CVE-2024-4418: Race Condition in libvirt Leading to Stack Use-After-Free Flaw

A race condition is a situation in which the behavior of a system depends on the relative timing of events. When two or more threads access shared data concurrently, the final value of the shared data depends on which thread runs last. This can lead to unpredictable results and security vulnerabilities.

A stack use-after-free flaw has been found in libvirt, a popular open-source virtualization API used for managing virtual machines and other virtualization functionality. The flaw occurs due to a race condition created by a bad assumption made in the virNetClientIOEventLoop() method. This vulnerability allows a local, unprivileged user to access the virtproxyd daemon without authentication, potentially leading to a user escaping from their otherwise limited access.

Details of the Vulnerability (CVE-2024-4418)

Libvirt incorrectly assumes that the data pointer to a stack-allocated virNetClientIOEventData structure will not be used in the virNetClientIOEventFD callback while the data pointer's stack frame is concurrently being "freed" when returning from virNetClientIOEventLoop(). This mistake results in a race condition and a stack use-after-free flaw.

The following code snippet shows the issue

static int
virNetClientIOEventLoop(virNetClientPtr client,
                         virNetClientIncomingPtr incoming)
{
    ...
    virNetClientIOEventData data;

    ...
    for (;;) {
        ...
        rc = virEventRunDefaultImpl();
        if (rc < ) {
            ...
            goto cleanup;
        }
    }

cleanup:
    ...
    virObjectUnlock(client);
    return ret;
}

The problem arises when the virNetClientIOEventFD callback is executed, which uses the data pointer after the stack frame has been freed:

static void
virNetClientIOEventFD(int watch ATTRIBUTE_UNUSED, int fd ATTRIBUTE_UNUSED,
                      int events, void *opaque)
{
    virNetClientIOEventDataPtr data = opaque;
    ...
}

Exploiting this vulnerability is made possible through the virtproxyd daemon, which can be used to trigger requests. If libvirt is configured with fine-grained access control, this could allow a user to bypass their limitations and access information or resources they should not have access to.

Impact

This flaw impacts systems using libvirt with virtproxyd daemon and fine-grained access control. Local, unprivileged users can potentially exploit this vulnerability to access virtproxyd without authentication. Remote users would need to authenticate before they could access it.

Mitigation

To protect against this vulnerability, users are advised to update their libvirt installations to the latest version, which contains a patch that fixes this issue. Users can also restrict access to the virtproxyd daemon or disable it altogether if it is not required.

Original References

1. CVE-2024-4418 - Red Hat Customer Portal
2. libvirt Security Vulnerability
3. Race condition leading to stack use-after-free in libvirt

In conclusion, the race condition and stack use-after-free vulnerability (CVE-2024-4418) in libvirt pose a security risk to systems that employ libvirt with the virtproxyd daemon and fine-grained access control. Users are urged to update their installations and take necessary precautions to minimize the risk of exploitation.

Timeline

Published on: 05/08/2024 03:15:07 UTC
Last modified on: 08/02/2024 19:18:05 UTC