CVE-2017-18344

Impact:
Important
Public Date:
2017-12-15
CWE:
CWE-125
Bugzilla:
1610958: CVE-2017-18344 kernel: out-of-bounds access in the show_timer function in kernel/time/posix-timers.c
The timer_create syscall implementation in kernel/time/posix-timers.c in the Linux kernel doesn't properly validate the sigevent->sigev_notify field, which leads to out-of-bounds access in the show_timer function.

Find out more about CVE-2017-18344 from the MITRE CVE dictionary dictionary and NIST NVD.

CVSS v3 metrics

CVSS3 Base Score 7.1
CVSS3 Base Metrics CVSS:3.0/AV:L/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N
Attack Vector Local
Attack Complexity Low
Privileges Required None
User Interaction None
Scope Changed
Confidentiality High
Integrity Impact None
Availability Impact None

Red Hat Security Errata

Platform Errata Release Date
Red Hat MRG Grid for RHEL 6 Server v.2 (kernel-rt) RHSA-2018:3586 2018-11-13
Red Hat Enterprise Linux Extended Update Support 7.5 (kernel) RHSA-2018:3459 2018-11-06
Red Hat Enterprise Linux 7 (kernel) RHSA-2018:3083 2018-10-30
Red Hat Enterprise Linux Server TUS (v. 7.2) (kernel) RHSA-2018:3590 2018-11-13
Red Hat Enterprise Linux for Real Time for NFV (v. 7) (kernel-rt) RHSA-2018:3096 2018-10-30
Red Hat Enterprise Linux Extended Update Support 7.4 (kernel) RHSA-2018:3540 2018-11-13
Red Hat Enterprise Linux Advanced Update Support 7.2 (kernel) RHSA-2018:3590 2018-11-13
Red Hat Enterprise Linux 7 (kernel-alt) RHSA-2018:2948 2018-10-30
Red Hat Enterprise Linux Extended Update Support 7.3 (kernel) RHSA-2018:3591 2018-11-13
Red Hat Enterprise Linux Server Update Services for SAP Solutions 7.2 (kernel) RHSA-2018:3590 2018-11-13

Affected Packages State

Platform Package State
Red Hat Enterprise MRG 2 realtime-kernel Affected
Red Hat Enterprise Linux 6 kernel Not affected
Red Hat Enterprise Linux 5 kernel Not affected

Mitigation

Attached to this bugzilla is a systemtap script that will prevent opening (and therefore reading) the /proc/<process>/timers file which is used to leak information.

The SystemTap script is relatively small and efficient, broken into 3 distinct sections as follows:

--------

probe kernel.function("proc_timers_open@fs/proc/base.c").return {
        // this is -EACCES
$return = -13;
        message = sprintf("CVE-2017-18344 mitigation denied access to %s to %s(%d)", file_name , execname(), pid());
        // print a warning message at KERN_INFO debug level
        printk(6, message);
}

probe begin {
        printk(6, "Mitigation for CVE-2017-18344 loaded.\n");
}

probe end {
        printk(6, "Mitigation for CVE-2017-18344 unloaded.\n");
}

---------

First, the script places a probe at the return of the kernel function “proc_timers_open” when called. This modifies the return value to be EACCES which would return this value to userspace preventing this file from being opened. When the /proc/<pid>/timer file is attempted to be opened, a message will be logged to the kernel log subsystem showing the process and pid of the application attempting to access the timer file.

This file is not in widespread use at this time, although some applications may read from it to debug or understand their own timers that are set. This mitigation will not be useful in this context.

Finally, the “probe begin” and “probe end” code blocks tell systemtap to add the supplied text to the kernel log buffer via the printk function. This creates an audit trail by registering in the system logs exactly when the mitigation is loaded and unloaded. This will need to be compiled with guru mode (-g parameter) to compile.

This will need to be loaded at each boot to remain effective. Red Hat Product security recommends updating to a patched kernel when it is available.

Red Hat always seeks to provide both mitigations to disable attacks as well as the actual patches to treat the flaw. To learn more about SystemTap, and how it can be used in your management of your Red Hat systems, please refer to Using SystemTap[1] or one of our videos about it within our Customer Portal[2].

1 - https://access.redhat.com/articles/17839
2 - https://access.redhat.com/search/#/?q=systemtap

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