Gen Digital published research this week documenting an active campaign by the China-linked intrusion set tracked as UNC3569, in which the group exploited a security flaw in Sogou Input Method — one of the most widely deployed Chinese-language input method editors (IMEs) on Windows — to deliver a previously undocumented backdoor dubbed GRAYRABBIT. The intrusion chain is deceptively simple: a crafted link delivered to the victim initiates exploitation, and by the end of the chain the attacker holds the full privilege set of the logged-in user. On a typical enterprise workstation, that means access to email, files, browser sessions, saved credentials, and anything else the user can reach.
This campaign matters to defenders well beyond organizations with Chinese-speaking user bases. IMEs are deeply privileged components of the Windows text-input stack, they auto-update over the network, they ship bundled with OEM images, and they are frequently installed by employees without IT approval. Tencent, which owns Sogou, distributes the software to hundreds of millions of users. Any product with that footprint and that level of OS integration is an attractive initial-access surface — and UNC3569 has now demonstrated operational capability against it in the wild. If Sogou Input Method exists anywhere in your environment, treat this as an active-exploitation event and act accordingly.
Technical Analysis
Affected product and platform
- Product: Sogou Input Method (搜狗输入法), owned and distributed by Tencent
- Platform: Microsoft Windows (the IME is primarily a Windows desktop product)
- Component class: Input Method Editor — a Text Services Framework (TSF) client that loads into user processes to handle Chinese character composition
No CVE identifier has been publicly assigned to the exploited flaw at the time of writing, and Gen Digital's reporting does not reference one. Defenders should monitor Tencent/Sogou advisories and the CISA Known Exploited Vulnerabilities catalog for a formal assignment — active, confirmed in-the-wild exploitation makes KEV inclusion a realistic near-term outcome.
Why IMEs are a high-value target
Input method editors occupy a uniquely dangerous position in the Windows architecture. An IME is not a sandboxed app — it is code that loads into the context of applications accepting text input, communicates with cloud services for prediction and updates, and historically has been a reliable source of privilege escalation and code-execution bugs. Sogou's IME in particular has a documented history of security scrutiny around its updater and encryption implementation. Key characteristics that make this attack surface attractive to an APT operator:
- Ubiquity in target populations: Any organization with employees who type Chinese — including diaspora communities, academics, journalists, and business users — likely has Sogou installed, often outside of managed software inventories.
- Deep OS integration: The IME framework loads DLLs into interactive processes, providing ample opportunity for a compromised IME component to execute code in the user's context.
- Trusted network posture: IME processes routinely beacon to vendor cloud infrastructure for updates and prediction services, giving malicious traffic from an IME-adjacent process a veneer of legitimacy against naive egress filtering.
- Auto-update channels: A network-facing update mechanism on an endpoint is a direct path from the internet to code execution — exactly the class of flaw UNC3569 exploited.
Attack chain (defender's view)
Based on Gen Digital's published research, the intrusion unfolds as follows:
- Initial access — crafted link. The victim is lured to a weaponized URL (delivery vector consistent with spearphishing or watering-hole-style targeting). This is the one user-interaction step in the chain; defenders should treat unexpected link-click telemetry followed by IME process anomalies as high-fidelity correlation.
- Exploitation of the Sogou Input Method flaw. The crafted content triggers the vulnerability in the Sogou IME component. Exploitation yields code execution without requiring the victim to run an obvious executable — the Sogou process tree is where defenders should focus.
- GRAYRABBIT deployment. The attacker stages and installs the GRAYRABBIT backdoor on the host. As a persistent implant, GRAYRABBIT will exhibit the standard backdoor behaviors: a persistence mechanism (registry Run key, scheduled task, or service), outbound C2 communications, and command-handling capability.
- Full user-context control. Gen Digital's assessment is blunt: the attacker can do anything the logged-in user can do. That includes reading and exfiltrating user-accessible data, hijacking authenticated sessions, staging credential theft, and pivoting to other systems reachable with the user's privileges.
Exploitation status
- Confirmed active exploitation in the wild — this is not a theoretical or proof-of-concept scenario. Gen Digital attributes real intrusions to UNC3569 using this chain.
- Attribution: China-linked threat cluster UNC3569 (UNC designations indicate activity not yet merged into a named APT group — treat as a capable, state-nexus-aligned operator).
- CVE / KEV: None assigned or listed as of publication. Monitor CISA KEV and vendor advisories.
Detection & Response
The detections below are built around the observable mechanics of this campaign: abnormal process lineage under Sogou IME components, child-process execution spawned by the IME, persistence artifacts consistent with a newly implanted backdoor, and network egress from input-method processes to non-vendor infrastructure. They are deliberately scoped to behaviors that a legitimate IME should rarely if ever exhibit — tune the allowlists to your environment before broad deployment.
Sigma Rules
---
title: Sogou Input Method Process Spawning Shell or Script Interpreter
id: 8f3a2c71-5b6d-4e9a-bc14-7d2e9f013456
status: experimental
description: Detects Sogou IME components spawning command shells, script interpreters, or LOLBins — consistent with UNC3569 exploitation of the Sogou Input Method flaw to execute code and stage the GRAYRABBIT backdoor.
references:
- https://thehackernews.com/2026/09/china-linked-unc3569-exploited-sogou.html
- https://attack.mitre.org/techniques/T1059/
author: Security Arsenal
date: 2026/09/25
tags:
- attack.execution
- attack.t1059
- attack.initial_access
- attack.t1189
logsource:
category: process_creation
product: windows
detection:
selection_parent:
ParentImage|contains:
- '\SogouInput\'
- '\Sogou\'
ParentImage|endswith:
- '\SGTool.exe'
- '\SogouCloud.exe'
- '\SogouExplorer.exe'
- '\PicFace.exe'
- '\SGImeBro.exe'
selection_child:
Image|endswith:
- '\cmd.exe'
- '\powershell.exe'
- '\pwsh.exe'
- '\wscript.exe'
- '\cscript.exe'
- '\mshta.exe'
- '\rundll32.exe'
- '\regsvr32.exe'
- '\wmic.exe'
- '\bitsadmin.exe'
- '\certutil.exe'
condition: selection_parent and selection_child
falsepositives:
- Sogou self-update operations invoking system utilities (verify against vendor update windows and signed child processes)
level: high
---
title: GRAYRABBIT-Style Persistence via Run Key or Scheduled Task from Non-Standard Binary
id: 2c7e91b4-4a8f-4d3c-9e21-6b0a5d8f2347
status: experimental
description: Detects registry Run-key or scheduled-task persistence registered by executables in user-writable or anomalous paths shortly after a browser or IME process execution — behavior consistent with backdoor installation following drive-by exploitation such as the UNC3569 GRAYRABBIT campaign.
references:
- https://thehackernews.com/2026/09/china-linked-unc3569-exploited-sogou.html
- https://attack.mitre.org/techniques/T1547/001/
- https://attack.mitre.org/techniques/T1053/005/
author: Security Arsenal
date: 2026/09/25
tags:
- attack.persistence
- attack.t1547.001
- attack.t1053.005
logsource:
category: registry_set
product: windows
detection:
selection_key:
TargetObject|contains:
- '\CurrentVersion\Run\'
- '\CurrentVersion\RunOnce\'
selection_value:
Details|contains:
- '\AppData\'
- '\Temp\'
- '\ProgramData\'
- '\Users\Public\'
filter_known_good:
Details|contains:
- '\AppData\Local\Microsoft\'
- 'OneDrive.exe'
- 'Teams.exe'
condition: selection_key and selection_value and not filter_known_good
falsepositives:
- Legitimate per-user application installers registering auto-start entries
level: medium
---
title: Network Connection from Sogou IME Process to Non-Vendor Destination
id: 6d1b4a92-7c3e-4f58-a902-9e3c7b516d08
status: experimental
description: Detects Sogou Input Method processes establishing outbound connections to destinations outside known Sogou/Tencent infrastructure — potentially indicating C2 traffic from a compromised IME component or a GRAYRABBIT implant masquerading under the IME process context.
references:
- https://thehackernews.com/2026/09/china-linked-unc3569-exploited-sogou.html
- https://attack.mitre.org/techniques/T1071/001/
author: Security Arsenal
date: 2026/09/25
tags:
- attack.command_and_control
- attack.t1071.001
logsource:
category: network_connection
product: windows
detection:
selection:
Image|contains:
- '\SogouInput\'
- '\Sogou\'
Initiated: 'true'
filter_rfc1918:
DestinationIp|cidr:
- '10.0.0.0/8'
- '172.16.0.0/12'
- '192.168.0.0/16'
filter_loopback:
DestinationIp|startswith:
- '127.'
condition: selection and not filter_rfc1918 and not filter_loopback
falsepositives:
- Sogou cloud prediction, dictionary sync, and update services (baseline vendor domains/ASNs and exclude before production deployment)
level: medium
The first rule is the highest-fidelity of the three: a Chinese IME has essentially no legitimate reason to spawn cmd.exe, PowerShell, or mshta.exe. The second rule is intentionally broader — it will require allowlisting of common per-user auto-updaters in your environment — but it catches the persistence stage of GRAYRABBIT-class implants regardless of which IME or browser delivered them. The third rule is a hunting rule: baseline Sogou's legitimate cloud endpoints first, then alert on deviations.
KQL (Microsoft Sentinel / Defender)
// Hunt 1: Sogou IME processes spawning interpreters or LOLBins (UNC3569 exploitation behavior)
DeviceProcessEvents
| where TimeGenerated > ago(14d)
| where InitiatingProcessFolderPath has_any ("SogouInput", "Sogou")
or InitiatingProcessFileName in~ ("SGTool.exe", "SogouCloud.exe", "SogouExplorer.exe", "SGImeBro.exe")
| where FileName in~ ("cmd.exe", "powershell.exe", "pwsh.exe", "wscript.exe", "cscript.exe",
"mshta.exe", "rundll32.exe", "regsvr32.exe", "wmic.exe", "bitsadmin.exe", "certutil.exe")
| project TimeGenerated, DeviceName, AccountName, InitiatingProcessFileName, InitiatingProcessCommandLine,
FileName, ProcessCommandLine, SHA256, ReportId
| order by TimeGenerated desc;
// Hunt 2: New persistence registration referencing user-writable paths, correlated with recent browser/IME activity
DeviceRegistryEvents
| where TimeGenerated > ago(14d)
| where RegistryKey has_any ("\\CurrentVersion\\Run", "\\CurrentVersion\\RunOnce")
| where RegistryValueData has_any ("\\AppData\\", "\\Temp\\", "\\ProgramData\\", "\\Users\\Public\\")
| where RegistryValueData !has_any ("OneDrive.exe", "Teams.exe", "Microsoft\\")
| project TimeGenerated, DeviceName, InitiatingProcessFileName, InitiatingProcessFolderPath,
RegistryKey, RegistryValueName, RegistryValueData
| order by TimeGenerated desc;
// Hunt 3: Rare external destinations contacted by Sogou processes (C2 hunting — baseline first)
DeviceNetworkEvents
| where TimeGenerated > ago(30d)
| where InitiatingProcessFolderPath has_any ("SogouInput", "Sogou")
| where RemoteIPType == "Public"
| summarize Connections = count(), FirstSeen = min(TimeGenerated), LastSeen = max(TimeGenerated),
Devices = dcount(DeviceId)
by RemoteUrl, RemoteIP, InitiatingProcessFileName
| where Connections < 50 // surface low-prevalence destinations; tune after baselining vendor endpoints
| order by FirstSeen asc;
Run Hunt 3 as a baseline exercise before treating its output as alerts — Sogou legitimately beacons to Tencent cloud infrastructure, and the value of the query is in surfacing rare destinations. Low-prevalence, recently-seen external endpoints contacted by an IME process are exactly where a GRAYRABBIT C2 channel would hide.
Velociraptor VQL
-- Hunt: Identify Sogou IME installations and suspicious child processes / unsigned binaries in IME-adjacent paths
SELECT Pid,
Ppid,
Name,
Exe,
CommandLine,
Username,
CreateTime,
authenticode(filename=Exe) AS Signature
FROM pslist()
WHERE Exe =~ '(?i)Sogou'
OR CommandLine =~ '(?i)SogouInput'
-- Hunt: Unsigned or recently-created executables in user-writable paths (GRAYRABBIT staging locations)
SELECT FullPath,
Size,
Mtime,
Ctime,
authenticode(filename=FullPath) AS Signature
FROM glob(globs=['C:/Users/*/AppData/**/*.exe',
'C:/ProgramData/**/*.exe',
'C:/Users/Public/**/*.exe'])
WHERE Ctime > ago('72h')
AND (Signature.Trusted != 'trusted' OR Signature.SubjectName =~ '(?i)sogou|tencent')
ORDER BY Ctime DESC
-- Hunt: Live network connections held by Sogou-related processes (identify active C2)
SELECT Pid,
Name,
Status,
Laddr,
Raddr,
CommandLine
FROM netstat()
WHERE Name =~ '(?i)SGTool|SogouCloud|SogouExplorer|SGImeBro'
OR CommandLine =~ '(?i)Sogou'
Remediation & Verification Script (PowerShell)
The following script inventories Sogou installations, captures running IME processes and their network connections for triage, and — when run with -Quarantine — terminates Sogou processes and disables their auto-start entries pending vendor patching. Review before running in production; the quarantine path will disrupt Chinese-language input for affected users, so coordinate with the business first.
# UNC3569 / Sogou Input Method — Inventory, Triage, and Optional Quarantine
# Run elevated. Use -Quarantine only after business approval (disables Chinese IME).
param(
[switch]$Quarantine,
[string]$OutputPath = "C:\IR\SogouTriage_$(Get-Date -Format 'yyyyMMdd_HHmmss')"
)
New-Item -ItemType Directory -Path $OutputPath -Force | Out-Null
Write-Host "[+] Output directory: $OutputPath"
# 1. Inventory installed Sogou components (registry uninstall keys)
Write-Host "[+] Enumerating installed Sogou software..."
$installed = Get-ItemProperty "HKLM:\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\*",
"HKLM:\SOFTWARE\WOW6432Node\Microsoft\Windows\CurrentVersion\Uninstall\*",
"HKCU:\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\*" -ErrorAction SilentlyContinue |
Where-Object { $_.DisplayName -match 'Sogou|搜狗' } |
Select-Object DisplayName, DisplayVersion, InstallLocation, Publisher
$installed | Export-Csv "$OutputPath\installed_sogou.csv" -NoTypeInformation
$installed | Format-Table -AutoSize
# 2. Capture running Sogou processes and their network connections
Write-Host "[+] Capturing running Sogou processes and connections..."
$sogouProcs = Get-Process | Where-Object { $_.Path -match 'Sogou' -or $_.Name -match 'SGTool|SogouCloud|SGImeBro' }
$sogouProcs | Select-Object Id, Name, Path, StartTime |
Export-Csv "$OutputPath\sogou_processes.csv" -NoTypeInformation
foreach ($p in $sogouProcs) {
Get-NetTCPConnection -OwningProcess $p.Id -ErrorAction SilentlyContinue |
Select-Object OwningProcess, LocalAddress, LocalPort, RemoteAddress, RemotePort, State |
Export-Csv "$OutputPath\sogou_connections_$($p.Id).csv" -NoTypeInformation
}
# 3. Enumerate persistence entries pointing at Sogou or user-writable paths
Write-Host "[+] Checking Run keys for suspicious auto-start entries..."
$runKeys = @("HKLM:\SOFTWARE\Microsoft\Windows\CurrentVersion\Run",
"HKCU:\SOFTWARE\Microsoft\Windows\CurrentVersion\Run",
"HKLM:\SOFTWARE\WOW6432Node\Microsoft\Windows\CurrentVersion\Run")
foreach ($key in $runKeys) {
Get-ItemProperty $key -ErrorAction SilentlyContinue |
ForEach-Object { $_.PSObject.Properties } |
Where-Object { $_.Value -match 'Sogou|AppData|ProgramData|Users\\Public' } |
Select-Object @{n='Key';e={$key}}, Name, Value |
Export-Csv "$OutputPath\autoruns_suspicious.csv" -Append -NoTypeInformation
}
# 4. Optional quarantine: kill Sogou processes and disable auto-start
if ($Quarantine) {
Write-Warning "[-Quarantine] Terminating Sogou processes and removing Run-key entries..."
$sogouProcs | Stop-Process -Force -ErrorAction SilentlyContinue
foreach ($key in $runKeys) {
$props = Get-ItemProperty $key -ErrorAction SilentlyContinue
foreach ($prop in $props.PSObject.Properties) {
if ($prop.Value -match 'Sogou|搜狗') {
Write-Host " Removing $($prop.Name) from $key"
Remove-ItemProperty -Path $key -Name $prop.Name -ErrorAction SilentlyContinue
}
}
}
Write-Host "[+] Quarantine complete. Reboot and re-verify."
}
Write-Host "[+] Triage complete. Review CSVs in $OutputPath"
Remediation
- Inventory first. Most organizations do not know whether Sogou Input Method is installed. Use the PowerShell script above, your EDR software inventory, or your asset-management platform to enumerate it. Include per-user (HKCU) installations — IMEs frequently install without administrative rights.
- Patch or remove. Apply the fixed Sogou Input Method build from the official Tencent/Sogou distribution channel as soon as it is available — verify the version against Tencent's security advisory at the official Sogou site (shurufa.sogou.com) and confirm update integrity, given the attack's abuse of the software's trusted posture. Where Chinese input is not a business requirement, uninstall the IME entirely — removal is the only remediation that fully closes this attack surface, and Windows ships a built-in Microsoft Pinyin IME that covers legitimate Chinese-input needs without third-party exposure.
- Block the delivery vector. The chain begins with a crafted link. Enforce URL rewriting/detonation in email (e.g., Microsoft Defender Safe Links or equivalent), apply browser isolation for uncategorized domains, and confirm your secure web gateway is blocking newly registered domains for targeted user populations.
- Constrain the blast radius. Because GRAYRABBIT operates with the logged-in user's full privileges, least-privilege hygiene is a direct mitigation: remove local admin from standard users, enforce LAPS-managed local admin passwords, and ensure sensitive data access is segmented so a single compromised user context cannot reach crown-jewel shares.
- Hunt retroactively. Run the KQL hunts above across at least 30 days of telemetry on any host where Sogou was present. Look specifically for IME-spawned child processes, new Run-key entries, and rare external destinations contacted by Sogou binaries. If any hits are confirmed, treat the host as compromised: isolate, acquire memory and disk, and rotate the affected user's credentials — including any sessions and tokens, since a user-context backdoor can replay them.
- Monitor for formal identifiers. Track the CISA Known Exploited Vulnerabilities catalog, Gen Digital's published research, and Tencent advisories for a CVE assignment and patch-specific deadlines. If KEV-listed, CISA Binding Operational Directive timelines will apply to federal civilian agencies and are a sensible internal SLA benchmark for everyone else.
- Policy hardening going forward. Add third-party IMEs to your software-approval workflow. IMEs, system utilities, and "productivity" tools from vendors outside your normal procurement vetting are recurring initial-access surfaces — this campaign is the second recent reminder that language-input software sits squarely in APT targeting logic for specific demographic and community targeting.
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