High · published September 14, 2026
Description
The setuid-root `worker-launcher` binary adjusts ownership and permissions of worker directories by walking
the tree with FTS and calling `lchown` and `chmod` on each entry's full pathname while running with an
effective uid of 0. Both syscalls re-resolve the path at the time of the call, after FTS has classified the
entry, and the trees being walked are owned and writable by the untrusted topology user.
A tenant running code on a supervisor node could therefore replace an intermediate directory component with
a symbolic link between classification and the privileged operation, redirecting the root-owned `lchown` or
`chmod` at an arbitrary file on the host. The operation is repeatable at will, since crashing a worker
forces a relaunch and blob updates re-run the walk, so a failed attempt costs the attacker nothing.
This crosses the boundary that `supervisor.run.worker.as.user` and container isolation are intended to
enforce. It is the same defect class as the Hadoop container-executor issues from which this code derives.
Mitigation
Upgrade to 3.1.0, where the privileged walk operates on file descriptors it has already stat'd rather than
on pathnames re-resolved at call time.
Users who cannot upgrade immediately should not run untrusted topology code on supervisors configured with
`supervisor.run.worker.as.user`, since the launcher is the boundary being crossed. Note that the launcher
must be rebuilt and reinstalled after upgrading; replacing the Java artifacts alone is not sufficient.
Credit
The ASF -- found using Claude agents to study the security of open-source projects, validated and reported by Apache Storm.