CVE-2025-62839 in Hybrid Backup Sync
Summary
by MITRE • 10/29/2026
An use of hard-coded cryptographic key vulnerability has been reported to affect HBS 3 Hybrid Backup Sync and Hybrid Backup Sync. If exploited, the vulnerability could allow remote attackers to compromise the security of the system.
We have already fixed the vulnerability in the following version: HBS 3 Hybrid Backup Sync 26.4.0.521 and later Hybrid Backup Sync 26.4.0.521 and later Hybrid Backup Sync 26.4.1.563 and later
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Analysis
by VulDB Data Team • 10/29/2026
The reported vulnerability in Synology HBS 3 Hybrid Backup Sync represents a critical failure in cryptographic key management, specifically categorized under CWE-798: Use of Hard-coded Cryptographic Key. This flaw arises when sensitive encryption keys are embedded directly within the application source code or binary distribution rather than being generated dynamically during installation or derived from user-provided secrets. In modern security architectures, hard-coding keys is considered a severe anti-pattern because it eliminates the ability to rotate credentials in response to potential compromises and creates a single point of failure for all instances of the software that share the same embedded key material. The presence of such static keys allows any actor with access to the application binary or its associated libraries to extract the cryptographic secrets, thereby undermining the confidentiality guarantees intended by the encryption mechanisms employed by the backup solution.
From an operational perspective, this vulnerability poses a significant risk to data integrity and privacy for users relying on HBS 3 for hybrid cloud storage synchronization. If remote attackers successfully exploit this weakness, they can decrypt sensitive backup data that is transmitted between local devices and Synology Cloud or other supported target destinations. This compromise effectively neutralizes the encryption layer designed to protect user files from interception during transit or exposure at rest if keys are also stored insecurely on endpoints managed by the application. The ability of an adversary to derive valid decryption keys means that even encrypted backups can be read, modified, or exfiltrated without detection, leading to potential data breaches and loss of trust in the backup infrastructure. This aligns with ATT&CK technique T1557: Adversary-in-the-Middle, where attackers intercept and potentially alter communications between two parties who believe they are directly communicating with each other, as well as T1028: File Transfer via Remote Service if the stolen keys facilitate unauthorized access to backup repositories.
The remediation for this vulnerability has been implemented in specific software releases that enforce proper key generation practices or utilize secure hardware-backed storage mechanisms where applicable. Users must upgrade their Synology NAS operating system and HBS 3 application to version 26.4.0.521, Hybrid Backup Sync 26.4.0.521, or later versions such as 26.4.1.563. These updates likely replace the static key implementation with a dynamic key exchange protocol or ensure that keys are derived from unique per-device seeds rather than shared global constants. It is imperative for administrators to verify their current software version immediately and apply these patches through the Synology DSM update center or HBS 3 interface. Until this upgrade is completed, organizations should assume that any data synchronized using older versions of HBS 3 may be susceptible to decryption by adversaries who have obtained reverse-engineering capabilities against the application binaries.
To further mitigate risks associated with cryptographic key management in backup solutions, administrators should adopt a defense-in-depth strategy. This includes ensuring that all network traffic is secured via TLS where possible, even if internal encryption keys are compromised, as this adds an additional layer of authentication and integrity checking. Regular audits of third-party libraries used within the application can help identify other potential hard-coded secrets or outdated cryptographic algorithms. Furthermore, implementing strict access controls on NAS devices ensures that only authorized personnel can modify backup configurations, reducing the attack surface for local privilege escalation attacks that might precede exploitation of this vulnerability. Continuous monitoring and logging should be enabled to detect any anomalous decryption activities or unauthorized key usage patterns that could indicate an ongoing compromise attempt leveraging these static credentials.