What’s Vulnerable › Vulnerabilities

CVE-2019-15791: Reference count underflow in shiftfs

• Severity: high (CVSS 7.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.3% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2020-04-24 · updated 2026-06-17
• Weakness: CWE-672

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.

Affected products

• Canonical Ubuntu Linux: 18.04, 19.04
• Linux kernel: 5.0, 5.3

References

• https://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/eoan/commit/?id=601a64857b3d7040ca15c39c929e6b9db3373ec1
• https://usn.ubuntu.com/usn/usn-4183-1
• https://usn.ubuntu.com/usn/usn-4184-1
• https://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/eoan/commit/?id=601a64857b3d7040ca15c39c929e6b9db3373ec1
• https://usn.ubuntu.com/usn/usn-4183-1
• https://usn.ubuntu.com/usn/usn-4184-1

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