VECT: Ransomware That Can’t Decrypt

What Happened

VECT is a type of ransomware that locks files on Windows computers, but it is built so poorly that even the attackers cannot reliably unlock the files after a ransom is paid. The malware renames files before it actually finishes locking them, and it loses the digital "keys" needed to unlock larger files. Because of these bugs, victims might end up with permanently damaged files even if they obtain the decryption tool. Organizations should focus on stopping this ransomware before it runs and maintaining offline backups, as relying on the attacker's decryption tool is not a viable recovery strategy.

Key Takeaways

• VECT ransomware contains severe implementation flaws that prevent reliable file decryption, rendering the attacker's own decryptor ineffective.
• The malware renames files with a .vect extension before encrypting them, meaning the presence of the extension does not guarantee the file was successfully encrypted.
• For files larger than 128 KB, VECT uses four different nonces but only saves the final one in a 12-byte trailer, leading to unrecoverable data.
• A buffer-size mismatch and the use of process-global buffers across concurrent threads cause race conditions, resulting in inconsistent or damaged file states.

Affected Systems

• Windows (64-bit)

Attack Chain

VECT ransomware targets Windows systems by walking accessible paths and excluding specific system directories and executable file types. Upon targeting a file, it first appends the .vect extension and renames the file before initiating encryption. It utilizes ChaCha20-IETF for encryption, processing files concurrently using scanner and encryptor worker threads. Due to implementation flaws such as buffer-size mismatches and shared global state, files may be left in inconsistent states, partially encrypted, or permanently damaged without the necessary metadata for recovery.

Detection Availability

• YARA Rules: No
• Sigma Rules: No
• Snort/Suricata Rules: No
• KQL Queries: No
• Splunk SPL Queries: No
• EQL Queries: No
• Other Detection Logic: No

The article does not provide specific detection rules or queries.

Detection Engineering Assessment

EDR Visibility: High — EDRs can easily monitor mass file rename operations (appending .vect) and rapid file read/write sequences typical of ransomware behavior. Network Visibility: None — The article focuses entirely on local file encryption mechanics; no network C2 or exfiltration behavior is detailed. Detection Difficulty: Moderate — While mass file modifications are easy to detect, distinguishing VECT's specific buggy behavior from other ransomware requires deeper file analysis.

Required Log Sources

• File System Activity (e.g., Sysmon Event ID 11, 23)

Hunting Hypotheses

Control Gaps

• Relying on attacker-provided decryptors for recovery is ineffective due to malware bugs.

Key Behavioral Indicators

• Files renamed with a .vect extension
• 12-byte trailer appended to files containing a ChaCha20-IETF nonce

False Positive Assessment

• Low

Recommendations

Immediate Mitigation

• Verify against your organization's incident response runbook and team escalation paths before acting.
• If your EDR supports host isolation, consider isolating endpoints exhibiting mass file rename operations involving the .vect extension.

Infrastructure Hardening

• Evaluate whether critical data backups are stored offline or in immutable storage to prevent ransomware tampering and ensure recovery without relying on attacker tools.

User Protection

• Consider deploying anti-ransomware solutions that focus on pre-encryption execution prevention.

Security Awareness

• Educate stakeholders that paying the ransom for VECT may not result in data recovery due to inherent flaws in the malware's encryption logic.

MITRE ATT&CK Mapping

• T1486 - Data Encrypted for Impact
• T1485 - Data Destruction
• T1565.001 - Data Manipulation: Stored Data Manipulation