CVE-2017-1000405

Impact:
Important
Public Date:
2017-11-30
CWE:
CWE-362
Bugzilla:
1516514: CVE-2017-1000405 kernel: pmd can become dirty without going through a COW cycle
A flaw was found in the patches used to fix the 'dirtycow' vulnerability (CVE-2016-5195). An attacker, able to run local code, can exploit a race condition in transparent huge pages to modify usually read-only huge pages.

Find out more about CVE-2017-1000405 from the MITRE CVE dictionary dictionary and NIST NVD.

Statement

From the initial flaw description released, this issue does not affect the Linux kernel packages as shipped with Red Hat Enterprise Linux 5, 6, 7 and Red Hat Enterprise MRG 2. They do not contain the upstream commit (8310d48b125d19fcd9521d83b8293e63eb1646aa) which allows the race condition. This issue affects the Linux kernel packages as shipped with Red Hat Enterprise Linux 7 for ARM and Red Hat Enterprise Linux for Power LE kernel-alt packages. Future Linux kernel updates for the respective releases may address this issue. For further information please refer to the vulnerability article in the Customer Portal: https://access.redhat.com/security/vulnerabilities/3253921

CVSS v3 metrics

NOTE: The following CVSS v3 metrics and score provided are preliminary and subject to review.

CVSS3 Base Score 6.1
CVSS3 Base Metrics CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:L
Attack Vector Local
Attack Complexity Low
Privileges Required Low
User Interaction None
Scope Unchanged
Confidentiality None
Integrity Impact High
Availability Impact Low

Affected Packages State

Platform Package State
Red Hat Enterprise MRG 2 realtime-kernel Not affected
Red Hat Enterprise Linux a kernel-alt Affected
Red Hat Enterprise Linux 7 kernel Not affected
Red Hat Enterprise Linux 7 kernel-rt Not affected
Red Hat Enterprise Linux 6 kernel Not affected
Red Hat Enterprise Linux 5 kernel Not affected

Acknowledgements

Red Hat would like to thank Eylon Ben Yaakov and Daniel Shapiro for reporting this issue.

Mitigation

Disabling the use of zero page: It is possible to prevent the zero page from being mapped as a huge page, by modifying a configuration tunable in the /sys directory as shown below. This prevents the flaw from being exercised in this method. # echo 0 > /sys/kernel/mm/transparent_hugepage/use_zero_page Disabling huge pages: It is possible to mitigate this flaw by disabling hugepages on a system. Some user applications may require hugepages to be performant, and may suffer a performance penalty when running without hugepages. Red Hat has existing solutions created instructing how to disable transparent How to disable transparent hugepages (THP) on Red Hat Enterprise Linux 7 https://access.redhat.com/solutions/1320153 If your application may require transparent huge pages, please consult your software vendor to confirm.

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