Ransomware has become one of the most disruptive cyberthreats facing individuals and organizations today. A particularly vicious strain is Cerber, which has been active since 2016. Victims of Cerber are met with a ransom note demanding payment in Bitcoin to receive a decryption key. But is paying the ransom the only way to get files back? Or are there decryption tools that could do the job? This article will provide an overview of Cerber and the ongoing battle to crack its encryption.
How Cerber Encrypts Files
Cerber is a form of cryptographic ransomware, meaning it uses strong encryption algorithms to lock files. Early versions relied on RSA-2048 encryption, but later iterations utilize an even more robust AES-256 algorithm. This process works as follows:
1. Cerber is installed on a system, often when a user clicks on an infected email attachment or compromised website. It then contacts its command and control server to obtain the encryption key.
2. The malware recursively scans local drives and network shares to find files to encrypt. Targeted file types include documents, images, audio, video, archives, and databases.
3. Files are encrypted on a per-file basis using the public-private key pair. The private key to decrypt each file is stored on the attacker’s server.
4. Encrypted files are renamed with a new extension: .cerber, .cerber2, .cerber3 depending on the variant.
5. The ransom note is dropped demanding payment in Bitcoin to receive the decryption key. Amounts can range from $500-$1000 or more.
This process leverages asymmetric encryption where the public key encrypts and the private key decrypts. Without access to the unique private key, it is nearly impossible to restore encrypted files.
Challenges in Decrypting Cerber
Due to the strength of the encryption algorithms used, viable Cerber decryption tools remain elusive. There are several challenges security experts and malware analysts face in breaking Cerber’s encryption:
– Missing private key – The private keys to decrypt files reside solely on the attacker’s server. Without access to these keys, decryption cannot occur.
– Unique per-file encryption – Keys are generated on a per-file basis, not per-system. This means obtaining one key does not aid in decrypting other files.
– Payment validation – Paying the ransom provides the key, but attackers often build in payments validators to prevent keys from working if they do not see their payment.
– Evolving algorithms – Cerber continually improves its encryption schemes with each new version. This requires constant effort to find new vulnerabilities.
– Well-implemented cryptography – Unlike some ransomware, Cerber appears to use cryptography correctly without significant flaws. Standard cryptanalysis techniques have not been effective.
– Dead man’s switch – Cerber’s infrastructure may have a dead man’s switch to delete keys if servers are tampered with. This adds risk for law enforcement disruptions.
For these reasons, free decryption tools for Cerber have not materialized. Even security companies with resources dedicated to ransomware decryption have not yet cracked Cerber. However, research efforts continue.
Attempts at Decryption
Despite the challenges, security researchers have made some attempts at finding weaknesses in Cerber’s encryption schemes. Most have not resulted in complete decryption ability, but provide direction for ongoing analysis.
– Flawed key generation – Some early Cerber variants had flaws in random number generation during key creation. This allowed prediction of some private keys. But this was fixed in later versions.
– Recovery of RSA private keys – When Cerber used RSA encryption, researchers found methods to recover the RSA private key on an infected host. But this does not work with AES encryption.
– Exploiting the downloader – Cerberdownloads its executable files via an insecure HTTP connection. Researchers tried man-in-the-middle attacks to grab encryption keys during download, with varying success.
– Reverse engineering malware samples – Analysts have reverse engineered malware samples to extract inner workings of encryption routines. This provides some insight but not enough to construct decryption tools.
– Disrupting command and control infrastructure – Law enforcement agencies have tried to takedown Cerber’s C2 servers to disrupt key retrieval. This has impeded attackers but also resulted in lost keys.
While a definitive decryption solution remains elusive, this research has yielded some important insights into Cerber’s operation. It provides a starting point should new vulnerabilities be discovered.
Payment and Data Recovery
With no free decryption tools currently available, victims of Cerber are faced with a difficult choice: pay the ransom or attempt data recovery. There are pros and cons to each approach:
– Paying the ransom provides the decryption key but financially rewards and enables cybercriminals. There is no guarantee files will be recovered if payment issues arise.
– Data recovery without the key can utilize file carving to restore some files. But this is imperfect, time-consuming, and often fails for database files or without file metadata.
– Waiting for a decryption tool requires patience and carries the risk that one may never materialize. In the meantime, files remain inaccessible.
– Restoring from backups is the best path to recovery but relies on having good backups in place before infection. Many victims do not.
Ideally, preventing ransomware attacks in the first place should be the priority for individuals and organizations. But recovery is sometimes a necessity if infection occurs.
Prevention of Cerber and Ransomware
As decryption tools remain scarce, following best practices to avoid ransomware attacks like Cerber is critical. Prevention should focus on:
– Keeping all software up-to-date to close security holes that ransomware exploits.
– Exercising caution around suspicious emails and links which distribute malware.
– Using ad blockers and avoiding high-risk websites when browsing.
– Installing antivirus software to detect and halt malware infections.
– Configuring firewalls to restrict inbound traffic and file-sharing.
– Enforcing the principle of least privilege for permissions and access.
– Developing and testing backup/recovery plans for critical data.
– Educating employees on ransomware risks and prevention tactics.
– Disabling tools like PowerShell and RDP if not explicitly needed.
– Considering cyber insurance to offset costs if an attack occurs.
Rigorous security hygiene and cyber resilience planning are the best defenses against ransomware attacks. For Cerber specifically, basic prevention measures can go a long way towards avoiding costly data recovery efforts down the road.
Conclusion
Cerber remains one of the most troublesome ransomware strains seen in the wild. Its use of robust encryption has stymied attempts to create free decryption tools thus far. Paying the ransom provides keys for recovery but financially rewards criminals and may fail. Restoring from backups is the most reliable path if available. For the time being, prevention through comprehensive cybersecurity practices is the key to avoiding Cerber and ransomware attacks altogether. But research efforts continue to seek vulnerabilities that could enable decryption in the future.