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Date: Wed, 3 Apr 2024 15:40:35 +0200
From: Matthias Gerstner <mgerstner@...e.de>
To: oss-security@...ts.openwall.com
Subject: dnf5daemon-server: Incomplete fix of CVE-2024-1929 (CVE-2024-2746)
Hello list,
CVE-2024-1929 that we previously reported [1] for the dnf5 D-Bus component has
not been completely fixed. This post deals with the remaining issue we
discovered.
We offer this report also as a rendered HTML version on our blog [8].
Unsafe Configuration Item "reposdir" in Whitelist
=================================================
The problem with CVE-2024-1929 was that the dnf5 D-Bus daemon accepted
arbitrary configuration parameters from unprivileged users, which allowed a
local root exploit by tricking the daemon into loading a user controlled
"plugin". All of this happened before Polkit authentication was even started.
The original bugfix [2] consists of a whitelist of configuration items, that
unprivileged users are allowed to override, when using the dnf5 D-Bus
interface. While checking each of the whitelisted items, we found that the
setting "reposdir" allows to specify the path to an arbitrary directory, in
which repository configuration files (`*.repo`) will be processed [3] by the
privileged dnf5 daemon.
The dnf5 library code does not check whether non-root users control the
directory in question. The code does check [4] for file type and filename
extension of contained files; it follows symlinks and is subject to a race
condition, however:
```
std::filesystem::directory_iterator di(dir_path, ec);
std::vector<std::filesystem::path> paths;
for (auto & dentry : di) {
auto & path = dentry.path();
if (dentry.is_regular_file() && path.extension() == ".repo") {
paths.push_back(path);
}
}
std::sort(paths.begin(), paths.end());
for (auto & path : paths) {
create_repos_from_file(path);
}
```
By the time the (checked) path is passed to `create_repos_from_file()`, the
user controlling the directory can replace it with an arbitrary other file or
symlink, thereby tricking the library to operate on arbitrary file types and
file paths.
On one hand, this poses a Denial-of-Service attack vector by making the daemon
operate on a blocking file (e.g. named FIFO special file) or a very large file
that causes an out-of-memory situation (e.g. /dev/zero). On the other hand,
this can be used to let the daemon process privileged files like /etc/shadow.
The file in question is parsed as an INI file. Error diagnostics resulting from
parsing privileged files could cause information leaks, if these diagnostics
are accessible to unprivileged users. In the case of libdnf5, no such user
accessible diagnostics should exist, though.
Even more interestingly, a local attacker can place a valid repository
configuration file in this directory. This configuration file allows to specify
a plethora of additional configuration options [5]. This makes various
additional code paths in libdnf5 accessible to the attacker. This, and the
possibility to configure arbitrary repositories, could very well allow further
privilege escalation, although we did not investigate more deeply if and how
this would be possible.
This follow-up issue confirms the sentiment expressed in our original report,
that one has to be extremely careful about feeding untrusted input into the
libdnf5 library, which is not designed to run in mixed security scope setups.
Bugfix and CVE Assignment
=========================
The bugfix [6] simply consists of the removal of the "reposdir" entry from the
whitelist of configuration items. Upstream release 5.1.17 [7] contains the
bugfix. The Red Hat security team assigned CVE-2024-2746 to track this
incomplete fix of CVE-2024-1929.
4) Discovery Process
====================
We noticed the incomplete fix only at a late time, when our openSUSE dnf5
package maintainer asked for the inclusion of the fixed package into openSUSE
Tumbleweed. It is unfortunate that this happened too late to prevent an
incomplete fix for CVE-2024-1929, and thus made a follow-up CVE assignment and
coordinated release process necessary.
Since the original issues had been handled as part of a coordinated disclosure
process, there should have been a review of the proposed patches before
publication. Due to the circumstances of an early publication of the fixes,
outside of the coordinated release process, there never was a defined point in
time for us to actually review them. We aim to avoid such situations in the
future by being more careful about reviewing patches, especially when no
straightforward coordinated release process can be established with upstream.
5) Timeline
===========
|2024-03-11|We reported the issue to secalert@...hat.com.|
|2024-03-13|The discussion for the issue was moved to a new group of contacts involving the dnf5 developers.|
|2024-03-20|One of the dnf5 developers confirmed the issue and suggested dropping "reposdir" from the whitelist.|
|2024-03-20|Red Hat security assigned CVE-2024-2746 for the follow-up issue.|
|2024-03-26|Discussions about the coordinated release date took place, 2024-04-02 has been mentioned.|
|2024-04-02|Red Hat security informed us that they actually had 2024-04-03 in mind.|
|2024-04-03|Upstream published release 5.1.17 containing the bugfix.|
6) References
=============
[1]: https://www.openwall.com/lists/oss-security/2024/03/04/2
[2]: https://github.com/rpm-software-management/dnf5/commit/6e51bf2f0d585ab661806076c1e428c6482ddf86
[3]: https://github.com/rpm-software-management/dnf5/blob/5.1.16/libdnf5/repo/repo_sack.cpp#L597
[4]: https://github.com/rpm-software-management/dnf5/blob/5.1.16/libdnf5/repo/repo_sack.cpp#L584
[5]: https://github.com/rpm-software-management/dnf5/blob/5.1.16/libdnf5/repo/config_repo.cpp#L96
[6]: https://github.com/rpm-software-management/dnf5/commit/07c5770482605ca78aaed41f7224d141c5980de4
[7]: https://github.com/rpm-software-management/dnf5/releases/tag/5.1.17
[8]: https://security.opensuse.org/2024/04/03/dnf5daemon-resposdir-followup.html
--
Matthias Gerstner <matthias.gerstner@...e.de>
Security Engineer
https://www.suse.com/security
GPG Key ID: 0x14C405C971923553
SUSE Software Solutions Germany GmbH
HRB 36809, AG Nürnberg
Geschäftsführer: Ivo Totev, Andrew McDonald, Werner Knoblich
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