CVE-2019-15791 Reference count underflow in shiftfs

What is CVE-2019-15791?

CVE-2019-15791 is a high-severity 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

In shiftfs, a non-upstream patch to the Linux kernel included in the Ubuntu 5.0 and 5.3 kernel series, shiftfs_btrfs_ioctl_fd_replace() installs an fd referencing a file from the lower filesystem without taking an additional reference to that file. After the btrfs ioctl completes this fd is closed, which then puts a reference to that file, leading to a refcount underflow.

Weakness: CWE-191, CWE-672

Which versions are affected by CVE-2019-15791?

It affects 2 products.

Products include Canonical Ubuntu Linux, Linux kernel.

How do I fix CVE-2019-15791?

Apply the vendor's patch.

Is CVE-2019-15791 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2019-15791 exists.

Public exploit code: 1 Exploit-DB entry.

Other vulnerabilities in Canonical Ubuntu Linux

• CVE-2020-11651 SaltStack Salt Authentication Bypass Exploited Critical 9.8
• CVE-2020-7247 OpenSMTPD Remote Code Execution Exploited Critical 9.8
• CVE-2019-16928 Exim Out-of-bounds Write Exploited Critical 9.8
• CVE-2018-6789 Exim Buffer Overflow Exploited Critical 9.8
• CVE-2015-2590 Oracle Java SE and Java SE Embedded Remote Code Execution Exploited Critical 9.8

All Canonical Ubuntu Linux vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as GHSA-5fx5-7qgj-cmg7, UBUNTU-CVE-2019-15791.