Magic Wormhole: "wormhole receive" allows arbitrary local file overwrite

Impact

What kind of vulnerability is it? Who is impacted?

Receiving a file (wormhole receive) from a malicious party could result in overwriting critical local files, including ~/.ssh/authorized_keys and .bashrc. This could be used to compromise the receiver's computer.

Only the sender of the file (the party who runs wormhole send) can mount the attack. Other parties (including the transit/relay servers) are excluded by the wormhole protocol.

Patches

Has the problem been patched? What versions should users upgrade to?

The bug has been fixed in magic-wormhole 0.23.0. All users should upgrade to this version.

The vulnerability first surfaced in the 0.21.0 release on 23-Oct-2025.

Workarounds

Is there a way for users to fix or remediate the vulnerability without upgrading?

As a workaround, the receiver can override the sender's filename with the --output or -o option. For example: wormhole receive -o shopping-list.txt will write the file to shopping-list.txt in the local directory, regardless of what the sender tries to do. To be effective, this option must be added to every invocation of wormhole receive / wormhole rx.

References

Are there any links users can visit to find out more?

Incoming file transfer requests include a filename, used to decide where the file contents will be written. Well-behaving senders compute this from the basename() of the sent file (which discards all but the last segment of the path). To guard against malicious senders, the receiver also applies basename() to the incoming filename. During refactoring in version 0.21.0, this receiver-side check was accidentally dropped. The check was restored in version 0.23.0 along with a unit test.

Many thanks to Ian McKenzie (@ikmckenz) for spotting the bug and reaching out with a fix.