CVE-2022-41925

A vulnerability identified in the Tailscale client allows a malicious website to access the peer API, which can then be used to access Tailscale environment variables. In the Tailscale client, the peer API was vulnerable to DNS rebinding. This allowed an attacker-controlled website visited by the node to rebind DNS for the peer API to an attacker-controlled DNS server, and then making peer API requests in the client, including accessing the node’s Tailscale environment variables. An attacker with access to the peer API on a node could use that access to read the node’s environment variables, including any credentials or secrets stored in environment variables. This may include Tailscale authentication keys, which could then be used to add new nodes to the user’s tailnet. The peer API access could also be used to learn of other nodes in the tailnet or send files via Taildrop. All Tailscale clients prior to version v1.32.3 are affected. Upgrade to v1.32.3 or later to remediate the issue.

Weakness

The web application does not, or can not, sufficiently verify whether a well-formed, valid, consistent request was intentionally provided by the user who submitted the request.

Affected Software

Potential Mitigations

• Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
• For example, use anti-CSRF packages such as the OWASP CSRFGuard. [REF-330]
• Another example is the ESAPI Session Management control, which includes a component for CSRF. [REF-45]
• Use the “double-submitted cookie” method as described by Felten and Zeller:
• When a user visits a site, the site should generate a pseudorandom value and set it as a cookie on the user’s machine. The site should require every form submission to include this value as a form value and also as a cookie value. When a POST request is sent to the site, the request should only be considered valid if the form value and the cookie value are the same.
• Because of the same-origin policy, an attacker cannot read or modify the value stored in the cookie. To successfully submit a form on behalf of the user, the attacker would have to correctly guess the pseudorandom value. If the pseudorandom value is cryptographically strong, this will be prohibitively difficult.
• This technique requires Javascript, so it may not work for browsers that have Javascript disabled. [REF-331]

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/111.html
• https://cwe.mitre.org/data/definitions/462.html
• https://cwe.mitre.org/data/definitions/467.html
• https://cwe.mitre.org/data/definitions/62.html

References

• https://emily.id.au/tailscale
• https://github.com/tailscale/tailscale/security/advisories/GHSA-qccm-wmcq-pwr6
• https://tailscale.com/security-bulletins/#ts-2022-005