Blue Coat Alert Details
Alert ID: BLUECOAT-ENCRYPTED-1573-7842 Alert Time: 2024-02-29 09:30:15 EST Severity: HIGH (85/100) Source: Blue Coat ProxySG (Symantec Web Security Service) Rule: “Anomalous TLS Traffic – Custom Cipher Suite Detected” MITRE ATT&CK: T1573.001 – Encrypted Channel: Symmetric Cryptography
Alert Details:
Detection: TLS traffic using non-standard cipher suite to suspicious destination
User: rpatel@company.com (Raj Patel, Engineer) Source IP: 192.168.45.78 (Internal) Destination: 185.143.221[.]89:443 Time: 09:15-09:30 EST
TLS Handshake Details:
Protocol: TLS 1.2
Cipher Suite: TLS_RSA_WITH_AES_256_CBC_SHA256 (0x3c)
Note: This cipher suite is legitimate but rarely used (0.1% of traffic)
Server Certificate: Self-signed, CN=”*.cdn-updates.com”
Client Random: 4f8b3a1c7d2e5f9a6b3c8d1e4f7a2b9c (consistent across sessions)
Traffic Pattern:
09:15:22 – TLS handshake (2.1 KB)
09:15:25 – Encrypted data transfer (4.3 KB)
09:20:22 – TLS handshake (2.1 KB)
09:20:25 – Encrypted data transfer (4.3 KB)
(repeating every 5 minutes, 4 sessions total)
Detection Logic:
Destination IP known for malicious activity
Self-signed certificate for “update” domain (suspicious)
Cipher suite usage deviates from normal traffic patterns
Consistent session sizes (2.1 KB handshake, 4.3 KB data)
Pattern matches encrypted C2 beaconing
SOC Investigation Process
Step
Action
Tools Used
Findings
1. Alert Validation
Verify Blue Coat alert
Blue Coat ProxySG Console
Confirmed anomalous TLS traffic to malicious IP
2. Process Investigation
Identify process on endpoint
CrowdStrike Falcon
svchost.exe with injected Cobalt Strike beacon
3. Traffic Analysis
Decrypt traffic (with permission)
Wireshark, Private Key
Traffic contained encrypted C2 commands
4. Immediate Action
Isolate host
CrowdStrike
ENG-WS-045 quarantined
5. C2 Blocking
Block destination IP
Palo Alto, Blue Coat
IP 185.143.221[.]89 blocked
6. Malware Removal
Clean infected host
CrowdStrike Live Response
Cobalt Strike beacon removed
Jira Incident Report
Ticket: SOC-2024-146 Summary: T1573 – Encrypted C2 Channel Using Custom TLS Cipher Suite Status: RESOLVED Resolution: MALICIOUS – C2 Blocked Priority: P2 – MEDIUM Labels: T1573, encrypted-channel, tls, cobalt-strike, blue-coat Components: Network-Security, Endpoint-Security
INCIDENT ANALYSIS REPORT
1. Initial Context:
Detection Source: Blue Coat ProxySG.
Alert: “Anomalous TLS Traffic – Custom Cipher Suite Detected”.
User: rpatel@company.com (Engineering Department).
Host: ENG-WS-045.
Destination: 185.143.221[.]89:443.
Time: 2024-02-29 09:30 EST.
Technique: MITRE ATT&CK T1573.001 – Encrypted Channel: Symmetric Cryptography.
2. Technical Analysis:
Attack Chain:
08:30 – rpatel account compromised via phishing
08:45 – Attacker logs into ENG-WS-045 via RDP
08:50 – Cobalt Strike beacon deployed
09:00 – First beacon to C2
09:00-09:30 – 4 beacon sessions with encrypted traffic
09:30 – Blue Coat detects
TLS Analysis:
Cipher Suite: TLS_RSA_WITH_AES_256_CBC_SHA256 (0x3c)
Usage: <0.1% of normal traffic (highly anomalous)
Certificate: Self-signed, CN=”*.cdn-updates.com”
Handshake Size: Exactly 2.1 KB (consistent)
Data Size: Exactly 4.3 KB (consistent)
Malware Analysis:
Type: Cobalt Strike beacon
Process: Injected into svchost.exe
Encryption: AES-256-CBC with custom key exchange
Beacon Interval: 5 minutes
Decrypted Traffic (with permission):
09:15 – C2 command: “sleep 300” (already set)
09:20 – C2 command: “getuid” (whoami)
09:25 – C2 command: “ls C:\Users”
09:30 – C2 command: “exit” (beacon terminated)
3. Investigation Findings:
Timeline:
08:30 – Account compromised
08:45 – Attacker logs in
08:50 – Beacon deployed
09:00-09:30 – C2 communication
09:30 – Blue Coat alert
09:32 – SOC investigates
09:33 – Host isolated
09:34 – C2 blocked
Indicators of Compromise (IoCs):
Network:
– C2 IP: 185.143.221[.]89:443
– TLS cipher: 0x3c (TLS_RSA_WITH_AES_256_CBC_SHA256)
– Certificate CN: *.cdn-updates.com
Host:
– svchost.exe (injected)
– Cobalt Strike beacon (SHA256: a1b2c3d4…)
Account:
– rpatel (compromised)
4. Containment Actions:
Immediate Actions:
Isolated ENG-WS-045 via CrowdStrike.
Blocked C2 IP at firewall and proxy.
Terminated beacon process.
Disabled rpatel account.
Reset password.
Host Remediation:
Full scan, removed Cobalt Strike.
Reimaged as precaution.
User Remediation:
MFA enforced.
5. Root Cause Analysis:
Primary Cause: User account compromised, leading to malware deployment.
Contributing Factors:
No MFA on account.
RDP allowed from internet.
Encrypted channel evaded basic detection.
6. Business Impact:
Operational Impact: Engineering host offline for 2 hours.
Data Exposure: None (reconnaissance only).
7. Remediation & Prevention:
Completed Actions:
C2 blocked.
Malware removed.
Account secured.
Technical Controls Enhanced:
Enforced MFA for all users.
Moved RDP behind VPN only.
Enhanced TLS fingerprinting and anomaly detection.
8. Conclusion:
An attacker deployed a Cobalt Strike beacon that used TLS with a rare cipher suite to evade detection. Blue Coat identified the anomalous TLS traffic and enabled rapid containment before significant data could be exfiltrated.
Closure Rationale: C2 blocked; malware removed; account secured.
Analyst: [Your Name], SOC Analyst Date: 2024-02-29 10:30 EST