Ubuntu overlayfs privilege elevation

2015-06-2600:00:00

SAINT Corporation

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7.8 High

CVSS3

Attack Vector

LOCAL

Attack Complexity

LOW

Privileges Required

LOW

User Interaction

NONE

Scope

UNCHANGED

Confidentiality Impact

HIGH

Integrity Impact

HIGH

Availability Impact

HIGH

CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

7.2 High

CVSS2

Access Vector

LOCAL

Access Complexity

LOW

Authentication

NONE

Confidentiality Impact

COMPLETE

Integrity Impact

COMPLETE

Availability Impact

COMPLETE

AV:L/AC:L/Au:N/C:C/I:C/A:C

0.001 Low

EPSS

Percentile

24.9%

JSON

Added: 06/26/2015
CVE: CVE-2015-1328
BID: 75206

Background

Overlayfs is a type of file system for Linux which implements a union mount.

Problem

In Ubuntu, overlayfs fails to correctly check file permissions when creating new files in the upper filesystem directory. This can be exploited by an unprivileged user to write arbitrary files, leading to command execution with root privileges.

Resolution

Apply one of the fixes from Ubuntu.

References

<http://seclists.org/oss-sec/2015/q2/717>

Limitations

Exploit works in Ubuntu 12.04, 14.04, 14.10, and 15.04. The kernel must have **CONFIG_USER_NS=y** and overlayfs must have the **FS_USERNS_MOUNT** flag in order for the exploit to succeed. gcc must be installed on the target.