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Date: Tue, 10 Dec 2019 11:30:58 +1100
From: <sandreim@...zon.com>
To: <oss-security@...ts.openwall.com>
CC: "Anthony Liguori (aliguori)" <aliguori@...zon.com>
Subject: CVE-2019-18960: Firecracker v0.18.0 and v0.19.0 vsock buffer overflow

We have identified an issue in the Firecracker v0.18.0 and v0.19.0 vsock
implementation.

# Issue Description

A logical error in bounds checking performed on vsock virtio descriptors
can be used by a malicious guest to read from and write to a segment of
the host-side Firecracker process' heap address space, directly after
the end of a guest memory region. For reads, the accessible segment's
size is 64 KiB. For writes, the accessible segment is limited by the
host Linux kernel to a size defined in /proc/sys/net/core/rmem_max. We
expect the value of rmem_max to be on the order of a few hundred KiB to
a few MiB.

# Impact

This will generally result in a segmentation fault, but remote code
execution within the Firecracker host-side process context cannot be
ruled out.

# Vulnerable Systems

Only Firecracker v0.18.0 and v0.19.0 are affected. Only Firecracker
microVMs with configured vsock devices are affected, and only if one or
more vsock devices are in active use by both host and guest.

# Mitigation

Patched binaries for the affected versions have been released as
Firecracker v0.18.1 [1] and Firecracker v0.19.1 [2].
If you are using Firecracker v0.18.0 or v0.19.0 , we recommend you apply
the provided fix. If you are using Firecracker v0.17.0 or below, you do
not need to take any action.
In a remote code execution scenario, users running Firecracker in line
with the recommended Production Host Setup will see the impact limited
as follows: a malicious microVM guest that would manage to compromise
the Firecracker VMM process would be restricted to running on the host
as an unprivileged user, in a chroot and mount namespace isolated from
the host's filesystem, in a separate pid namespace, in a separate
network namespace, with system calls limited to Firecracker's seccomp
whitelist, on a single NUMA node, and on a cgroups-limited number of CPU
cores.

[1] https://github.com/firecracker-microvm/firecracker/releases/tag/v0.18.1
[2] https://github.com/firecracker-microvm/firecracker/releases/tag/v0.19.1

Best Regards,
Andrei on behalf of the Firecracker maintainers team.




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