CVE-2019-15794 Reference counting error in overlayfs/shiftfs error path when used in conjuction with aufs
A reference counting error in the Linux kernel's overlayfs/shiftfs error path when used with aufs can lead to use-after-free, potentially allowing privilege escalation or denial of service.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2019-15794?
CVE-2019-15794 is a high-severity use after free vulnerability in Canonical Ubuntu Linux, published on 23 Apr 2020. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
Overlayfs in the Linux kernel and shiftfs, a non-upstream patch to the Linux kernel included in the Ubuntu 5.0 and 5.3 kernel series, both replace vma->vm_file in their mmap handlers. On error the original value is not restored, and the reference is put for the file to which vm_file points. On upstream kernels this is not an issue, as no callers dereference vm_file following after call_mmap() returns an error. However, the aufs patchs change mmap_region() to replace the fput() using a local variable with vma_fput(), which will fput() vm_file, leading to a refcount underflow.
Weakness: CWE-672
Which versions are affected by CVE-2019-15794?
It affects 2 products.
Products include Canonical Ubuntu Linux, Linux kernel.
How do I fix CVE-2019-15794?
Apply the vendor's patch.
Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.
Is CVE-2019-15794 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2019-15794 exists.
Public exploit code: 1 Exploit-DB entry.
Other vulnerabilities in Canonical Ubuntu Linux
Sources
Also known as DEBIAN-CVE-2019-15794, GHSA-33f2-r445-jvq6, ROOT-OS-DEBIAN-11-CVE-2019-15794, ROOT-OS-UBUNTU-2204-CVE-2019-15794, ROOT-OS-UBUNTU-2404-CVE-2019-15794, UBUNTU-CVE-2019-15794.