Eryk Sun <eryk...@gmail.com> added the comment:
> There is no reason why a user should be able to write to
> HKCU but not HKLM.
Modifying system keys is limited to SYSTEM, administrators, and various
privileged accounts and services such as TrustedInstaller. Standard users are
not allowed to modify system keys.
> User is a local admin on the machine, and UAC is disabled as well.
Please show the output from running the following:
import subprocess
import winreg
print(subprocess.check_output('whoami.exe /groups /fo list', text=True))
hkey = winreg.HKEY_LOCAL_MACHINE
winreg.OpenKey(hkey, 'SOFTWARE', 0, winreg.KEY_ALL_ACCESS)
If it shows that the administrators group is enabled but full access is still
denied to the system "SOFTWARE" hive, then something peculiar is happening here
that warrants further inspection.
---
Background
The base object type that implements the registry is the Key type. A key object
can contain other keys and values, or a symbolic link to another key. A key can
also be mounted by a hive, which is a tree of keys that's persisted in a file.
The root key is named "\REGISTRY". The system mounts user profile hives (i.e.
"<userprofile>\NTUSER.DAT") on subkeys of "\REGISTRY\USER" and system hives on
subkeys of "\REGISTRY\MACHINE". Each loaded user profile hive is mounted on a
subkey that's named for the user's SID string -- e.g.
"\REGISTRY\USER\S-1-5-21-<domain id>-<relative id>", except the default user
profile hive is mounted as "\REGISTRY\USER\.DEFAULT". The mounted system hives
include BCD00000000 (boot configuration database), SYSTEM, SOFTWARE, SECURITY,
and SAM. The system hives, with the exception of the BCD hive, are found on
disk in the directory "%SystemRoot%\System32\config".
The "\REGISTRY\USER" and "\REGISTRY\MACHINE" keys are made available via the
predefined handles HKEY_USERS and HKEY_LOCAL_MACHINE. These predefined handles
can also reference the "USER" and "MACHINE" keys on a remote system via
winreg.ConnectRegistry(). In the local case, the API maps the predefined handle
to an actual handle that it opens via NtOpenKeyEx(). In the remote case, the
predefined handle is mapped to an RPC (remote procedure call) handle that
proxies a handle on the remote system.
HKEY_CURRENT_USER is a predefined handle for the user profile key of the
current user. It exists for convenience. Otherwise a program would have to get
the name of the subkey to use by getting the current user's SID as a string.
The predefined handles that are documented to work with ConnectRegistry() are
HKEY_USERS, HKEY_LOCAL_MACHINE, and HKEY_PERFORMANCE_DATA (a virtual key that
the API implements) [1]. ConnectRegistry() is not documented to support
HKEY_CURRENT_USER. For a remote system, it opens the default profile. This is
undefined behavior for an unsupported parameter. It happens to work in the
local case when computer_name is None.
A key object is secured by a security descriptor that grants or denies specific
users and groups various standard rights and specific key rights. winreg
provides the API constants for specific key rights, as well as constants with
mapped rights for generic access, including KEY_READ, KEY_WRITE, KEY_EXECUTE,
and KEY_ALL_ACCESS. These are defined as follows:
STANDARD_RIGHTS_REQUIRED:
WRITE_OWNER
WRITE_DAC
READ_CONTROL
DELETE
KEY_READ / KEY_EXECUTE:
KEY_QUERY_VALUE
KEY_ENUMERATE_SUB_KEYS
KEY_NOTIFY
READ_CONTROL
KEY_WRITE:
KEY_SET_VALUE
KEY_CREATE_SUB_KEY
READ_CONTROL
KEY_ALL_ACCESS:
KEY_READ
KEY_WRITE
KEY_CREATE_LINK
STANDARD_RIGHTS_REQUIRED
>From the command line, you can use Sysinternals "accesschk.exe" to check the
>access that a key grants to a particular user or group, such as the "Users"
>group. For example:
C:\>accesschk -nobanner -kdv Users "HKLM\SOFTWARE\Microsoft\Windows
NT\CurrentVersion\Winlogon"
R HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
KEY_QUERY_VALUE
KEY_ENUMERATE_SUB_KEYS
KEY_NOTIFY
READ_CONTROL
Standard users are only granted read access to the "Winlogon" key. Full access
is granted to administrators, SYSTEM, and the TrustedInstaller service.
By default, if UAC is enabled, an administrator uses a non-elevated logon that
has the administrators group disabled for everything except denying access to
objects. Spawning a process with "run as administrator" uses an elevated logon
that enables the administrators group for granting access to secured objects.
---
[1]
https://docs.microsoft.com/en-us/windows/win32/api/winreg/nf-winreg-regconnectregistryw
----------
nosy: +eryksun
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