CVE-2020-27786
📋 TL;DR
This CVE describes a use-after-free vulnerability in the Linux kernel's MIDI subsystem. An attacker with local access and permissions to issue ioctl commands to MIDI devices could trigger memory corruption, potentially leading to privilege escalation or system crashes. This affects Linux systems with vulnerable kernel versions where local users have access to MIDI devices.
💻 Affected Systems
- Linux kernel
📦 What is this software?
Linux Kernel by Linux
The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...
Learn more about Linux Kernel →Linux Kernel by Linux
The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...
Learn more about Linux Kernel →Linux Kernel by Linux
The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...
Learn more about Linux Kernel →Linux Kernel by Linux
The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...
Learn more about Linux Kernel →Linux Kernel by Linux
The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...
Learn more about Linux Kernel →Linux Kernel by Linux
The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...
Learn more about Linux Kernel →⚠️ Risk & Real-World Impact
Worst Case
Full privilege escalation to root, allowing complete system compromise including data theft, persistence installation, and denial of service.
Likely Case
Local privilege escalation allowing attackers to gain root access on affected systems, potentially leading to lateral movement within networks.
If Mitigated
Limited impact with proper access controls preventing unauthorized users from accessing MIDI devices and timely patching.
🎯 Exploit Status
Exploit requires local access and specific permissions. Public exploit code exists in security advisories and mailing lists.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Linux kernel with commit c1f6e3c818dd734c30f6a7eeebf232ba2cf3181d or later
Vendor Advisory: https://bugzilla.redhat.com/show_bug.cgi?id=1900933
Restart Required: Yes
Instructions:
1. Update Linux kernel to version containing fix commit c1f6e3c818dd. 2. Check distribution-specific security updates. 3. Reboot system to load new kernel.
🔧 Temporary Workarounds
Restrict MIDI device access
linuxRemove or restrict permissions to MIDI devices to prevent unauthorized users from accessing them.
chmod 600 /dev/snd/*
chown root:root /dev/snd/*
Disable MIDI module
linuxBlacklist or disable the MIDI kernel module if not needed.
echo 'blacklist snd-seq-midi' >> /etc/modprobe.d/blacklist.conf
rmmod snd-seq-midi
🧯 If You Can't Patch
- Implement strict access controls on MIDI devices using file permissions and user groups.
- Monitor for suspicious activity related to MIDI device access and privilege escalation attempts.
🔍 How to Verify
Check if Vulnerable:
Check kernel version and if commit c1f6e3c818dd is present: uname -r && git log --oneline | grep c1f6e3c818ddCheck Version:
uname -rVerify Fix Applied:
Verify kernel version is updated and commit c1f6e3c818dd appears in kernel changelog.📡 Detection & Monitoring
Log Indicators:
- Failed or successful privilege escalation attempts
- Unusual access to /dev/snd/* devices
- Kernel panic or crash logs
Network Indicators:
- None - local exploit only
SIEM Query:
source="kernel" AND ("privilege escalation" OR "use-after-free" OR "/dev/snd/")🔗 References
- http://www.openwall.com/lists/oss-security/2020/12/03/1
- https://bugzilla.redhat.com/show_bug.cgi?id=1900933
- https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=c1f6e3c818dd734c30f6a7eeebf232ba2cf3181d
- https://security.netapp.com/advisory/ntap-20210122-0002/
- http://www.openwall.com/lists/oss-security/2020/12/03/1
- https://bugzilla.redhat.com/show_bug.cgi?id=1900933
- https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=c1f6e3c818dd734c30f6a7eeebf232ba2cf3181d
- https://security.netapp.com/advisory/ntap-20210122-0002/
