TS-2026-009: Insecure argument handling in Tailscale SSH permitted root access

tptacek•about 1 hour ago

This is such a venerable and ancient class of bugs, going at least as far back as AIX 3. Glad to see they're still makin' 'em like they used to.

(If you had SSH access to a host in your Tailscale ACL, you could log in as `-i` and get a root login.)

doublepg23•42 minutes ago

I’m a heavy Tailscale user, so I do trust them quite a bit, but I never used the Tailscale SSH feature. I feel like OpenSSH’s security record is pretty unbeatable, not sure why I’d swap over for such a security-sensitive tool.

dgacmu•7 minutes ago

I used it for a bunch of remote monitor boxes to have a way of centrally managing ssh access to things that were often on- and off-line. It was simple and convenient and access was easily revocable.

jdiff•32 minutes ago

I've used it before to access my tailnet machines through a browser on a machine I can't download software on.

bakies•18 minutes ago

Yeah pretty much just use tailscale as a vpn.. do one thing as they say.

isatty•32 minutes ago

Convenience for the most part but in general, I agree. I like having it as an option.

modeless•34 minutes ago

Tailscale SSH has caused me other problems in the past because it takes over port 22. I'm not a fan.

e40•about 1 hour ago

So, giving access via tailscale but using OpenSSH is safe, right?

lugoues•about 1 hour ago

Yes, this only involves their wrapper that is managed by ACL rules.

kbumsik•about 1 hour ago

Why own numbering instead of CVE?

vngzs•about 1 hour ago

It lets organizations (Tailscale) control the timing and narrative around the disclosure more directly. Organizations sometimes avoid the bureaucracy of going through CVE Numbering Authorities by self-publishing. Often a CVE assignment follows self-disclosure, especially when there's pressure to interoperate with vuln-scanning/compliance tooling

cyberax•about 1 hour ago

> "Tailscale SSH now rejects usernames with leading dashes."

Really? That's the fix?

A proper fix is to use "--" to separate arguments.

valleyer•23 minutes ago

A proper fix is not to shell out to a command at all; use getpwnam(3) or similar.

sedatk•about 1 hour ago

Their fix just future-proofs it in case the same bug gets reintroduced.

cyberax•20 minutes ago

This is just a dirty fix. It adds weird restrictions and masks issues.

Refactoring external invocations to use safe argument handling is a better way to fix it. Along with tests that exercise weird names.

sedatk•2 minutes ago

I argue the opposite: there’s no better fix for this. You can write the most elegant fix, whatever it is, and prevent that from happening only on the codebase that’s fixed. That doesn’t mean that the codebase will always be the only authority on authentication.

The username policy fixes this issue for good, regardless of whatever you write in the future, or whatever new mechanism is introduced.

It’s a restriction for sure, but it’s not a nonsense restriction? Who would have a username starting with a hyphen? I didn’t even know it was possible until today.

TS-2026-009: Insecure argument handling in Tailscale SSH permitted root access

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