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CVE-2020-16120 Detail

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.


Metrics

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CVSS 4.0 Severity and Vector Strings:

NIST CVSS score
NIST: NVD
N/A
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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
NVD-CWE-Other Other cwe source acceptance level NIST  
CWE-266 Incorrect Privilege Assignment Canonical Ltd.  

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Change History

3 change records found show changes

Quick Info

CVE Dictionary Entry:
CVE-2020-16120
NVD Published Date:
02/10/2021
NVD Last Modified:
11/18/2021
Source:
Canonical Ltd.