Moderate
Nuuo Central Management Server Session Bruteforce
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Nuuo Central Management Server Session Bruteforce
MITRE ATT&CK
Collection
Command and Control
Credential Access
Defense Evasion
Discovery
Execution
Exfiltration
Impact
Initial Access
Lateral Movement
Persistence
Privilege Escalation
Topic Tags
Description
Nuuo Central Management Server v3.1 and prior use an 8 digit session cookie that could be bruteforced. The application uses a session identification mechanism that could allow attackers to obtain the active session ID, which could allow arbitrary remote code execution.
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Ratings
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Attacker ValueMedium
-
ExploitabilityLow
Technical Analysis
Details
Details from module documentation in Metasploit.
The NUUO CMS protocol uses session tokens in a similar way to HTTP cookies. As mentioned in the summary, if a USERLOGIN request is sent with a correct username and password, a “User-Session-No” token will be returned. The number returned is composed of 8 digits, so if an attacker wanted to guess it, they would have 10 million possibilities, and would be able to bruteforce it on average after 5 million tries.
The function responsible for creating a new user is at offset 0x454E80 in CMS_Server.exe version 2.1. It sets up a new user object and returns the session token to the calling function. This function has what is probably a coding error – the number returned is actually not a number, but the heap address of the user object created by invoking “new()” in the user object class. An assembly snippet is shown below:
.text:00454E80 000 push 0FFFFFFFFh .text:00454E82 004 push offset loc_5E2013 .text:00454E87 008 mov eax, large fs:0 .text:00454E8D 008 push eax .text:00454E8E 00C sub esp, 8 .text:00454E91 014 push ebp .text:00454E92 018 push esi .text:00454E93 01C push edi .text:00454E94 020 mov eax, dword_68D134 .text:00454E99 020 xor eax, esp .text:00454E9B 020 push eax .text:00454E9C 024 lea eax, [esp+24h+var_C] .text:00454EA0 024 mov large fs:0, eax .text:00454EA6 024 mov ebp, ecx .text:00454EA8 024 lea edi, [ebp+43Ch] .text:00454EAE 024 push edi ; lpCriticalSection_EnterCriticalSection .text:00454EAF 028 mov [esp+28h+var_10], edi .text:00454EB3 028 call ds:EnterCriticalSection .text:00454EB9 024 push 1B8h ; unsigned int .text:00454EBE 028 mov [esp+28h+var_4], 0 .text:00454EC6 028 call ??2@YAPAXI@Z ; new() operator, returns object in eax (...)
After the call to ??2@YAPAXI@Z in .text:00454EC6, the session number is returned to the calling function (sub_457100), which then stores it and sends it back to the client as the valid session number:
NUCM/1.0 200 OK User-Valid: %d Server-Version: %s Ini-Version: %d License-Number: %d User-Session-No: %u <---- session number, which is a hexadecimal memory address converted to decimal
These session numbers (tokens) are not that easy to predict, however after collecting thousands of samples I was able to build a table of the most common occurrences, which reduces the possibilities from 10 million to about 1.2 million. In practice, the tokens can usually be guessed between in less than 500,000 attempts – an improvement of 95% over standard bruteforcing. It is likely this can be further improved with some deeper analysis, but due to time constraints this was not investigated further. The tables used to do the bruteforcing are in Appendix #C.
This attack is perfectly feasible despite the high number of attempts needed. Firstly, there is no bruteforce protection on the CMS server, so we can just flood it with requests and find the session number in less than an hour.
Secondly, due to the nature of this application, it is normal to have the software clients logged in for a long amount of time (days, weeks) in order to monitor the video cameras controlled by CMS.
It is worth noticing that when a user logs in, the session has to be maintained by periodically sending a PING request. To bruteforce the session, we send each guess with a PING request until a 200 OK message is received.
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