Security Bulletins

Description: An issue in the Tailscale coordination server in device reauthentication logic caused previously authenticated and tagged devices to lose their ACL tags upon reauthentication.

What happened?

The logic that handles the reauthentication to a new identity on an already-authenticated device with tags had a bug: instead of updating the device’s logged-in identity to the newly authenticated user, the device’s identity became that of the user who originally added it to the tailnet, without any tags.

The bug was introduced on 2022-10-26, and discovered and remediated on 2023-04-21. The bug was discovered when troubleshooting a user-reported issue.

Who is affected?

189 tailnets triggered this bug in the course of normal use of Tailscale, either directly by explicitly re-authenticating a device, or indirectly by using fast user switching to switch between multiple tailnets.

We have notified affected organizations where we have security contacts.

What is the impact?

Devices that encountered the bug had their tags removed, which reverted the device’s identity to that of the user who originally authenticated the device, or the owner of the auth key that was originally used to authenticate the device. In either case, this is the user listed as “Creator” in the Machines tab of the admin panel. Depending on access rules in the tailnet policy file, this could change the device’s network permissions.

We have analyzed the audit logs for affected tailnets, and found no evidence of deliberate exploitation. In most instances, device owners noticed the incorrect outcome of reauthentication, and corrected the device’s state themselves.

What do I need to do?

If you were not contacted by Tailscale, no action is required.  If you were contacted by Tailscale, reapply the desired tags to affected devices in the admin console, or by reauthenticating the devices. Tailscale has deployed a fix to the coordination server as of 2023-04-21, and notified affected organizations.

Description: An issue in the Tailscale coordination server allowed tailnets created by GitHub organizations which were subsequently renamed to be associated with a new GitHub organization with the previous name.

What happened?

Tailscale mapped tailnets created by GitHub organizations to their organization name, rather than to their organization ID. This meant that if a GitHub organization was renamed, and the previous name taken over by a new GitHub organization, the existing tailnet would be tied to the new GitHub organization instead of the original one.

Who is affected?

Up to 1,305 tailnets created by GitHub organizations may have been affected, if those GitHub organizations were renamed between 2021-06-18 and 2023-03-30 and fully relinquished the old GitHub organization name. Additional tailnets created by GitHub organizations could be verified to definitely not have been renamed in that time period based on organization membership.

No tailnets were definitively found to have been affected. If a tailnet created by a GitHub organization is affected, we can detect this the next time an unauthorized user logs in to the tailnet belonging to the renamed organization and block their access. We will contact the security contact for that tailnet if that happens.

What is the impact?

A renamed GitHub organization may have had their previous tailnet visible to a newly created GitHub organization with the same name. The new GitHub organization would be aware of the existence of the previous tailnet. Devices added to the new GitHub organization would be aware of the existence and some metadata of previous added devices, including: their host names, their OS and version, when the devices were last connected, and their public IP addresses. They would have been able to connect to these devices if allowed by ACLs. The new GitHub organization would not have had any admin access or be able to see or modify any setting in the admin console.

There is no evidence of this vulnerability being purposefully triggered or exploited.

What do I need to do?

No action is required. Tailscale has deployed a fix to the coordination server as of 2023-03-30.

GitHub organizations which were previously renamed and lost access to their tailnet should contact support. When renaming a GitHub organization, contact support to migrate the tailnet to the new GitHub organization.

Credits

We would like to thank Thomas Way for reporting this issue.

Reference: CVE-2023-28436

Severity: Medium

CVSS vector string: CVSS:3.0/AV:A/AC:L/PR:H/UI:R/S:C/C:H/I:N/A:N

Description: A vulnerability identified in the implementation of Tailscale SSH in FreeBSD allowed commands to be run with a higher privilege group ID than that specified by Tailscale SSH access rules.

Affected platforms: FreeBSD

Patched Tailscale client versions: v1.38.2 or later

What happened?

A difference in the behavior of the FreeBSD setgroups system call from POSIX meant that the Tailscale client running on a FreeBSD-based operating system did not appropriately restrict groups on the host when using Tailscale SSH. When accessing a FreeBSD host over Tailscale SSH, the egid of the tailscaled process was used instead of that of the user specified in Tailscale SSH access rules.

Who is affected?

9 tailnets with 22 FreeBSD nodes running Tailscale SSH since Tailscale v1.34 (released on 2022-12-04) may have had Tailscale SSH sessions with a higher privilege group ID than that specified in Tailscale SSH access rules.

We have notified affected organizations where we have security contacts.

What is the impact?

Tailscale SSH commands may have been run with a higher privilege group ID than that specified in Tailscale SSH access rules if they met all of the following criteria:

• The destination node was a FreeBSD device with Tailscale SSH enabled;
• Tailscale SSH access rules permitted access for non-root users; and
• A non-interactive SSH session was used.

What do I need to do?

If you are running Tailscale on FreeBSD, upgrade to v1.38.2 or later to remediate the issue. Admins of a tailnet can view FreeBSD nodes with unpatched versions in the admin console.

To update the local ports tree in advance of what’s available upstream, you can:

1. cd /usr/ports/security/tailscale
2. edit the Makefile to set PORTVERSION to 1.38.2
3. make makesum
4. make install

Tailscale SSH on other platforms is not affected.

Credits

We would like to thank Ryan Belgrave for reporting this issue.

Description: An issue in the Tailscale coordination server allowed nodes with expired node keys to continue communicating with other nodes in a tailnet.

What happened?

There was a flaw in Tailscale’s logic for expiring node keys. If the set of nodes that can connect in a tailnet (the netmap) didn’t have any changes, then expired node keys were not immediately removed from the netmap. The longest delay in removal was 19 days, from 2022-12-20 to 2023-01-09.

Who is affected?

All tailnets with nodes whose node keys expired prior to 2023-01-12 may have been affected. Admins of a tailnet can view nodes with expired node keys in the admin console.

What is the impact?

Connections between nodes could continue after a node key expired, both when the expired node key was the source or when it was the destination of a connection. Connections to nodes with expired node keys would only be possible if they met all of the following criteria:

• The peer node was in the same tailnet as, or shared into a tailnet with the node with the expired node key;
• The peer node and the node with the expired node key were allowed to connect based on the access rules in the tailnet policy file at the time of expiry of the node key;
• The tailnet’s netmap, including access rules, nodes added or removed from the tailnet, or connectivity of nodes in the tailnet did not change since the node key expiry; and
• Tailscale had not deployed a change to the coordination server since the node key expiry.

What do I need to do?

No action is required. Tailscale has deployed a fix to the coordination server as of 2023-01-11.

Upgrade clients to v1.36 or later for an additional mitigation. In conjunction with the coordination server fix, this mitigation prevents nodes from connecting to nodes with expired node keys if the Tailscale coordination server is offline or unreachable.

Credits

We would like to thank Derek Ellis and Alex Eiser for reporting this issue.

Description: An issue in the Tailscale coordination server allowed a malicious individual to share nodes from other tailnets to themselves, if they knew the node ID of the target.

What happened?

A bug in Tailscale’s node sharing logic allowed the creation of sharing invitations by unauthorized users. A malicious individual who knew a target node’s database ID could generate and accept a sharing invite for that node without being an admin of the target node’s tailnet.

This was possible for any node in any tailnet, as long as the individual knew the target’s node ID. The node ID is an integer used in the admin panel’s database, and is not related to the node “StableID” that is visible to Tailscale clients. A node’s ID is only visible in the API or admin console, by admins of either the node’s tailnet or a tailnet to which that node has already been shared. IDs are random 64-bit numbers that are not sequential or otherwise easily guessable.

The bug was introduced on 2022-09-14, reported to us on 2023-01-11, and remediated on 2023-01-12.

Who is affected?

All tailnets with nodes are affected.

What is the impact?

This vulnerability was not triggered or exploited. Analysis of tailnet logs shows that no unauthorized shares were created or accepted while the vulnerability was present, except as part of the proof of concept from the individual who reported the vulnerability.

Admins of a tailnet can review nodes that are shared out of their tailnet in the admin console. Sharing invites are logged as events in configuration audit logs. Admins can also review invites created and accepted in their configuration audit logs in the admin console.

What do I need to do?

No action is required. Tailscale has deployed a fix to the coordination server as of 2023-01-12, and verified that the vulnerability was not exploited.

Credits

We would like to thank Benjamin Roberts (tsujamin) for reporting this issue.

Reference: CVE-2022-41924

Severity: Critical

CVSS vector string: CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:L/A:H

Description: A vulnerability identified in the Tailscale Windows client allows a malicious website to reconfigure the Tailscale daemon tailscaled, which can then be used to remotely execute code.

Affected platforms: Windows

Patched Tailscale client versions: v1.32.3 or later, v1.33.257 or later (unstable)

What happened?

In the Tailscale Windows client, the local API was bound to a local TCP socket, and communicated with the Windows client GUI in cleartext with no Host header verification. This allowed an attacker-controlled website visited by the node to rebind DNS to an attacker-controlled DNS server, and then make local API requests in the client, including changing the coordination server to an attacker-controlled coordination server.

Who is affected?

All Windows clients prior to version v1.32.3 are affected.

What is the impact?

An attacker-controlled coordination server can send malicious URL responses to the client, including pushing executables or installing an SMB share. These allow the attacker to remotely execute code on the node.

Reviewing all logs confirms this vulnerability was not triggered or exploited.

What do I need to do?

If you are running Tailscale on Windows, upgrade to v1.32.3 or later to remediate the issue.

Credits

We would like to thank Emily Trau and Jamie McClymont (CyberCX) for reporting this issue. Further detail is available in their blog post.

Description: An issue in Tailscale’s implementation of the OAuth authentication flow for GitHub allowed users who authenticate to Tailscale with their GitHub user identity to create a tailnet for a GitHub organization using SAML authentication in GitHub Enterprise Cloud, where Tailscale is not an authorized OAuth app for their organization.

What happened?

Tailscale silently ignored a 403 error to the GitHub API query for organizations for an authenticated user that was returned when a user authenticated to SAML, but the organization had not authorized Tailscale. This only applied to organizations using SAML on GitHub Enterprise Cloud with OAuth app authorization enabled, and where Tailscale was not authorized.

As a result, a user identity could bypass the organization’s OAuth app access restrictions, and create a tailnet for the GitHub organization.

Who is affected?

Up to 7 tailnets for GitHub organizations on GitHub Enterprise Cloud which use SAML for authentication may have been created between 2021-06-18 and 2022-06-03 without Tailscale being an authorized OAuth app for their GitHub organization, and could have used Tailscale to connect devices in that organization. An additional 10 tailnets were created with no or only one device, and so could not have used Tailscale to connect between devices.

We have notified the Tailscale admins for the affected organizations who we were able to identify. We do not have a way to notify the GitHub organization owners.

If you’re a GitHub organization owner, you can see if Tailscale is approved for your GitHub organization by going to the organization’s settings page and selecting “Third-party access” from the left-hand navigation. Or, for an organization $your-org, navigate to

https://github.com/organizations/$your-org/settings/oauth_application_policy

What is the impact?

A tailnet may have been created for a GitHub organization without their GitHub organization owner’s approval. In this case, the use of Tailscale and the creation of a tailnet could be perceived as being sanctioned by their organization when it might not have been.

What do I need to do?

If you are affected, you will need to re-authenticate to keep using your tailnet. Tailscale has expired all admin console sessions for potentially affected GitHub organizations as of 2022-06-13. As a result, users in a potentially affected tailnet will need to re-authenticate the next time they access the admin console, and will not be able to do so without Tailscale being an authorized OAuth app, which may first require getting approval from their GitHub organization owner. Nodes in a potentially affected tailnet will also need to re-authenticate when their node keys expire. If you’re a GitHub organization owner, you can approve Tailscale as an OAuth app by following GitHub’s instructions for Approving OAuth Apps for your organization.

Tailscale has deployed a fix to the coordination server as of 2022-06-03, so that no new tailnets can be created without a GitHub organization owner’s approval.

Credits

We would like to thank Aurelia for reporting the issue. Further detail is available in their blog post.

Description: An issue in the Tailscale coordination server allowed individuals creating a new Tailscale account with a gmail.com email address to join the same tailnet, rather than individual tailnets.

What happened?

There was a flaw in Tailscale’s logic for migrating accounts between identity providers, and a new gmail.com shared tailnet was accidentally created. Once created, any user who tried to create a new Tailscale account with a gmail.com email address joined the shared gmail.com tailnet.

Who is affected?

A total of 44 users with 59 devices who created accounts for their gmail.com email addresses on 2022-05-11 between 10:56 and 13:12 PT were affected. We have notified affected users.

What is the impact?

Six connections between devices belonging to different users were made, but no traffic of concern flowed between them. Four connections were pings, and two connections were UDP traffic on port 27036, likely automated broadcasting by a gaming platform to discover peers to play with. There is no evidence of malicious traffic.

Impacted users could see some metadata about other users and devices from their devices’ clients, including users’ names, devices’ host names, and devices’ Tailscale IP addresses. This information was viewed by at least one user, who reported it to us.

One user, the tailnet Admin, was able to see all users and devices added to the shared gmail.com tailnet. This includes users’ email addresses, names, and when they were last connected; and devices’ host names, their OS and version, when the devices were last connected, and their public IP addresses. This information was viewed by the user, who reported it to us.

What do I need to do?

No action is required. Tailscale has deployed a fix to the coordination server as of 2022-05-11 13:12 PT.

New users registering for a Tailscale account with a gmail.com email address will create a tailnet as normal.

Credits

We would like to thank David Swafford and George Constantinides for reporting the issue.

Description: An issue in the Tailscale coordination server allowed individuals using GitHub to authenticate to Tailscale to have their devices join a tailnet associated with an empty GitHub username.

What happened?

There was a flaw in Tailscale’s authorization logic for the GitHub identity provider. If a user tried to authenticate to Tailscale using their GitHub identity, and GitHub returned a 500 error, then in some cases, Tailscale interpreted that as authorization for an empty GitHub username, and connected these devices to the tailnet associated with the empty GitHub username.

Who is affected?

A total of five devices belonging to four users were affected between 2021-06-15 and 2022-02-04, when the issue was reported and remediated. We have contacted the two users we were able to identify.

You may be affected if you authenticated to Tailscale using a GitHub account, and after authorizing a connection using GitHub, you received a connection error. Without being asked to select which GitHub user or organization tailnet to connect to, your device would have connected to a tailnet.

What is the impact?

No device connected to another device in the tailnet. Other than the two devices which belonged to the same user, no two devices in the tailnet had valid node keys at the same time, and so did not and would not have been able to establish connections.

A device’s existence and some metadata was shared with devices added later in time. Devices added later in time were able to see previously added devices, including: their host names, their OS and version, when the devices were last connected, and their public IP addresses.

There is no evidence of this vulnerability being purposefully triggered or exploited.

Credits

We would like to thank Marvin Boothby (boothb) for reporting the issue.