The vulnerable system is bound to the network stack and the set of possible attackers extends beyond the other options listed below, up to and including the entire Internet. Such a vulnerability is often termed “remotely exploitable” and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers). An example of a network attack is an attacker causing a denial of service by sending a specially crafted TCP packet across a wide area network (e.g., CVE-2004-0230).
Attack Complexity
Low
AC
The attacker must take no measurable action to exploit the vulnerability. The attack requires no target-specific circumvention to exploit the vulnerability. An attacker can expect repeatable success against the vulnerable system.
Privileges Required
None
PR
The attacker is unauthenticated prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.
User Interaction
None
UI
The vulnerable system can be exploited without interaction from any human user, other than the attacker. Examples include: a remote attacker is able to send packets to a target system a locally authenticated attacker executes code to elevate privileges
Scope
Unchanged
S
An exploited vulnerability can only affect resources managed by the same security authority. In the case of a vulnerability in a virtualized environment, an exploited vulnerability in one guest instance would not affect neighboring guest instances.
Confidentiality
None
C
There is no impact on the confidentiality of the system; the attacker does not gain the ability to read any data.
Integrity
High
I
There is a total compromise of system integrity. There is a complete loss of system protection, resulting in the attacker being able to modify any file on the target system.
Availability
None
A
There is no impact on the availability of the system; the attacker does not have the ability to disrupt access to or use of the system.
Below is a copy: AnyDesk 7.0.9 Arbitrary File Write / Denial Of Service
# Exploit Title: AnyDesk allow arbitrary file write by symbolic link attack lead to denial-of-service attack on local machine
# Google Dork: [if applicable]
# Date: 24/5/2022
# Exploit Author: Erwin Chan
# Vendor Homepage: https://anydesk.com/en
# Software Link: https://anydesk.com/en
# Version: 7.0.9
# Tested on: Windows 11
It was found that AnyDesk (version 7.0.9) was vulnerable to arbitrary file
write by symbolic link attack leading to denial-of-service attack on local
machine. It was noted that two functions were affected.
*Affected function A*
When there was a remote connection come in, a directory under AppData of
current user (without admin privilege) and a "ad.trace" file (i.e.,
"C:\Users\<user>\AppData\Roaming\AnyDesk") will be created by "AnyDesk.exe"
with "NT Authority\SYSTEM" privilege.
*Affected function B*
After a connection was made, local or remote user could use the chat room.
The chat log was written to folder
"C:\Users\<user>\AppData\Roaming\AnyDesk\chat\" by "AnyDesk.exe" with "NT
Authority\SYSTEM" privilege. Or the local user (without admin privilege)
could change the location of the chat log to anywhere that he/she has
"Modify" privilege.
*Vulnerability Summary*
Since the directories (i.e., "C:\Users\<user>\AppData\Roaming\AnyDesk\",
"C:\Users\<user>\AppData\Roaming\AnyDesk\chat\") were assigned with
"Modify" privilege for current user, current user could modify the entire
directory. With this setup, an unprivileged user is able to achieve
arbitrary file write by creating a symbolic link to a privileged location
(e.g., C:\Windows\System32). As a result, a malicious user could
potentially deny any service by overwriting the configuration or system
file of applications such as Anti Virus solutions. It was noted that the
file content could be manipulated in affected function B such that a low
privileged user could write an arbitrary file to an arbitrary location.
*Affected function A: Exploit steps by local user (without admin privilege)*
1. Remove the directory "C:\Users\<user>\AppData\Roaming\AnyDesk"
2. Create symbolic link of "ad.trace" file to a privileged location
(e.g., C:\Windows\System32\test.file) (PoC binary could be found here:
https://github.com/googleprojectzero/symboliclink-testing-tools/blob/main/CreateSymlink/CreateSymlink_readme.txt
)
1. Connect to local machine (target machine) from a remote machine.
After the connection was initiated, the content of "ad.trace" file would be
written to target file (e.g., C:\Windows\System32\test.file)
*Affected function B: Exploit steps by local user (without admin privilege)*
1. edit username of remote connector
1. Establish a AnyDesk connection from remote. Enter arbitrary text into
the chat box. Mark down the filename of chat log
1. Remove the directory "C:\Users\<user>\AppData\Roaming\AnyDesk\chat"
2. Create symbolic link of chat log file (e.g., 657584961.txt) to a
privileged location (e.g., C:\Windows\test.conf) (PoC binary could be found
here:
https://github.com/googleprojectzero/symboliclink-testing-tools/blob/main/CreateSymlink/CreateSymlink_readme.txt
)
1. Open the chat room and enter arbitrary content into it. After that,
the content of chat room would be written to target file (e.g.,
C:\Windows\test.conf)
Please let me know if any detail need further. Thanks
Regards,
Erwin
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