Cerber Ransomware Variant C3RB3R Targets Synology NAS Devices via Two Recently Disclosed Vulnerabilities

Since October this year, 360 Anti-Ransomware teams have responded to multiple incidents involving encryption attacks on Synology NAS appliances. Analysis by 360 AI security experts identified the threat as C3RB3R, a variant of the long-standing Cerber ransomware family that has historically focused on NAS targets. Attackers leveraged two high-risk remote vulnerabilities disclosed only one month earlier, CVE-2026-13639 and CVE-2026-13684, in classic 1-day exploitation scenarios. After gaining access, the malware follows traditional ransomware behavior: it scans file systems while skipping 27 system directories and specific extensions, then encrypts files using ChaCha8 combined with RSA-2048 before appending the .L0CK3D extension and dropping ransom notes. Synology released patches for eight vulnerabilities, including the two exploited ones, across multiple DSM versions starting 18 September 2026. The report includes detailed encryption logic, a full list of 187 priority extensions, and a set of practical hardening recommendations for NAS administrators.

安全客October 30, 2026Translated from Chinese

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Since October this year, 360 Anti-Ransomware Service teams have received multiple assistance requests concerning ransomware attacks targeting Synology NAS devices. Using 360 AI Security Expert capabilities, analysts sampled and examined compromised systems, confirming that the current campaign is driven by C3RB3R, a variant of the established Cerber ransomware family that has long specialized in encrypting NAS storage.

The attack vector consists of two high-severity remote vulnerabilities disclosed in September 2026: CVE-2026-13639 and CVE-2026-13684. Because the flaws were made public only about a month before the observed incidents, many devices remain unpatched, creating a classic 1-day exploitation opportunity.

Attack Flow: Cerber Uses New Entry Points but Retains Classic Encryption Tactics

Although the initial access stage employs the two fresh 1-day vulnerabilities, once inside the victim device the malware performs the familiar ransomware sequence of scanning, encrypting, dropping a ransom note, and demanding payment.

1. System Scanning

C3RB3R skips 27 directories to avoid encrypting critical system files that could crash the device and interrupt encryption. The excluded paths are:

/boot, /run, /proc, /sys, /dev, /etc, /config, /sbin, /bin, /lib, /lib32, /lib64, /usr/sbin, /usr/bin, /usr/lib, /usr/lib32, /usr/lib64, /usr/include, /usr/local, /usr/share, /usr/src, /usr/syno, /var/packages, /var/lock, /var/run, /var/tmp, /tmp

The sample also avoids common executable and script extensions as well as already-encrypted files (.exe, .dll, .lnk, .sys, .msi, .bat, .mod, read-me3.txt, C3RB3R_LOG.txt, init-rsysd.lo, init-ld.lo, .L0CK3D).

2. File Encryption

Encryption is performed with the widely used combination of ChaCha8 (symmetric) and RSA-2048 (asymmetric). For each target file the malware generates a unique 256-bit key and 64-bit nonce, encrypts the content with ChaCha8, then uses its embedded RSA public key to protect the encryption metadata. The resulting ciphertext is appended to the original file, which is renamed with the .L0CK3D extension.

Files whose extensions appear in a built-in priority list of 187 types receive full-file encryption regardless of size. Other files are encrypted selectively according to their size: complete encryption for files under ~1 MB, header-only encryption for files between ~1 MB and ~5 MB, and segmented encryption for larger files.

3. Ransom Note

In every encrypted directory the malware drops a file named read-me3.txt containing payment instructions. The note references a six-character device identifier generated locally on the victim system.

Synology Releases Patches for Eight Vulnerabilities

Synology published updates addressing the exploited flaws on 18 September 2026. The following DSM versions contain the fixes:

DSM 7.4 – update to 7.4-90075 or later
DSM 7.3 – update to 7.3.2-86009-4 or later
DSM 7.2.2 – update to 7.2.2-72806-9 or later
DSM 7.2.1 – update to 7.2.1-69057-12 or later

The eight CVEs fixed in this advisory cover arbitrary file read/write, denial-of-service, and information-disclosure issues affecting both unauthenticated and authenticated remote attackers.

Security Recommendations

Monitor security advisories and apply NAS firmware updates immediately.
Avoid exposing management ports directly to the internet; use VPN or vendor-provided relay services instead.
Disable default administrator accounts, enforce strong passwords, and enable two-factor authentication and automatic IP blocking.
Activate shared-folder snapshots with tamper protection and verify snapshot creation regularly.
Maintain at least one offline, air-gapped backup of critical data.
Enable the device firewall, restrict management access to trusted IP addresses, and review logs for suspicious activity.
Remove unused shared links, packages, and services to reduce the attack surface.
Never pay the ransom.

IOC: MD5 a1375e0f82ae86df528876c049b5a23c

Cerber CVE-2026-13639 CVE-2026-13684 Synology DSM ChaCha8 RSA-2048

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