Reverse Encryption
Reverse Encryption [T1556.005]
Information
Name: Reversible Encryption
ID: T1556.005
Technique: T1556
Introduction
Reverse Encryption (T1556.005) is a sub-technique within the MITRE ATT&CK framework categorized under the Credential Access tactic. Attackers utilize reverse encryption by extracting encrypted credentials from compromised systems and decrypting them externally, thereby gaining access to sensitive information and resources. Unlike direct credential theft, reverse encryption involves obtaining encrypted data such as password hashes or encrypted tokens and then employing specialized cracking tools or services to reverse the encryption process offline.
Deep Dive Into Technique
Reverse encryption typically involves a two-step process:
Credential Extraction:
Attackers first gain initial access to a victim's system or network.
They identify and extract encrypted credentials such as password hashes (NTLM hashes, SHA hashes, bcrypt hashes), encrypted Kerberos tickets, or application-specific encrypted tokens.
Common extraction methods include:
Memory dumps (e.g., using tools like Mimikatz or ProcDump).
Credential storage files (e.g., Windows SAM database, LSASS memory dumps).
Network interception of encrypted credentials (e.g., Kerberos tickets from network traffic).
Offline Decryption (Reverse Encryption):
After extracting encrypted credentials, attackers transfer them to external systems under their control.
They use specialized cracking tools or services to reverse encryption and recover plaintext credentials. Common tools and methods include:
Password-cracking tools such as Hashcat, John the Ripper, Cain and Abel.
Rainbow tables or GPU-based brute-force attacks.
Cloud-based cracking services that leverage distributed computing resources to accelerate the cracking process.
Depending on encryption strength, attackers may employ dictionary attacks, brute-force attacks, hybrid attacks, or rule-based attacks to successfully recover plaintext credentials.
When this Technique is Usually Used
Attackers commonly employ reverse encryption in several attack scenarios and stages, including:
Initial Access Stage:
After gaining initial foothold, attackers extract encrypted credentials to escalate privileges or move laterally within the network.
Privilege Escalation and Lateral Movement:
Attackers leverage cracked credentials to escalate privileges or pivot to other systems within the target environment.
Persistence and Long-term Access:
Attackers periodically extract encrypted credentials to maintain persistent access to compromised systems, even if initial entry points are discovered and closed.
Credential Harvesting Campaigns:
Large-scale attacks targeting organizations to harvest encrypted credentials, decrypt them offline, and sell or reuse them in future campaigns.
How this Technique is Usually Detected
Detection of reverse encryption techniques involves monitoring and analyzing activities related to credential extraction and exfiltration:
Endpoint Detection and Response (EDR) Tools:
Detect unusual processes or memory dumps (e.g., LSASS memory dumps, SAM database access).
Identify suspicious tools (e.g., Mimikatz, ProcDump, LaZagne) executing on endpoints.
Network Monitoring and Intrusion Detection Systems (IDS):
Monitor network traffic for unusual data exfiltration patterns, especially encrypted credential dumps being transferred outside the network.
Detect anomalous Kerberos ticket requests or abnormal communication patterns indicative of credential extraction.
Log Analysis and Security Information and Event Management (SIEM):
Analyze Windows Event Logs for suspicious authentication attempts, password hash extraction events, or suspicious access to credential storage files.
Track audit logs for unauthorized access attempts or abnormal file access patterns.
Indicators of Compromise (IoCs):
Presence of known credential extraction tools (e.g., Mimikatz binaries, ProcDump executables).
Unusual file creation or modification events (e.g., memory dump files, SAM database copies).
Suspicious outbound network connections to unknown or malicious IP addresses or domains.
Detection of known password-cracking tool signatures or commands within the environment.
Why it is Important to Detect This Technique
Early detection of reverse encryption is critical due to the severe impacts it can have on organizations:
Credential Compromise and Unauthorized Access:
Attackers who successfully reverse encrypted credentials gain unauthorized access, escalating privileges and compromising sensitive systems or data.
Lateral Movement and Privilege Escalation:
Recovered credentials enable attackers to move laterally within the network, escalating privileges and potentially compromising multiple systems.
Data Breaches and Information Leakage:
Access to sensitive credentials can lead to large-scale data breaches, leakage of sensitive information, or intellectual property theft.
Operational Disruption and Financial Loss:
Credential compromise can disrupt business operations, resulting in operational downtime, remediation costs, regulatory fines, and reputational damage.
Persistent Threats:
Attackers maintaining persistent access through compromised credentials can continuously exfiltrate data, conduct espionage, or sabotage operations.
Examples
Real-world examples of reverse encryption attacks include:
Credential Dumping with Mimikatz:
Attackers use Mimikatz to dump LSASS memory, extracting encrypted NTLM hashes and Kerberos tickets.
Extracted encrypted credentials are transferred offline to attacker-controlled infrastructure, where Hashcat or John the Ripper are used to reverse encryption and retrieve plaintext passwords.
Impact: Attackers gain privileged access to internal systems, leading to lateral movement, data exfiltration, and potential ransomware deployment.
Kerberoasting Attacks:
Attackers request service tickets from Kerberos-enabled Active Directory environments, extracting encrypted Kerberos tickets.
Extracted tickets are cracked offline using tools like Hashcat, recovering plaintext service account passwords.
Impact: Attackers gain access to privileged service accounts, enabling further lateral movement and privilege escalation within the network.
Password Hash Extraction from Windows SAM Database:
Attackers extract the encrypted password hashes stored in the Windows Security Account Manager (SAM) database.
Offline cracking is performed using rainbow tables or GPU-accelerated cracking tools.
Impact: Attackers obtain user and administrator credentials, enabling persistent access, lateral movement, or sensitive data theft.
Cloud-based Credential Cracking Services:
Attackers extract encrypted credentials and upload them to cloud-based password-cracking services, utilizing distributed computing power to rapidly reverse encryption.
Impact: Rapid credential compromise, enabling attackers to quickly escalate privileges, move laterally, and compromise sensitive resources before detection.
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