Ransomware Recovery Requires More Than Decrypting Files
Summary
A ransomware guide explains how data theft, credential compromise, and backup damage can outlast encryption, and covers recovery opportunities, evidence preservation, incident response, and resilient backup preparation.
Key points
- Ransomware incidents can combine encryption, data theft, credential compromise, operational disruption, and interference with backups; restoring files alone does not establish that the environment is safe.
- The article describes partial encryption, implementation weaknesses, recovered keys, and surviving file structures as possible recovery avenues, while stressing that outcomes depend on the specific sample and file format.
- It warns that attacker-supplied decryptors should be treated as untrusted code and that a decryptor's apparent success does not establish that it is safe.
- Response guidance emphasizes containing active damage, preserving useful evidence when safe, investigating identity systems and possible data theft, and securing credentials and sessions from a clean environment.
- Recovery should use trusted sources and be validated; the article distinguishes decryption, backup restoration, forensic reconstruction, application-level recovery, and retrieving repository content.
- Preparation recommendations include restricting administrative access, monitoring critical systems, protecting independent offline or immutable backups, and testing full restoration against recovery objectives.
- The article reports the Malware INFO Research Team's finding of an information stealer in a STOP/DJVU decryptor it examined, while cautioning that this observation should not be generalized to every decryptor.
Article Details
- Topic
- Ransomware evolution, data-theft risks, recovery limitations, and incident preparation
MITRE ATT&CK
T1485 · Data DestructionThe article describes Onyx overwriting larger files, destroying data rather than encrypting it.T1486 · Data Encrypted for ImpactRansomware encrypts files to disrupt availability.T1490 · Inhibit System RecoveryAttackers may interfere with backup infrastructure to obstruct recovery.T1555.003 · Credentials from Web BrowsersAZORult and Vidar are described as stealing browser credentials; Vidar also collected browser cookies.
Threat Actors
Cl0pThe article associates CL0P with MOVEit data theft.ContiThe article associates Conti with attacks on Costa Rican government systems.DarkSideThe article associates DarkSide with the Colonial Pipeline ransomware incident.LockBitThe article describes the ransomware operation retaining data from victims who had paid and an investigation that obtained decryption keys.SamSamThe article identifies SamSam in connection with an attack that disrupted municipal operations in Atlanta.
Malware
AzoRultAZORult accompanying STOPLinux.EncoderLinux.Encoder variants Predictable key-generation behavior and implementation errors Bitdefender developed recovery methods for particular versions, including iterations examined around 2015–2016. (Bitdefender)OnyxThe legacy Onyx ransomware examined in 2022 was reported to overwrite larger files rather than preserve them as decryptable ciphertext.RansomWarriorRansomWarrior, 2018 Selection from 1,000 hardcoded keys, with identifying information available to the recovery process Check Point extracted the key material and produced a decryptor. (Check Point Research)STOP/DJVU4. STOP/DJVU: Encryption May Be Only One PayloadTorrentLockerESET documented that TorrentLocker encrypted the first 2 MB of files in its 2014 implementation, while later variants examined in its 2016 research reduced this to the first 1 MB.VanHelsingFor example, Check Point’s 2025 analysis of a VanHelsing sample described full encryption for smaller files and encryption of the first 30% for files at or above a specified large-file threshold.VidarVidar accompanying STOP/DJVUWannaCry2017 WannaCry and England’s NHS The National Audit Office found that at least 81 of 236 NHS trusts were affected. Some were infected; others experienced disruption after taking defensive action. Ransomware can interruptZorabIn 2020, Zorab masqueraded as a STOP/DJVU recovery tool but instead encrypted victims’ files again.
Vendors
Products
ESXiIt is not a universal decryptor for arbitrary ESXi ransomware incidents.Progress MOVEit Transfer2023 CL0P-associated MOVEit data theft Mandiant investigated exploitation of a MOVEit Transfer zero-day to steal data. This illustrates data-theft extortion, which does not require encrypting victims’ files. (Mandiant /
Tools
ESXiArgs-RecoverCISA’s ESXiArgs-Recover project illustrates recovery without breaking encryption.WanaKiwicould sometimes reconstruct the private key before the relevant memory disappeared or was overwritten. (WanaKiwi project)WannaKeyThe WannaCry tools WannaKey/WanaKiwi demonstrated that, under specific operating-system and process-memory conditions, useful RSA material could remain in memory.
Countries
AustraliaAustralia’s privacy regulator described a breach affecting approximately 9.7 million individuals, with personal information subsequently released on the dark web.Costa Rica2022 Conti and Costa Rica Attacks on government systems disrupted tax and customs operations and severely affected foreign trade. Ransomware can become a national service-delivery problem. (US Department of State,
Industries
Government2022 Conti and Costa Rica Attacks on government systems disrupted tax and customs operations and severely affected foreign trade. Ransomware can become a national service-delivery problem. (US Department of State,Healthcare2024 Change Healthcare UnitedHealth reported US$3.090 billion in cyberattack impacts for 2024. Separately, Change Healthcare notified HHS OCR on 31 July 2025 that approximately 192.7 million individuals had been