VECT Ransomware Exposed: How a Fatal Encryption Flaw Turns Ransomware into a Permanent Wiper

Overview

In late 2025, the VECT ransomware-as-a-service (RaaS) operation emerged on Russian-language cybercrime forums, quickly gaining notoriety after a partnership with the supply-chain attack group TeamPCP. However, a deep technical analysis by Check Point Research revealed that VECT 2.0 suffers from a critical implementation flaw that makes it effectively a wiper for any file larger than 128 KB. This tutorial explains the inner workings of the encryption engine, the specific nonce-handling bug, and why it renders recovery impossible—even for the attackers themselves. By the end, you'll understand the vulnerability, how to detect it, and the broader implications for ransomware analysis.

Prerequisites

Required Knowledge

• Basic understanding of symmetric encryption (ChaCha20, nonces, AEAD)
• Familiarity with ransomware file structures and ransom notes
• Ability to read basic pseudocode or C-like code
• Concept of RaaS and affiliate models

Tools & Environment

• Sample VECT encrypted file (e.g., from a public sandbox)
• Hex editor (e.g., HxD, 010 Editor)
• Programming language with libsodium bindings (Python with PyNaCl is recommended)
• Disassembler (optional: IDA Pro, Ghidra) for deep verification

Step-by-Step Analysis of the VECT Encryption Flaw

1. Understanding the Encryption Engine

VECT uses raw ChaCha20-IETF (RFC 8439) with no authentication. This is not the ChaCha20-Poly1305 AEAD commonly misattributed in public reports. The encryption is based on libsodium and identical across Windows, Linux, and ESXi variants—confirming a single codebase.

Key points:

• Four 32-byte secret keys are derived from a master secret using BLAKE2b.
• A 12-byte nonce space is used (standard for IETF variant).
• Only 8 bytes of the nonce are randomized per file; the rest are fixed or derived.

The critical design is the four-chunk approach: for files ≤128 KB, the entire file is encrypted as one chunk; for larger files, the first 128 KB, the last 128 KB, and (for very large files) two additional chunks at 75% and 50% boundaries are encrypted. The rest of the file remains untouched but the metadata is altered.

2. Identify the Nonce Flaw

For each file, VECT generates a 12-byte nonce. The first 8 bytes are random (file-level unique), and the last 4 bytes are a chunk counter (0,1,2,3). The bug: When encrypting a file larger than 128 KB, the same random prefix is reused for all chunks. Worse, the chunk counter is incremented only in the lower 4 bytes, but due to an off-by-one error in the nonce generation code, the counter for chunks 1,2,3 is never written to the file header. It is stored as zero. As a result, when decrypting, the decryption routine uses the same nonce (random prefix + 0) for every chunk. The four chunks of the file are encrypted with identical nonces, meaning the keystream is reused. This breaks ChaCha20's semantic security.

// Simplified nonce generation
nonce = random_8_bytes || chunk_id (as 4-byte LE)
// Bug: chunk_id is computed but never copied to the file header
// Decryption uses nonce from header = random_8_bytes || {0,0,0,0}
// So chunk 0,1,2,3 all get the same nonce

3. Impact Analysis: From Ransomware to Wiper

Because the nonce is reused across chunks, an attacker who knows one chunk's plaintext can derive the keystream and decrypt the others. But the real implication is permanent data destruction: even the attacker cannot recover the original file because the encrypted chunks are XORed with the same keystream. This creates multiple potential collisions and makes the decryption key ambiguous. Moreover, the nonce reuse breaks the encryption entirely—recovery requires brute-forcing the key, which is infeasible.

For any file >128 KB, including VM disks, databases, documents, and backups, VECT essentially acts as a wiper. The threshold is extremely low, so virtually all meaningful files suffer this fate. Check Point confirmed this across all publicly available VECT versions.

4. Practical Verification (Python Example)

You can verify the nonce reuse by extracting the file header (first 104 bytes) from an infected file. The nonce is stored at offset 8 (8 bytes random + 4 bytes chunk counter). Compare the nonce for the first chunk with the reconstructed nonce for chunk 2. If they are identical, you've confirmed the flaw.

import struct

# Open an encrypted file (example)
with open('encrypted_sample.bin', 'rb') as f:
    header = f.read(104)
    # VECT header structure: 8 bytes magic, 8 bytes random, 4 bytes chunk counter, ...
    random_prefix = header[8:16]
    chunk_counter = struct.unpack('