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Bug 1639076 - (CVE-2018-15687) CVE-2018-15687 systemd: Dereference of symlinks in chown_recursive.c:chown_one() allows for modification of file privileges
CVE-2018-15687 systemd: Dereference of symlinks in chown_recursive.c:chown_on...
Status: NEW
Product: Security Response
Classification: Other
Component: vulnerability (Show other bugs)
unspecified
All Linux
medium Severity medium
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Assigned To: Red Hat Product Security
impact=moderate,public=20181026,repor...
: Security
Depends On: 1643367 1643368
Blocks: 1639078
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Reported: 2018-10-14 22:35 EDT by Sam Fowler
Modified: 2018-10-31 03:54 EDT (History)
25 users (show)

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Description Sam Fowler 2018-10-14 22:35:14 EDT 
systemd is vulnerable to improper dereference of symlinks in the core/chown_recursive.c:chown_one() function. An attacker with local access can exploit this via services with certain configurations to modify the file permissions of arbitrary files.
Comment 1 Riccardo Schirone 2018-10-22 03:18:52 EDT 
When using systemd's features CacheDirectory, LogsDirectory or StateDirectory together with the DynamicUser feature, systemd needs to recursively change ownership of those directories. While doing this, when the file is not a link the file mode is re-set to be sure the kernel doesn't change it (which could happen with SUID/SGID files), but an attacker may be able to bypass the link check and change the mode of any file in the filesystem.
Comment 2 Riccardo Schirone 2018-10-22 03:43:57 EDT 
Statement:

This issue did not affect the versions of systemd as shipped with Red Hat Enterprise Linux 7 as the vulnerable code was introduced in a newer version of the package.
Comment 3 Riccardo Schirone 2018-10-26 02:22:43 EDT 
Patch currently under review at:
https://github.com/systemd/systemd/pull/10517
Comment 4 Riccardo Schirone 2018-10-26 02:24:23 EDT 
Created systemd tracking bugs for this issue:

Affects: fedora-all [bug 1643367]
Comment 6 Riccardo Schirone 2018-10-29 03:02:35 EDT 
Acknowledgments:

Name: Ubuntu, Jann Horn (Google Project Zero)
Comment 7 Riccardo Schirone 2018-10-31 03:54:06 EDT 
Upstream patch:
https://github.com/systemd/systemd/commit/dc81f52c4d07de0c24f16edf889120780d9ae734
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