Vulnerability 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.
CVSS Score
MEDIUM
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Linux | Linux Kernel | < 5.11 |
| Canonical | Ubuntu Linux | 14.04 |
Related Weaknesses (CWE)
References
- https://git.kernel.org/linus/05acefb4872dae89e772729efb194af754c877e8PatchThird Party Advisory
- https://git.kernel.org/linus/48bd024b8a40d73ad6b086de2615738da0c7004fPatchThird Party Advisory
- https://git.kernel.org/linus/56230d956739b9cb1cbde439d76227d77979a04dPatchThird Party Advisory
- https://git.kernel.org/linus/b6650dab404c701d7fe08a108b746542a934da84PatchThird Party Advisory
- https://git.kernel.org/linus/d1d04ef8572bc8c22265057bd3d5a79f223f8f52PatchThird Party Advisory
- https://launchpad.net/bugs/1894980Issue TrackingPatchThird Party Advisory
- https://launchpad.net/bugs/1900141Issue TrackingThird Party Advisory
- https://ubuntu.com/USN-4576-1Third Party Advisory
- https://ubuntu.com/USN-4577-1Third Party Advisory
- https://ubuntu.com/USN-4578-1Third Party Advisory
- https://www.openwall.com/lists/oss-security/2020/10/14/2Mailing ListThird Party Advisory
- https://git.kernel.org/linus/05acefb4872dae89e772729efb194af754c877e8PatchThird Party Advisory
- https://git.kernel.org/linus/48bd024b8a40d73ad6b086de2615738da0c7004fPatchThird Party Advisory
- https://git.kernel.org/linus/56230d956739b9cb1cbde439d76227d77979a04dPatchThird Party Advisory
- https://git.kernel.org/linus/b6650dab404c701d7fe08a108b746542a934da84PatchThird Party Advisory
FAQ
What is CVE-2020-16120?
CVE-2020-16120 is a vulnerability with a CVSS score of 5.1 (MEDIUM). 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 all...
How severe is CVE-2020-16120?
CVE-2020-16120 has been rated MEDIUM with a CVSS base score of 5.1/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2020-16120?
Check the references section above for vendor advisories and patch information. Affected products include: Linux Linux Kernel, Canonical Ubuntu Linux.