Vulnerability · Published Feb 10, 2021 · Assigned by canonical
CVE-2020-16120Unprivileged overlay + shiftfs read access
Medium 5.1
In plain English
A medium-severity security flaw in Linux kernel from Linux kernel. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 36% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
Overlayfs did not properly perform permission checking when copying up files in an overlayfs and could be exploited from within a user namespace, if, for example, unprivileged user namespaces were allowed. It was possible to have a file not readable by an unprivileged user to be copied to a mountpoint controlled by the user, like a removable device. This was introduced in kernel version 4.19 by commit d1d04ef ("ovl: stack file ops"). This was fixed in kernel version 5.8 by commits 56230d9 ("ovl: verify permissions in ovl_path_open()"), 48bd024 ("ovl: switch to mounter creds in readdir") and 05acefb ("ovl: check permission to open real file"). Additionally, commits 130fdbc ("ovl: pass correct flags for opening real directory") and 292f902 ("ovl: call secutiry hook in ovl_real_ioctl()") in kernel 5.8 might also be desired or necessary. These additional commits introduced a regression in overlay mounts within user namespaces which prevented access to files with ownership outside of the user namespace. This regression was mitigated by subsequent commit b6650da ("ovl: do not fail because of O_NOATIMEi") in kernel 5.11.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | linux | 5.8.7-1 | DEBIAN-CVE-2020-16120 |
| Debian:13 | linux | 5.8.7-1 | DEBIAN-CVE-2020-16120 |
| Debian:14 | linux | 5.8.7-1 | DEBIAN-CVE-2020-16120 |
| Ubuntu:22.04:LTS | linux-intel-iot-realtime | no fix listed | UBUNTU-CVE-2020-16120 |
| Ubuntu:22.04:LTS | linux-lowlatency-hwe-6.2 | no fix listed | UBUNTU-CVE-2020-16120 |
| Ubuntu:24.04:LTS | linux-raspi-realtime | no fix listed | UBUNTU-CVE-2020-16120 |
| Ubuntu:22.04:LTS | linux-realtime | no fix listed | UBUNTU-CVE-2020-16120 |
| Ubuntu:22.04:LTS | linux-riscv | no fix listed | UBUNTU-CVE-2020-16120 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Linux kernel | Linux kernel | 5.11-stable – before 5.11.0 |
Weakness: CWE-266 · Vector: CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
References
- https://ubuntu.com/USN-4576-1 vendor-advisory, x_refsource_UBUNTU
- https://ubuntu.com/USN-4577-1 vendor-advisory, x_refsource_UBUNTU
- https://ubuntu.com/USN-4578-1 vendor-advisory, x_refsource_UBUNTU
- https://www.openwall.com/lists/oss-security/2020/10/14/2 x_refsource_CONFIRM
- https://launchpad.net/bugs/1894980 vendor-advisory, x_refsource_UBUNTU
- https://launchpad.net/bugs/1900141 vendor-advisory, x_refsource_UBUNTU
- https://git.kernel.org/linus/56230d956739b9cb1cbde439d76227d77979a04d x_refsource_CONFIRM
- https://git.kernel.org/linus/48bd024b8a40d73ad6b086de2615738da0c7004f x_refsource_CONFIRM
- https://git.kernel.org/linus/05acefb4872dae89e772729efb194af754c877e8 x_refsource_CONFIRM
- https://git.kernel.org/linus/d1d04ef8572bc8c22265057bd3d5a79f223f8f52 x_refsource_CONFIRM
- https://git.kernel.org/linus/b6650dab404c701d7fe08a108b746542a934da84 x_refsource_CONFIRM