lacked the stricter validation applied by restricted HTTP RPC. The vulnerability was resolved in You are not allowed to view links. Register or Login to view. and v0.18.5.0.

Cross-User Lock/Unlock via Absolute DAV Path

Bug reported by Balvant Chavda was disclosed at September 17, 2026, 1:09 pm   |   Improper Authentication - Generic

A vulnerability was discovered in the files_lock app for Nextcloud. The vulnerability allowed any authenticated user to lock or unlock files they did not own by targeting absolute WebDAV paths of other users. This was possible because the DAV plugin resolved files from the absolute request URI without verifying that the user ID path segment matched the authenticated session user. This enabled cross-user manual locks and lock token disclosure, which allowed unauthorized callers to remove token-based locks of other users.

Shared smart albums in the Photos app can expose files outside the album owner's configured source folders

Bug reported by Joseph Semaan was disclosed at September 17, 2026, 10:48 am   |   Improper Access Control - Generic

A vulnerability was discovered in a file manager component of a file sharing application. The vulnerability allowed an attacker to access files outside of the intended shared folder by configuring more permissive search paths than the victim intended. This resulted in unauthorized information disclosure, as the system used the attacker's configuration to determine the search scope in the victim's folder. The vulnerability was caused by insufficient validation of the search paths provided by the attacker.

Critical broken access control: API-only delegated admin can enumerate all Team Folders and grant access to arbitrary groups

Bug reported by qloo was disclosed at September 17, 2026, 10:41 am   |   Improper Access Control - Generic

A critical broken access control vulnerability was discovered in Nextcloud's Group Folders app. The vulnerability allowed an API/REST only delegated admin to bypass folder-level authorization and gain access to any Team Folder by abusing the POST /index.php/apps/groupfolders/folders/{id}/groups endpoint. This was possible because the folder IDs were predictable, allowing the attacker to enumerate all Team Folders and mass-assign their own group, resulting in full access to organization-wide data.

Approval app's file-freshness check can be bypassed by omitting the etag parameter, allowing approval of unreviewed file changes

Bug reported by Dang Hung Vi was disclosed at September 17, 2026, 10:34 am   |   Business Logic Errors

A vulnerability was discovered in the approval app's file-freshness check. The vulnerability allowed bypassing the check by omitting the etag parameter, enabling approval of unreviewed file changes. This broke the integrity of the approval process, as the approver could approve a different file state than the one they reviewed.

Arbitrary Board Preference Injection via Deck Config API

Bug reported by Dang Hung Vi was disclosed at September 17, 2026, 10:20 am   |   Improper Access Control - Generic

A vulnerability was discovered in the Deck Config API of the Nextcloud application that allowed authenticated users to set board-scoped configuration keys for arbitrary board IDs without validating the user's ownership or permission to manage the referenced board.

Public collectives allow to create pages

Bug reported by _dha was disclosed at September 17, 2026, 10:16 am   |   Improper Access Control - Generic

A vulnerability was discovered in the Nextcloud Collectives application that allowed non-members accessing a public collective to create new pages through the backend API, bypassing the collective-level permission settings configured to restrict editing to administrators only. The vulnerability was caused by inconsistent permission enforcement between the user interface, collective settings, and backend API.

Unauthenticated blind SSRF in Circles signature verification bypasses Nextcloud local-address protections

Bug reported by Balvant Chavda was disclosed at September 17, 2026, 6:22 am   |   Server-Side Request Forgery (SSRF)

A blind SSRF vulnerability was discovered in the Circles app for Nextcloud. The vulnerability allowed unauthenticated users to force the server to fetch internal URLs, bypassing local-address protections in Nextcloud. The vulnerability was caused by the Circles app's signature verification process, which fetched an attacker-provided URL before trust was established.

Team membership information returned on API level based on ID

Bug reported by Melanie was disclosed at September 17, 2026, 5:49 am   |   Insecure Direct Object Reference (IDOR)

A vulnerability was discovered in the Nextcloud Circles app that allowed any authenticated user to access membership information for any circle and user combination, regardless of their authorization. The issue stemmed from a lack of permission checks in the affected service and request classes, as well as the public exposure of the vulnerable functionality through an API endpoint. This vulnerability could have led to the disclosure of sensitive organizational data, including private circle memberships, inheritance relationships, and user identification details.