CVE-2017-2636

Impact:
Important
Public Date:
2017-03-07
CWE:
CWE-362
Bugzilla:
1428319: CVE-2017-2636 kernel: Race condition access to n_hdlc.tbuf causes double free in n_hdlc_release()
A race condition flaw was found in the N_HLDC Linux kernel driver when accessing n_hdlc.tbuf list that can lead to double free. A local, unprivileged user able to set the HDLC line discipline on the tty device could use this flaw to increase their privileges on the system.

Find out more about CVE-2017-2636 from the MITRE CVE dictionary dictionary and NIST NVD.

Statement

This issue does not affect the Linux kernel packages as shipped with Red Hat Enterprise Linux 5.

This issue does affect the Linux kernel packages as shipped with Red Hat Enterprise Linux 6, 7 and Red Hat Enterprise MRG 2. As this issue is rated as Important, it has been scheduled to be fixed in future updates for the respective releases.

CVSS v3 metrics

CVSS3 Base Score 7.8
CVSS3 Base Metrics CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Attack Vector Local
Attack Complexity Low
Privileges Required Low
User Interaction None
Scope Unchanged
Confidentiality High
Integrity Impact High
Availability Impact High

Red Hat Security Errata

Platform Errata Release Date
Red Hat Enterprise Linux 6 (kernel) RHSA-2017:0892 2017-04-11
Red Hat Enterprise Linux Server TUS (v. 6.6) (kernel) RHSA-2017:1488 2017-06-19
Red Hat Enterprise Linux 7 (kernel) RHSA-2017:0933 2017-04-12
Red Hat Enterprise Linux Server TUS (v. 6.5) (kernel) RHSA-2017:1232 2017-05-16
Red Hat Enterprise Linux for Real Time for NFV (v. 7) (kernel-rt) RHSA-2017:0931 2017-04-12
Red Hat Enterprise Linux Advanced Update Support 6.5 (kernel) RHSA-2017:1232 2017-05-16
Red Hat MRG Grid for RHEL 6 Server v.2 (kernel-rt) RHSA-2017:0932 2017-04-12
Red Hat Enterprise Linux Advanced Update Support 6.4 (kernel) RHSA-2017:0986 2017-04-18
Red Hat Enterprise Linux Extended Update Support 6.7 (kernel) RHSA-2017:1233 2017-05-16
Red Hat Enterprise Linux Extended Update Support 7.2 (kernel) RHSA-2017:1125 2017-04-25
Red Hat Enterprise Linux Advanced Update Support 6.2 (kernel) RHSA-2017:1126 2017-04-25
Red Hat Enterprise Linux Advanced Update Support 6.6 (kernel) RHSA-2017:1488 2017-06-19

Affected Packages State

Platform Package State
Red Hat Enterprise Linux 5 kernel Not affected

Acknowledgements

Red Hat would like to thank Alexander Popov for reporting this issue.

Mitigation

The n_hdlc kernel module will be automatically loaded when an application attempts to use the HDLC line discipline from userspace. This module can be prevented from being loaded by using the system-wide modprobe rules. The following command, run as root, will prevent accidental or intentional loading of the module. Red Hat Product Security believe this method is a robust method to prevent accidental loading of the module, even by privileged users.

​# echo "install n_hdlc /bin/true" >> /etc/modprobe.d/disable-n_hdlc.conf

The system will need to be restarted if the n_hdlc modules are already loaded. In most circumstances, the n_hdlc kernel modules will be unable to be unloaded if in use and while any current process using this line discipline is required.

Exploiting this flaw does not require Microgate or SyncLink hardware to be in use.

If further assistance is needed, see this KCS article ( https://access.redhat.com/solutions/41278 ) or contact Red Hat Global Support Services.

External References

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