Detect Exfiltration Over Symmetric Encrypted Non-C2 Protocol in CrowdStrike LogScale
Adversaries may steal data by exfiltrating it over a symmetrically encrypted network protocol other than that of the existing command and control channel. Symmetric encryption algorithms (RC4, AES, ChaCha20, Blowfish) use shared keys on both ends of the channel. Attackers may implement custom encryption over protocols not natively encrypted (HTTP, FTP, DNS) or add extra encryption layers over already-encrypted protocols (HTTPS, SFTP) to obscure data contents from network inspection tools. This technique is distinguished from asymmetric exfiltration by the pre-shared key requirement, often resulting in artifacts such as key material embedded in scripts, configuration files, or command-line arguments.
MITRE ATT&CK
- Tactic
- Exfiltration
- Sub-technique
- T1048.001 Exfiltration Over Symmetric Encrypted Non-C2 Protocol
- Canonical reference
- https://attack.mitre.org/techniques/T1048/001/
LogScale Detection Query
// Detection 1: ProcessRollup2 — encryption tool with cipher args and network target indicators
#event_simpleName=ProcessRollup2
| FileName = /(?i)(openssl|ccrypt|mcrypt|cryptcat|aescrypt|gpg)/
OR (FileName = /(?i)python/ AND CommandLine = /(?i)(AES|RC4|Cipher|encrypt|socket|send|pycrypto|cryptography)/)
| CommandLine = /(?i)(enc[\s]+-aes|enc[\s]+-rc4|-aes-256|-aes-128|aes256|aes128|-rc4|arcfour|chacha20|-nosalt|-pass[\s]+pass:|-passout|-passin|-k[\s]+\S+)/
| CommandLine = /(?i)(-connect|netcat|nc[\s]|curl|wget|ftp:\/\/|http:\/\/|https:\/\/|tcp|socket|[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3})/
| EncryptionAlgo := if(CommandLine = /(?i)aes/, "AES",
if(CommandLine = /(?i)(rc4|arcfour)/, "RC4",
if(CommandLine = /(?i)chacha/, "ChaCha20",
if(CommandLine = /(?i)\bdes\b/, "DES", "Unknown"))))
| HasKeyMaterial := if(CommandLine = /(?i)(-k[\s]|-pass[\s]+pass:|-passout|-passin|passphrase|shared.?key)/, "true", "false")
| HasNoSalt := if(CommandLine = /-nosalt/, "true", "false")
| HasNetworkTarget := if(CommandLine = /(?i)(-connect|netcat|nc[\s]|curl|wget|http|socket|tcp)/, "true", "false")
| groupBy(
[ComputerName, UserName, FileName, CommandLine, ParentBaseFileName, EncryptionAlgo, HasKeyMaterial, HasNoSalt, HasNetworkTarget],
function=[
count(as=EventCount),
min(field=ContextTimeStamp, as=FirstSeen),
max(field=ContextTimeStamp, as=LastSeen)
]
)
| sort(field=EventCount, order=desc)
// Detection 2 (run separately): NetworkConnectIP4 — large outbound transfer from encryption process
// #event_simpleName=NetworkConnectIP4
// | RemoteAddressIP4 != /^(10\.|172\.(1[6-9]|2[0-9]|3[01])\.|192\.168\.|127\.)/
// | join(
// [#event_simpleName=ProcessRollup2
// | FileName = /(?i)(openssl|ccrypt|mcrypt|cryptcat|aescrypt|gpg)/],
// field=[TargetProcessId, ComputerName],
// include=[FileName, CommandLine, UserName, ParentBaseFileName]
// )
// | where BytesSent > 1000000
// | ExfilSizeMB := round(BytesSent / 1048576, 2)
// | groupBy([ComputerName, UserName, FileName, RemoteAddressIP4, RemotePort, ExfilSizeMB, CommandLine])
// | sort(field=ExfilSizeMB, order=desc)CrowdStrike LogScale CQL querying ProcessRollup2 events for encryption tool executions (openssl, ccrypt, mcrypt, cryptcat, gpg, aescrypt, Python with crypto imports) bearing symmetric cipher arguments and network connectivity indicators. Uses inline conditional field derivation to classify encryption algorithm (AES/RC4/ChaCha20/DES), key material presence, -nosalt flag, and network target. A second commented query joins NetworkConnectIP4 events to identify large outbound transfers (>1 MB) directly attributable to encryption tool processes on public IPs. Both detections align with the KQL/SPL behavioral scope for T1048.001.
Data Sources
Required Tables
False Positives & Tuning
- Security engineers using openssl for TLS debugging, certificate pinning validation, or cipher suite enumeration on authorized endpoints
- Python-based DevOps tooling using AES-CBC encrypted payloads for secrets management integrations (HashiCorp Vault, AWS KMS) with external endpoints
- Automated backup scripts invoking ccrypt or gpg to encrypt files before transferring to remote SFTP or cloud storage destinations
- Software package managers or update mechanisms that GPG-verify signed packages downloaded from vendor mirrors over HTTPS
Other platforms for T1048.001
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 1Exfiltrate File Using OpenSSL AES Encryption over HTTP
Expected signal: Sysmon Event ID 1: Process Create for openssl with CommandLine containing 'enc -aes-256-cbc -nosalt -k' and the key material. Sysmon Event ID 1: Process Create for curl with destination URL. Sysmon Event ID 3: Network connection from curl to destination IP:8080. Sysmon Event ID 11: File Create for /tmp/exfil_payload.enc. Auditd records showing execve syscalls for openssl and curl with full argument lists.
- Test 2Symmetric Encrypted Exfiltration via Python Script with RC4
Expected signal: Sysmon Event ID 1: Process Create for python3 with CommandLine containing 'rc4', 'socket', 'encrypt', and 'connect'. Sysmon Event ID 3: Network connection from python3 to 192.168.1.200:9001 (non-standard port, high-confidence exfiltration indicator). Auditd execve syscall with full Python -c command argument.
- Test 3OpenSSL Encrypted Data Transfer via Named Pipe to Netcat
Expected signal: Sysmon Event ID 1: Process Create for openssl with '-aes-256-cbc -k <key> -nosalt' in CommandLine. Sysmon Event ID 1: Process Create for nc targeting 192.168.1.200:4444 (classic reverse shell port). Sysmon Event ID 3: Network connection from nc to external IP on port 4444. Possible Sysmon Event ID 1 for tar as parent/sibling process. Linux auditd: execve records for all three commands (tar, openssl, nc).
- Test 4Exfiltration via OpenSSL s_client Over HTTPS Port with Symmetric Key
Expected signal: Sysmon Event ID 1: First openssl process with 'enc -aes-256-cbc -k TeamPreSharedKey99 -nosalt' in CommandLine. Sysmon Event ID 1: Second openssl process with 's_client -connect 192.168.1.200:443' in CommandLine. Sysmon Event ID 3: Network connection from openssl s_client to port 443. Sysmon Event ID 11: File Create for /tmp/inner_encrypted.bin. The double-process pattern (enc then s_client) is highly distinctive.
References (10)
- https://attack.mitre.org/techniques/T1048/001/
- https://arxiv.org/ftp/arxiv/papers/1408/1408.1136.pdf
- https://www.openssl.org/docs/man3.0/man1/openssl-enc.html
- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1048.001/T1048.001.md
- https://www.sans.org/white-papers/33649/
- https://www.mandiant.com/resources/blog/targeted-attack-exfiltration
- https://learn.microsoft.com/en-us/defender-endpoint/advanced-hunting-devicenetworkevents-table
- https://docs.microsoft.com/en-us/sysinternals/downloads/sysmon
- https://github.com/SigmaHQ/sigma/tree/master/rules/network/zeek
- https://attack.mitre.org/techniques/T1573/001/
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