7.8 High
CVSS3
Attack Vector
LOCAL
Attack Complexity
LOW
Privileges Required
LOW
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
HIGH
Integrity Impact
HIGH
Availability Impact
HIGH
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
7.2 High
CVSS2
Access Vector
LOCAL
Access Complexity
LOW
Authentication
NONE
Confidentiality Impact
COMPLETE
Integrity Impact
COMPLETE
Availability Impact
COMPLETE
AV:L/AC:L/Au:N/C:C/I:C/A:C
0.003 Low
EPSS
Percentile
63.8%
Windows User Profile Service Elevation of Privilege Vulnerability. This CVE ID is unique from CVE-2022-21895.
Recent assessments:
gwillcox-r7 at January 12, 2022 12:07am UTC reported:
Update: As predicted there is a patch bypass for this, now labled as CVE-2022-26904
According to <https://twitter.com/KLINIX5/status/1480996599165763587> this appears to be a patch for the code blogged about at <https://halove23.blogspot.com/2021/10/windows-user-profile-service-0day.html>. The details on this bug can be found at <https://github.com/klinix5/ProfSvcLPE/blob/main/write-up.docx> but I’ll summarize them here for brevity.
The original incomplete patch, aka CVE-2021-34484 is explained best by Mitja Kolsek at <https://blog.0patch.com/2021/11/micropatching-incompletely-patched.html> where he notes that bug was originally considered to be an arbitrary directory deletion bug that allowed a logged on user to delete a folder on the computer.
However upon reviewing the fix KLINUX5 found that it was possible to not only bypass the fix, but also make the vulnerability more impactful.
Specifically by abusing the User Profile Service’s code which creates a temporary user profile folder (to protect against the original user profile folder being damaged etc), and then copies folders and files from the original profile folder to the backup, one can instead place a symbolic link. When this symbolic link is followed, it can allow the attacker to create attacker-writeable folders in a protected location and then perform a DLL hijacking attack against high privileged system processes.
Unfortunately when patching this bug, Microsoft correctly assumed that one should check that the temporary user folder (aka C:\Users\TEMP
), is not a symbolic link, but didn’t check to see if any of the folders under C:\Users\TEMP
contains a symbolic link.
Note that as noted in <https://blog.0patch.com/2021/11/micropatching-incompletely-patched.html> this bug does require winning a race condition so exploitation is 100% reliable however there are ways to win the race condition as was shown in the code for the patch bypass published at <https://github.com/klinix5/ProfSvcLPE/tree/main/DoubleJunctionEoP>.
I’d keep an eye on this one as KLINIX5 has a habit of finding patch bypasses for his bugs and if he says Microsoft has messed things up again, more than likely there will be another patch bypass for this bug. I’m still looking into exactly what was patched here though.
Assessed Attacker Value: 4
Assessed Attacker Value: 4Assessed Attacker Value: 3
7.8 High
CVSS3
Attack Vector
LOCAL
Attack Complexity
LOW
Privileges Required
LOW
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
HIGH
Integrity Impact
HIGH
Availability Impact
HIGH
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
7.2 High
CVSS2
Access Vector
LOCAL
Access Complexity
LOW
Authentication
NONE
Confidentiality Impact
COMPLETE
Integrity Impact
COMPLETE
Availability Impact
COMPLETE
AV:L/AC:L/Au:N/C:C/I:C/A:C
0.003 Low
EPSS
Percentile
63.8%