Sicarii Ransomware Contains Fatal Coding Flaw That Makes Decryption Impossible Even After Payment
A critical coding error in the Sicarii ransomware, possibly introduced through over-reliance on AI-assisted development tools, renders decryption impossible for both victims and the ransomware operators themselves, according to researchers at Halcyon's Ransomware Research Center.
The flaw means that paying the ransom will not result in data recovery. Halcyon is advising all Sicarii victims: "Don't pay a Sicarii ransom. You won't get anything useful back."
Encryption Keys Discarded During Attack
Technical analysis by Halcyon's malware analysts revealed that while the Sicarii binary includes a functional RSA implementation, it is used in a way that fundamentally undermines recoverability.
During execution, the malware generates a new RSA key pair locally, uses the newly generated key material to encrypt victim files, and then discards the private key. This per-execution key generation means encryption is not tied to a recoverable master key.
The result is permanent data loss. Neither the victim nor the Sicarii operators can reconstruct the required key material to decrypt impacted systems. Any decryptor provided by the attackers will be ineffective because the necessary private key no longer exists.
AI "Vibe Coding" May Be to Blame
Halcyon assesses with moderate confidence that the Sicarii developers may have used AI-assisted tooling during development, which could have contributed to this critical implementation error.
The finding adds to growing concerns about threat actors using AI to accelerate malware development without fully understanding the code being generated. In this case, the error has rendered the ransomware more destructive than intended — victims face permanent data loss with no path to recovery, even through ransom payment.
Emerged in December 2025
Sicarii emerged as a ransomware-as-a-service operation in December 2025, when it began advertising for affiliates on dark web forums. The operation follows the standard RaaS model where developers provide the ransomware infrastructure and affiliates conduct attacks in exchange for a percentage of ransom payments.
There is currently no reliable evidence that this defect can be corrected for systems already encrypted by the affected variant. Organizations that have already been hit by Sicarii should assume their data is unrecoverable through attacker-provided tools.
Recommendations
Organizations impacted by Sicarii ransomware should immediately shift from ransom negotiation to restoring operations through alternate recovery pathways such as backups. Affected systems should be isolated to contain impact, and forensic evidence should be preserved.
Halcyon recommends engaging experienced ransomware incident response specialists to support investigation, containment, and recovery planning.
For proactive defense, organizations should deploy dedicated anti-ransomware solutions that block execution of malicious binaries, detect ransomware runtime behavior and data exfiltration attempts, and prevent the network intrusion and lateral movement that enable ransomware propagation.
The incident underscores why security professionals advise against paying ransoms — there is never a guarantee of data recovery, and in the case of Sicarii, recovery is technically impossible regardless of payment.
