The userfaultfd implementation in the Linux kernel before 4.19.7 mishandles access control for certain UFFDIO_ ioctl calls, as demonstrated by allowing local users to write data into holes in a tmpfs file (if the user has read-only access to that file, and that file contains holes), related to fs/userfaultfd.c and mm/userfaultfd.c.
https://access.redhat.com/errata/RHBA-2019:0327
https://access.redhat.com/errata/RHSA-2019:0163
https://access.redhat.com/errata/RHSA-2019:0202
https://access.redhat.com/errata/RHSA-2019:0324
https://access.redhat.com/errata/RHSA-2019:0831
https://bugs.chromium.org/p/project-zero/issues/detail?id=1700
https://cdn.kernel.org/pub/linux/kernel/v4.x/ChangeLog-4.14.87
https://cdn.kernel.org/pub/linux/kernel/v4.x/ChangeLog-4.19.7
https://github.com/torvalds/linux/commit/29ec90660d68bbdd69507c1c8b4e33aa299278b1
https://usn.ubuntu.com/3901-1/
https://usn.ubuntu.com/3901-2/
Source: MITRE
Published: 2018-12-12
Updated: 2020-08-24
Type: CWE-863
Base Score: 2.1
Vector: AV:L/AC:L/Au:N/C:N/I:P/A:N
Impact Score: 2.9
Exploitability Score: 3.9
Severity: LOW
Base Score: 5.5
Vector: CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N
Impact Score: 3.6
Exploitability Score: 1.8
Severity: MEDIUM