SparrowDoor
SparrowDoor is a custom backdoor associated with the China-linked espionage group FamousSparrow. Reporting describes it as the group’s main or flagship backdoor and attributes its use against hotels worldwide as well as government, international organization, engineering, law firm, and other entities in countries including Brazil, Burkina Faso, South Africa, Canada, Israel, France, Guatemala, Lithuania, Saudi Arabia, Taiwan, Thailand, the United Kingdom, and, in later activity, Mexico, Argentina, Chile, Ecuador, Honduras, and Panama. ESET assessed FamousSparrow exploited vulnerable internet-facing applications, including Microsoft Exchange ProxyLogon, Microsoft SharePoint, and Oracle Opera hotel-management software, to deploy SparrowDoor; later reporting also states FamousSparrow likely exploited ProxyLogon flaws in Microsoft Exchange Server to deploy it in 2025 campaigns.
SparrowDoor is staged via DLL search-order hijacking using the legitimate K7 Computing executable Indexer.exe, a malicious K7UI.dll, and an encrypted shellcode file MpSvc.dll, with staging files dropped in %PROGRAMDATA%\Software. K7UI.dll patches Indexer.exe execution flow, loads and decrypts MpSvc.dll, and executes shellcode that rebuilds and launches an in-memory backdoor image lacking PE headers. Persistence is established via a registry Run key and a Windows service using hardcoded configuration data. SparrowDoor uses command-line arguments including -i, -k, and -d to control execution flow.
Capabilities directly described in the source material include collecting host and system information, communicating with a C2 domain over HTTPS on port 443, attempting direct connection before falling back to proxy settings, file and directory operations, file exfiltration, process creation with stolen tokens, shellcode injection, and command execution through cmd.exe. It can provide an interactive reverse shell using named pipes for I/O and enables SeDebugPrivilege by adjusting its process token. Configuration is decrypted with XOR key ^&32yUgf and includes the C2 domain credits.offices-analytics[.]com; outbound data is XOR-encrypted with key hH7@83#mi and inbound data decrypted with key h*^4hFa.
The content also notes that CrowDoor is a variant of SparrowDoor, and TernDoor is described as a variant of CrowDoor, indicating SparrowDoor as the root of a related backdoor lineage used in later China-linked intrusions.
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Vulnerabilities exploited
1 CVE Mallory has correlated with this family across public research and vendor advisories. Each row links to the full Mallory page for that vulnerability.
"...a detailed technical analysis of the group’s main backdoor that we have named SparrowDoor."
Groups observed using it
3 distinct threat actors attributed by public researchers. Open in Mallory to see the full evidence chain and overlapping campaigns.
TAG-141 (FamousSparrow) leveraged SparrowDoor malware against entities in Mexico, Argentina, and Chile.
TAG-141 (FamousSparrow) leveraged SparrowDoor malware against entities in Mexico, Argentina, and Chile.
CrowDoor is a variant of SparrowDoor, another backdoor attributed to FamousSparrow.
IOCs tracked for this family
6 indicators attributed across vendor reports, sandbox runs, and researcher write-ups. Full values are available in Mallory.
IPs, domains, and DNS infrastructure linked to this family.
File hashes (MD5, SHA-1, SHA-256) from samples and reports.
Recent activity
6 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
Malware used by TAG-141 (FamousSparrow) against entities in multiple LAC countries.
Referenced as the parent backdoor family in the lineage described (Crowdoor is a variant of SparrowDoor); no additional capabilities described in the provided content.
Backdoor family referenced as the parent lineage for CrowDoor; attributed in the content to Famous Sparrow.
Backdoor used by the Chinese threat actor FamousSparrow in attacks on U.S. and Mexican organizations.
The version that knows your environment.
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CVEs this family uses for access and lateral movement.
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Reddit, Mastodon, and CTI community discussion around this family.