CVE-2020-1712
📋 TL;DR
A heap use-after-free vulnerability in systemd before version v245-rc1 allows local unprivileged attackers to crash systemd services or potentially execute arbitrary code and elevate privileges by sending specially crafted dbus messages. This affects Linux systems using vulnerable systemd versions for asynchronous Polkit queries during dbus message handling.
💻 Affected Systems
- systemd
📦 What is this software?
Discovery by Redhat
Systemd by Systemd Project
⚠️ Risk & Real-World Impact
Worst Case
Local privilege escalation to root, allowing complete system compromise and persistence.
Likely Case
Service disruption through denial of service (systemd service crashes) with potential for privilege escalation in targeted attacks.
If Mitigated
Limited to service disruption if proper access controls prevent local user access or if exploit attempts are detected and blocked.
🎯 Exploit Status
Exploit requires local access and crafting specific dbus messages. Proof-of-concept code has been published in security advisories.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: v245-rc1 and later
Vendor Advisory: https://bugzilla.redhat.com/show_bug.cgi?id=CVE-2020-1712
Restart Required: Yes
Instructions:
1. Update systemd package using distribution's package manager. 2. For RHEL/CentOS: 'yum update systemd'. 3. For Ubuntu/Debian: 'apt update && apt upgrade systemd'. 4. Reboot system to ensure all services use patched version.
🔧 Temporary Workarounds
Restrict dbus access
linuxLimit dbus message handling through Polkit policies to reduce attack surface
Configure Polkit policies to restrict dbus message processing for sensitive operations
Disable unnecessary systemd services
linuxReduce exposure by disabling non-essential systemd services that use dbus messaging
systemctl disable [service-name]
systemctl mask [service-name]
🧯 If You Can't Patch
- Implement strict access controls to prevent local user access to vulnerable systems
- Monitor for suspicious dbus message patterns and systemd service crashes
🔍 How to Verify
Check if Vulnerable:
Check systemd version: 'systemd --version' or 'rpm -q systemd' or 'dpkg -l systemd' and compare to v245-rc1Check Version:
systemd --version | head -1Verify Fix Applied:
Verify systemd version is v245-rc1 or later and check for applied patches in package manager history📡 Detection & Monitoring
Log Indicators:
- Systemd service crashes in journalctl logs
- Unusual dbus message patterns
- Polkit authentication failures
Network Indicators:
- Local dbus message spikes (monitor via dbus-monitor)
SIEM Query:
source="journald" AND (process="systemd" OR process="dbus") AND (message="segmentation fault" OR message="use-after-free" OR message="crash")🔗 References
- https://bugzilla.redhat.com/show_bug.cgi?id=CVE-2020-1712
- https://github.com/systemd/systemd/commit/1068447e6954dc6ce52f099ed174c442cb89ed54
- https://github.com/systemd/systemd/commit/637486261528e8aa3da9f26a4487dc254f4b7abb
- https://github.com/systemd/systemd/commit/bc130b6858327b382b07b3985cf48e2aa9016b2d
- https://github.com/systemd/systemd/commit/ea0d0ede03c6f18dbc5036c5e9cccf97e415ccc2
- https://lists.debian.org/debian-lts-announce/2022/06/msg00025.html
- https://www.openwall.com/lists/oss-security/2020/02/05/1
- https://bugzilla.redhat.com/show_bug.cgi?id=CVE-2020-1712
- https://github.com/systemd/systemd/commit/1068447e6954dc6ce52f099ed174c442cb89ed54
- https://github.com/systemd/systemd/commit/637486261528e8aa3da9f26a4487dc254f4b7abb
- https://github.com/systemd/systemd/commit/bc130b6858327b382b07b3985cf48e2aa9016b2d
- https://github.com/systemd/systemd/commit/ea0d0ede03c6f18dbc5036c5e9cccf97e415ccc2
- https://lists.debian.org/debian-lts-announce/2022/06/msg00025.html
- https://www.openwall.com/lists/oss-security/2020/02/05/1
