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Tools/scripts/ftpmirror.py does not guard against arbitrary path constructions, and, given a connection to a malicious FTP server (or a man in the middle attack), it is possible that any file on the client's filesystem gets overwritten. Ie,. if we suppose that ftpmirror.py is run from a "base directory" /home/xxx/yyy, file creations can occur outside this base directory, such as in /tmp, /etc, /var, just to give some examples.
I've constructed a partial proof of concept FTP server that demonstrates directory and file creation outside the base directory (the directory the client script was launched from). I understand that most of the files in Tools/scripts/ are legacy applications that have long been deprecated. However, if the maintainers think these applications should be safe nonetheless, I'll be happy to construct and submit a patch that will remediate this issue.
Guido Vranken
Intelworks

I would guess that the most future-proof response to this would be to delete the script. If we do keep it, it should definitely be fixed.

New changeset 8f92ab37dd3a by Benjamin Peterson in branch '2.7':
delete old ftpmirror script, which now has security bugs (closes #23130)
https://hg.python.org/cpython/rev/8f92ab37dd3a
New changeset 223d0927e27d by Benjamin Peterson in branch '3.2':
delete old ftpmirror script, which now has security bugs (closes #23130)
https://hg.python.org/cpython/rev/223d0927e27d
New changeset e15d93926e47 by Benjamin Peterson in branch '3.3':
merge 3.2 (#23130)
https://hg.python.org/cpython/rev/e15d93926e47
New changeset 483746c32296 by Benjamin Peterson in branch '3.4':
merge 3.3 (#23130)
https://hg.python.org/cpython/rev/483746c32296
New changeset 4b64d300a67a by Benjamin Peterson in branch 'default':
merge 3.4 (#23130)
https://hg.python.org/cpython/rev/4b64d300a67a