It was discovered that a systemd service that uses DynamicUser property can create a SUID/SGID binary that would be allowed to run as the transient service UID/GID even after the service is terminated. A local attacker may use this flaw to access resources that will be owned by a potentially different service in the future, when the UID/GID will be recycled.
A compromised or malicious service that uses DynamicUser property could leave on the filesystem a SUID/SGID binary that would allow other users to execute programs with the privileges of the transient user/group created by systemd. If the same UID/GID is reused by another service in the future, the SUID/SGID binary can be used to access the new service's resources.
Statement: This issue did not affect the versions of systemd as shipped with Red Hat Enterprise Linux 7 as they did not include support for DynamicUser property.
Upstream patches: https://github.com/systemd/systemd/commit/3c27973b13724ede05a06a5d346a569794cda433 https://github.com/systemd/systemd/commit/f69567cbe26d09eac9d387c0be0fc32c65a83ada https://github.com/systemd/systemd/commit/9d880b70ba5c6ca83c82952f4c90e86e56c7b70c https://github.com/systemd/systemd/commit/7445db6eb70e8d5989f481d0c5a08ace7047ae5b https://github.com/systemd/systemd/commit/62aa29247c3d74bcec0607c347f2be23cd90675d https://github.com/systemd/systemd/commit/bf65b7e0c9fc215897b676ab9a7c9d1c688143ba
References: https://bugs.chromium.org/p/project-zero/issues/detail?id=1771 https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/1814596
Created systemd tracking bugs for this issue: Affects: fedora-all [bug 1703356]
https://github.com/systemd/systemd-stable/pull/54 contains a backport for v241-stable.
Acknowledgments: Name: Jann Horn (Google Project Zero)
This issue has been addressed in the following products: Red Hat Enterprise Linux 8 Via RHSA-2020:1794 https://access.redhat.com/errata/RHSA-2020:1794
This bug is now closed. Further updates for individual products will be reflected on the CVE page(s): https://access.redhat.com/security/cve/cve-2019-3843