Potential Build Process Compromise

Original query, unchanged.

// How far back to look for events from
let timeframe = 1d;
// How close together build events and file modifications should occur to alert (make this smaller to reduce FPs)
let time_window = 5m;
// Edit this to include build processes used
let build_processes = dynamic(["MSBuild.exe", "dotnet.exe", "VBCSCompiler.exe"]);
// Include any processes that you want to allow to edit files during/around the build process
let allow_list = dynamic([""]);
(union isfuzzy=true
(SecurityEvent
| where TimeGenerated > ago(timeframe)
// Look for build process starts
| where EventID == 4688
| where Process has_any (build_processes)
| summarize by BuildParentProcess=ParentProcessName, BuildProcess=Process, BuildAccount = Account, Computer, BuildCommand=CommandLine, timekey= bin(TimeGenerated, time_window), BuildProcessTime=TimeGenerated
| join kind=inner(
SecurityEvent
| where TimeGenerated > ago(timeframe)
// Look for file modifications to code file
| where EventID == 4663
| where Process !in (allow_list)
// Look for code files, edit this to include file extensions used in build.
| where ObjectName endswith ".cs" or ObjectName endswith ".cpp"
// 0x6 and 0x4 for file append, 0x100 for file replacements
| where AccessMask == "0x6"  or AccessMask == "0x4" or AccessMask == "0X100"
| summarize by FileEditParentProcess=ParentProcessName, FileEditAccount = Account, Computer, FileEdited=ObjectName, FileEditProcess=ProcessName, timekey= bin(TimeGenerated, time_window), FileEditTime=TimeGenerated)
// join where build processes and file modifications seen at same time on same host
on timekey, Computer
// Limit to only where the file edit happens after the build process starts
| where BuildProcessTime <= FileEditTime
| summarize make_set(FileEdited), make_set(FileEditProcess), make_set(FileEditAccount) by timekey, Computer, BuildParentProcess, BuildProcess
),
(WindowsEvent
| where TimeGenerated > ago(timeframe)
// Look for build process starts
| where EventID == 4688 and EventData has_any (build_processes)
| extend NewProcessName = tostring(EventData.NewProcessName)
| extend Process=tostring(split(NewProcessName, '\\')[-1])
| where Process has_any (build_processes)
| extend ParentProcessName = tostring(EventData.ParentProcessName)
| extend Account =  strcat(tostring(EventData.SubjectDomainName),"\\", tostring(EventData.SubjectUserName))
| extend CommandLine = tostring(EventData.CommandLine) 
| summarize by BuildParentProcess=ParentProcessName, BuildProcess=Process, BuildAccount = Account, Computer, BuildCommand=CommandLine, timekey= bin(TimeGenerated, time_window), BuildProcessTime=TimeGenerated
| join kind=inner(
WindowsEvent
| where TimeGenerated > ago(timeframe)
// Look for file modifications to code file
| where EventID == 4663 and EventData has_any ("0x6", "0x4", "0X100") and EventData has_any (".cs", ".cpp")
| extend NewProcessName = tostring(EventData.NewProcessName)
| extend Process=tostring(split(NewProcessName, '\\')[-1])
| where Process !in (allow_list)
// Look for code files, edit this to include file extensions used in build.
| extend ObjectName = tostring(EventData.ObjectName)
| where ObjectName endswith ".cs" or ObjectName endswith ".cpp"
// 0x6 and 0x4 for file append, 0x100 for file replacements
| extend AccessMask = tostring(EventData.AccessMask)  
| where AccessMask == "0x6"  or AccessMask == "0x4" or AccessMask == "0X100"
| extend ParentProcessName = tostring(EventData.ParentProcessName)
| extend Account =  strcat(tostring(EventData.SubjectDomainName),"\\", tostring(EventData.SubjectUserName))
| extend ProcessName = tostring(EventData.ProcessName)
| summarize by FileEditParentProcess=ParentProcessName, FileEditAccount = Account, Computer, FileEdited=ObjectName, FileEditProcess=ProcessName, timekey= bin(TimeGenerated, time_window), FileEditTime=TimeGenerated)
// join where build processes and file modifications seen at same time on same host
on timekey, Computer
// Limit to only where the file edit happens after the build process starts
| where BuildProcessTime <= FileEditTime
| summarize make_set(FileEdited), make_set(FileEditProcess), make_set(FileEditAccount) by timekey, Computer, BuildParentProcess, BuildProcess
))
| extend HostName = tostring(split(Computer, ".")[0]), DomainIndex = toint(indexof(Computer, '.'))
| extend HostNameDomain = iff(DomainIndex != -1, substring(Computer, DomainIndex + 1), Computer)
| project-away DomainIndex