Detect Taint Shared Content in CrowdStrike LogScale
Adversaries may deliver payloads to remote systems by adding content to shared storage locations, such as network drives or internal code repositories. Content stored on network drives or in other shared locations may be tainted by adding malicious programs, scripts, or exploit code to otherwise valid files. Once a user opens the shared tainted content, the malicious portion can be executed to run the adversary's code on a remote system. Variants include the directory share pivot (planting malicious .LNK files that masquerade as legitimate directories), binary infection (prepending or appending code to legitimate executables on shares), and Office document macro injection (as seen with Gamaredon Group). Threat actors including Conti, Ursnif, Ramsay, InvisiMole, and RedCurl have all leveraged this technique for lateral movement.
MITRE ATT&CK
- Tactic
- Lateral Movement
- Technique
- T1080 Taint Shared Content
- Canonical reference
- https://attack.mitre.org/techniques/T1080/
LogScale Detection Query
// T1080 - Taint Shared Content: Executables, scripts, LNK, or Office macros written to network shares
#event_simpleName = "AsepValueUpdate" OR #event_simpleName = "NewExecutableWritten" OR #event_simpleName = "PeFileWritten" OR #event_simpleName = "SuspiciousFileWrite"
// Alternatively use the broader write events:
| #event_simpleName = /^(NewExecutableWritten|PeFileWritten|SuspiciousFileWrite|GenericFileWrite)$/
// Filter to UNC paths and known share patterns
| TargetFileName = /^(\\\\|[A-Za-z]:\\.*\\(share|shares|public|users|common|docs|dept|data)\\)/i
// Suspicious extensions
| TargetFileName = /\.(exe|dll|scr|bat|cmd|vbs|js|hta|ps1|lnk|docm|xlsm|pptm|doc|xls)$/i
// Exclude known-safe processes
| ImageFileName != /(?i)(MsMpEng\.exe|msiexec\.exe|TrustedInstaller\.exe|wuauclt\.exe|svchost\.exe)$/
// Signal classification
| eval Signal = if(match(TargetFileName, /\.(docm|xlsm|pptm|doc|xls)$/i), "MacroOfficeOnShare",
if(match(TargetFileName, /\.lnk$/i), "LnkOnNetworkShare", "ExecOnNetworkShare"))
// Extract process name from full path
| ProcessName := ImageFileName
| ProcessName = /[^\\]+$/
| match(ProcessName, "value")
| groupBy([ComputerName, UserName, Signal, TargetFileName, ImageFileName, CommandLine], function=[
count(aid, as=EventCount),
max(ContextTimeStamp, as=LastSeen),
min(ContextTimeStamp, as=FirstSeen)
])
| sort(LastSeen, order=desc)
| select([LastSeen, FirstSeen, ComputerName, UserName, Signal, TargetFileName, ImageFileName, CommandLine, EventCount])CrowdStrike LogScale (Falcon) query detecting T1080 Taint Shared Content using Falcon telemetry for executable, script, LNK, and macro-enabled Office file writes to UNC network paths or mapped shared directories. Aggregates events per host/user/file for deduplication and groups by signal variant (ExecOnNetworkShare, LnkOnNetworkShare, MacroOfficeOnShare).
Data Sources
Required Tables
False Positives & Tuning
- Patch management or endpoint management platforms (Tanium, BigFix) that push executable updates to hosts via network share-based distribution
- Development teams with CI/CD pipelines that write compiled binaries to shared NAS/SAN locations as part of internal artifact distribution
- Power users legitimately creating .lnk shortcut files pointing to network share application launchers as part of desktop shortcut management
Other platforms for T1080
Testing Methodology
Validate this detection against 4 adversary techniques from Atomic Red Team. Each test below lists the behaviour to exercise and the telemetry you should expect to see. Executable commands and cleanup steps are available with Pro.
- Test 1Copy Malicious Executable to Network Share (Conti/Ursnif Pattern)
Expected signal: Sysmon Event ID 11: TargetFilename=\\localhost\C$\Users\Public\svchost_update.exe, Image=cmd.exe or robocopy.exe/xcopy.exe. Sysmon Event ID 3: Network connection to localhost:445 from cmd.exe. Security Event ID 5145 on the target host: RelativeTargetName=Users\Public\svchost_update.exe, AccessMask including write/create. Security Event ID 5140: share \\*\C$ accessed.
- Test 2Plant Malicious LNK File on Network Share (Directory Share Pivot)
Expected signal: Sysmon Event ID 11: TargetFilename=\\localhost\C$\Users\Public\Shared Documents.lnk, Image=powershell.exe. DeviceFileEvents: FileName=Shared Documents.lnk, FolderPath=\\localhost\C$\Users\Public\, ActionType=FileCreated. If a user clicks the .LNK: Sysmon Event ID 1 with Image=cmd.exe, CommandLine containing the embedded payload, ParentImage=explorer.exe.
- Test 3Inject Macro into Office Document on Network Share (Gamaredon Pattern)
Expected signal: Sysmon Event ID 11: TargetFilename=\\localhost\C$\Users\Public\Q1_Budget_Review.docm, Image=powershell.exe. DeviceFileEvents: FileName=Q1_Budget_Review.docm, FolderPath starts with \\, ActionType=FileCreated. Security Event 5145 with RelativeTargetName=Users\Public\Q1_Budget_Review.docm and write access.
- Test 4Bulk Executable Spreading Across Multiple Shares (Worm Propagation Simulation)
Expected signal: Two Sysmon Event ID 11 entries: both with Image=cmd.exe and TargetFilename pointing to separate UNC share paths. Two Security Event 5145 entries on localhost for write to .exe on each share. DeviceFileEvents: two FileCreated events with distinct FolderPath values (different share names) from the same InitiatingProcessFileName within seconds.
References (10)
- https://attack.mitre.org/techniques/T1080/
- https://rewtin.blogspot.ch/2017/11/abusing-user-shares-for-efficient.html
- https://www.group-ib.com/resources/threat-research/red-curl.html
- https://www.welivesecurity.com/2020/06/11/gamaredon-group-grows-its-game/
- https://www.welivesecurity.com/2020/05/13/ramsay-cyberespionage-toolkit-airgapped-networks/
- https://www.cybereason.com/blog/conti-ransomware
- https://www.secureworks.com/research/bronze-butler-targets-japanese-businesses
- https://docs.microsoft.com/en-us/windows/security/threat-protection/auditing/event-5145
- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1080/T1080.md
- https://learn.microsoft.com/en-us/defender-endpoint/advanced-hunting-devicefileevents-table
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