CVE-2017-1000405
Nevertheless, it does allow us to overwrite read-only huge pages.
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (2.84%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.
Description
The Linux Kernel versions 2.6.38 through 4.14 have a problematic use of pmd_mkdirty() in the touch_pmd() function inside the THP implementation. touch_pmd() can be reached by get_user_pages(). In such case, the pmd will become dirty. This scenario breaks the new can_follow_write_pmd()'s logic - pmd can become dirty without going through a COW cycle. This bug is not as severe as the original "Dirty cow" because an ext4 file (or any other regular file) cannot be mapped using THP. Nevertheless, it does allow us to overwrite read-only huge pages. For example, the zero huge page and sealed shmem files can be overwritten (since their mapping can be populated using THP). Note that after the first write page-fault to the zero page, it will be replaced with a new fresh (and zeroed) thp.
- CVSS 3.1
- 7.0 HIGHCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
- EPSS
- 2.84% probability · 86th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-362
- Affected
- linux/linux kernel
- Source
- cve@mitre.org
References
- http://www.securityfocus.com/bid/102032Third Party Advisory, VDB Entry
- http://www.securitytracker.com/id/1040020Third Party Advisory, VDB Entry
- https://access.redhat.com/errata/RHSA-2018:0180Third Party Advisory
- https://medium.com/bindecy/huge-dirty-cow-cve-2017-1000405-110eca132de0Exploit, Issue Tracking, Third Party Advisory
- https://source.android.com/security/bulletin/pixel/2018-02-01Third Party Advisory
- https://www.exploit-db.com/exploits/43199/Exploit, Issue Tracking, Third Party Advisory, VDB Entry
- http://www.securityfocus.com/bid/102032Third Party Advisory, VDB Entry
- http://www.securitytracker.com/id/1040020Third Party Advisory, VDB Entry
- https://access.redhat.com/errata/RHSA-2018:0180Third Party Advisory
- https://medium.com/bindecy/huge-dirty-cow-cve-2017-1000405-110eca132de0Exploit, Issue Tracking, Third Party Advisory
- https://source.android.com/security/bulletin/pixel/2018-02-01Third Party Advisory
- https://www.exploit-db.com/exploits/43199/Exploit, Issue Tracking, Third Party Advisory, VDB Entry
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.