CVE-2026-108839: thClaws through 0.141.0 Symlink Following File Write via POST /v1/inputs
thClaws through 0.141.0 contains a link-following vulnerability in the postinputs handler of the v1 API POST /v1/inputs endpoint that allows writes outside the workspace by following symlinks. Attackers who plant a symlink under the allowed inputs/ prefix can cause later authenticated uploads to write or truncate files outside the workspace with daemon privileges.
Affected Software
Event History
Frequently Asked Questions
Who can realistically exploit this issue?
An attacker must be able to plant a symlink beneath the allowed inputs/ prefix. Exploitation also depends on a later authenticated upload being sent to the POST /v1/inputs endpoint, so the attacker does not necessarily need to authenticate if they can induce or wait for another user or process to upload.
What is the impact of a successful exploit?
The upload can follow the planted symlink and write to or truncate a file outside the workspace. The write occurs with the daemon's privileges, so the reachable impact depends on which files that daemon account may modify.
How can I determine whether an installation is potentially affected?
Installations running thClaws through version 0.141.0 are potentially affected if untrusted parties can create symlinks under inputs/ and authenticated uploads use the v1 API POST /v1/inputs endpoint. Review that directory for symlinks and assess whether the daemon account can write to targets outside the workspace.
What can be done while patching is unavailable?
Prevent untrusted users or processes from creating entries, especially symlinks, under inputs/. Restrict access to the upload endpoint and ensure the thClaws daemon runs with only the minimum filesystem write permissions needed.