CVE-2020-16120 Detail

Current 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.


View Analysis Description

Severity



CVSS 3.x Severity and Metrics:

NIST CVSS score
NIST: NVD
Base Score:  4.4 MEDIUM
Vector:  CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:N/A:N

Nist CVSS score does not match with CNA score
CNA:  Canonical Ltd.
Base Score:  5.1 MEDIUM
Vector:  CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N


NVD Analysts use publicly available information to associate vector strings and CVSS scores. We also display any CVSS information provided within the CVE List from the CNA.

Note: It is possible that the NVD CVSS may not match that of the CNA. The most common reason for this is that publicly available information does not provide sufficient detail or that information simply was not available at the time the CVSS vector string was assigned.

References to Advisories, Solutions, and Tools

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Hyperlink Resource
https://git.kernel.org/linus/05acefb4872dae89e772729efb194af754c877e8 Patch  Third Party Advisory 
https://git.kernel.org/linus/48bd024b8a40d73ad6b086de2615738da0c7004f Patch  Third Party Advisory 
https://git.kernel.org/linus/56230d956739b9cb1cbde439d76227d77979a04d Patch  Third Party Advisory 
https://git.kernel.org/linus/b6650dab404c701d7fe08a108b746542a934da84 Patch  Third Party Advisory 
https://git.kernel.org/linus/d1d04ef8572bc8c22265057bd3d5a79f223f8f52 Patch  Third Party Advisory 
https://launchpad.net/bugs/1894980 Issue Tracking  Patch  Third Party Advisory 
https://launchpad.net/bugs/1900141 Issue Tracking  Third Party Advisory 
https://ubuntu.com/USN-4576-1 Third Party Advisory 
https://ubuntu.com/USN-4577-1 Third Party Advisory 
https://ubuntu.com/USN-4578-1 Third Party Advisory 
https://www.openwall.com/lists/oss-security/2020/10/14/2 Mailing List  Third Party Advisory 

Weakness Enumeration

CWE-ID CWE Name Source
CWE-269 Improper Privilege Management cwe source acceptance level NIST  
CWE-266 Incorrect Privilege Assignment Contributor acceptance level Canonical Ltd.  

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Change History

1 change records found show changes

Quick Info

CVE Dictionary Entry:
CVE-2020-16120
NVD Published Date:
02/10/2021
NVD Last Modified:
02/18/2021
Source:
Canonical Ltd.