External risk intelligence

Conduit Matrix Servers Allow Forged Membership Events

CVE advisorySeverity: CRITICAL (CVSS 9.9)

CVE-2025-68667

The vulnerability affects Matrix homeservers, which are designed to be public-facing network services that communicate via federation endpoints. These servers act as internet-accessible gateways for chat communications, and the flaw specifically targets unauthenticated federation API endpoints that are exposed by default in standard deployments to facilitate inter-server operation.

Denial of Service

Halo Surface Signal: 5 out of 5 — more likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

This vulnerability affects chat servers built on Matrix technology, allowing unauthenticated remote attackers to manipulate user accounts and room access. The core issue involves the server improperly validating the origin of requests, enabling attackers to force cryptographic signing of arbitrary membership events. This could lead to denial-of-service attacks, unauthorized removal of users, and potential exposure of confidential communication history in private rooms.

Attackers can force users out of chat rooms.
Leadership should remember to check if custom chat servers are affected.
Confirm if your organization uses this chat technology.

Attack Path

How an attacker could exploit the issue

An attacker can remotely target a chat server without authentication by sending specially crafted requests. This bypasses server-side validation, allowing the attacker to force the server to sign arbitrary membership events. When successful, this can lead to users being removed from chat rooms, including administrators, or an attacker joining private rooms by impersonating another user.

No authentication required.
Forge membership events via federation.
Room takeover and denial of service.

Live Threat

Current exploitation, exposure, and threat context

A remote attacker could force a chat server to cryptographically sign arbitrary membership events, enabling them to remove users from rooms or join private rooms. This could occur when the server fails to validate the origin of a signing request and the event's state key is a valid user ID on the target server. The impact depends on the attacker's ability to craft specific requests and the target server's configuration.

Server users and room states.
Forging cryptographic signing requests.
Denial of service or unauthorized room access.

Operational Fix

Recommended remediation, mitigation, and detection steps

For systems using Conduit or derived homeservers, platform and infrastructure teams are likely responsible for addressing this vulnerability. The first actionable step is to identify all instances of the affected technology, determine their exposure and criticality, locate the accountable system owner, and then prioritize remediation based on that assessment.

Platform/infrastructure teams own the issue.
Verify external exposure and business criticality first.
Plan remediation based on verified risk.

Supplementary metadata

CVSS vector

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Frequently asked questions

What is Conduit and the Matrix protocol?

Conduit is a lightweight homeserver software that implements the Matrix protocol, an open standard for secure, decentralized instant messaging. By using Matrix, these servers enable users to communicate across different platforms. Conduit and derived servers like Grapevine or tuwunel act as the core infrastructure hosting these chat rooms and user identities, managing the cryptographic signatures required to verify interactions within the decentralized network.

What does CVE-2025-68667 mean for my server?

This vulnerability involves improper input validation (CWE-20) and potentially unintended proxying or redirection (CWE-441). It allows an unauthenticated attacker to trick your server into cryptographically signing fraudulent membership events. Because the server fails to verify if a request legitimately originated from the claimed user, an attacker can effectively manipulate room membership, such as force-removing participants or joining private rooms without authorization.

How is this vulnerability triggered?

An attacker triggers this by sending malicious federation requests to your server. The flaw relies on the server trusting signing requests when the event's state key matches a user ID on your system. It is important to note that this does not require any prior authentication or special user access to execute. If the request meets the specific state key criteria, the server processes the event, resulting in unauthorized room actions.

Is my server at risk if it is internal only?

Halo Surface Signal indicates that this vulnerability is highly relevant for Matrix homeservers because they are designed to be public-facing gateways that communicate via federation endpoints. While internal-only deployments reduce the attack surface by limiting network accessibility, any server configured for standard Matrix federation is likely reachable by other servers. You should assume that federation services are intended to be accessible to the wider network.

How do I respond to this vulnerability?

First, audit your infrastructure to identify if you are running Conduit, continuwuity, Grapevine, or tuwunel. If you find affected versions, update to the patched releases identified in the project documentation. As an immediate temporary workaround, you can block access to the specific federation invite endpoint (`PUT /_matrix/federation/v2/invite/{roomId}/{eventId}`) at your reverse proxy to prevent exploitation while you prepare your upgrades.

References

Written by Nicholas Merritt

Nicholas Merritt is VP of Security Solutions at Halo Security. With more than 25 years across application security, vulnerability prioritization, and offensive security, he helps teams translate threat data into practical exposure validation and remediation focus. He authors Halo Threat Intelligence CVE advisories using Halo Surface Signal and H/A/L/O context to prioritize internet-facing risk.