This bug was fixed in the package fscrypt - 0.2.2-0ubuntu2.1
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fscrypt (0.2.2-0ubuntu2.1) bionic-security; urgency=medium
* SECURITY UPDATE: Privilege escalation via improperly restored
supplementary groups in libpam-fscrypt (LP: #1787548)
- CVE-2018-6558.patch: Save the euid, egid, and supplementary groups when
entering the PAM module, drop privileges to perform actions on behalf of
the user, and then properly restore the saved values before exiting the
PAM module. Based on patch from upstream.
- CVE-2018-6558
* 0001-security-drop-and-regain-privileges-in-all-threads.patch: Drop and
regain privileges in all threads of the current process
* 0001-Ensure-keyring-privilege-changes-are-reversible.patch: Ensure keyring
privilege changes are reversible to prevent failures when, for example,
"su " is executed as an unprivileged user
-- Tyler Hicks Wed, 22 Aug 2018 18:57:26 +
** Changed in: fscrypt (Ubuntu)
Status: Confirmed => Fix Released
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https://bugs.launchpad.net/bugs/1787548
Title:
PAM fscrypt adds root(0) group to all users called by su
Status in Shadow:
Invalid
Status in fscrypt package in Ubuntu:
Fix Released
Status in shadow package in Ubuntu:
Invalid
Bug description:
related packages: /bin/su (from login , shadow)
OS: ubuntu 18.04.1, updated
Bug: a normal user (not in 'root' group), when the PAM module fscrypt
is active, all calls of su give the user additional group root(0).
Results: this is a permission escalation, such user can now delete
files owned by root group (where permisions are g+w)
Steps to reproduce:
0/ login uses pam unix authentication module (default on ubuntu, no action
needed)
0.1/ create a new user:
# useradd developer
1/ verify:
#id developer
// on my system, shows
// uid=1004(developer) gid=1004(developer) groups=1004(developer)
\su - developer -c id
sudo -u developer id
2/ enable pam-fscrypt
# apt install libpam-fscrypt
# pam-auth-update --enable fscrypt
3/ verify again (bug shows)
// repeate step 1/
// the su command will show the bug (sudo won't, interestingly)
\su - developer -c id
// uid=1004(developer) gid=1004(developer) groups=1004(developer),0(root)
4/ workaround and return to original state:
pam-auth-update --disable fscrypt
apt remove libpam-fscrypt
Thank you,
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