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Mon, 20 Jul 2026 08:56:03 +0000 Date: Mon, 20 Jul 2026 10:56:02 +0200 From: Johannes Segitz To: selinux@vger.kernel.org Cc: Matthias Gerstner Subject: SELinux Userspace Utilities: Local Denial-of-Service Attack Vectors in seunshare in release 3.10 Message-ID: Precedence: bulk X-Mailing-List: selinux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="G135DQ0MmJfKZY1J" Content-Disposition: inline X-Spam-Flag: NO X-Spam-Score: -6.40 X-Spamd-Result: default: False [-6.40 / 50.00]; BAYES_HAM(-3.00)[100.00%]; SIGNED_PGP(-2.00)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; MIME_GOOD(-0.20)[multipart/signed,multipart/mixed,text/plain]; NEURAL_HAM_SHORT(-0.20)[-1.000]; FUZZY_RATELIMITED(0.00)[rspamd.com]; RCVD_TLS_ALL(0.00)[]; ARC_NA(0.00)[]; MISSING_XM_UA(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; MIME_TRACE(0.00)[0:+,1:+,2:+,3:~,4:~]; RCPT_COUNT_TWO(0.00)[2]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; TO_MATCH_ENVRCPT_ALL(0.00)[]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo,opensuse.org:url,suse.com:mid,suse.com:url,suse.de:email]; RCVD_COUNT_TWO(0.00)[2]; HAS_ATTACHMENT(0.00)[] X-Spam-Level: --G135DQ0MmJfKZY1J Content-Type: multipart/mixed; boundary="WcFHN6HtIvL3jPgt" Content-Disposition: inline --WcFHN6HtIvL3jPgt Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable In case you missed it on OSS ----- Forwarded message from Matthias Gerstner ----- Date: Wed, 15 Jul 2026 12:48:22 +0200 =46rom: Matthias Gerstner To: oss-security@lists.openwall.com Reply-To: oss-security@lists.openwall.com Subject: [oss-security] SELinux Userspace Utilities: Local Denial-of-Servic= e Attack Vectors in seunshare in release 3.10 Hello list, this is a report about Denial-of-Service issues in the `seunshare` setuid-root program. We also offer a rendered HTML version of this report on our blog [1]. Summary: seunshare is a setuid-root utility used for sandboxing untrusted applications based on Linux namespaces and SELinux policies. During a code review we identified two local Denial-of-Service attack vectors in version 3.10 of the utility. 1) Introduction =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D The `seunshare` program [2] is part of the SELinux [3] "sandbox" feature, which is used to confine untrusted programs using Linux mount namespaces and restrictive SELinux policies. The program is designed to be installed with setuid-root privileges, accessible to all users in the system. We have been asked to review the program's security [4] with the intention of assigning the setuid bit to it on SUSE distributions in the future. Fedora Linux already ships this program with setuid-root enabled; other SELinux-enabled Linux distributions may do so as well. During our review of the utility's code [5] in version 3.10 [6] of the SELinux userspace utilities we identified two local Denial-of-Service attack vectors, which will be described in detail in the following sections. Upstream independently fixed these issues in version 3.11 [7], without clearly marking them as security issues, however. The rest of this report is based on version 3.10 of the codebase of `seunshare`. 2) Design Overview =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D The `seunshare` program is relatively small, consisting of about 1,000 lines of C code. The elevated `root` privileges are primarily needed to setup a custom mount namespace for the sandbox environment. The program accepts a range of command line arguments which, among others, allow to request dedicated directories to be used for the following paths inside the sandbox: - the user's home directory. - the `/tmp` directory. - the `/run/user/` directory. For the `/run` and `/tmp` directories, the source paths specified by the user are copied into a random temporary directory in the initial mount namespace under `/tmp/.sandbox-