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CVE-2026-13684 – Unauthenticated Remote File Read/Write & DoS – Synology DSM before 7.4-90075 / 7.3.

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Summary

CVE-2026-13684 is a critical improper encoding/escaping vulnerability (CWE-116) affecting the SCGI component of Synology DiskStation Manager (DSM). The flaw allows a remote, unauthenticated attacker to read or write arbitrary files on the device and to trigger a denial-of-service condition. It carries a CVSS v3.1 base score of 9.8 (Critical) and was disclosed by Synology on September 18, 2026, alongside several other DSM issues in the same advisory.

Technical details

  • Root cause: improper encoding or escaping of output within DSM’s SCGI (Simple Common Gateway Interface) handling, allowing attacker-controlled input to be mishandled when passed through the SCGI interface.
  • Trigger conditions: no authentication or user interaction is required; the vulnerable SCGI endpoint is reachable over the network.
  • Attack vector: Network (AV:N), low attack complexity (AC:L), no privileges required (PR:N), no user interaction (UI:N).
  • Impact: full compromise of confidentiality, integrity, and availability — arbitrary file read and write, and the ability to crash or disrupt DSM services (denial-of-service).

Affected software

  • Synology DSM 7.4 — versions before 7.4-90075
  • Synology DSM 7.3.2 — versions before 7.3.2-86009-4
  • Synology DSM 7.2.2 — versions before 7.2.2-72806-9
  • Synology DSM 7.2.1 — versions before 7.2.1-69057-12
  • Synology DSM versions earlier than 7.2.1

Severity

  • CVSS v3.1 Base Score: 9.8 (Critical)
  • Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Mitigation and recommended actions

  • Immediate: Update DSM to the fixed versions published by Synology — 7.4-90075 or later, 7.3.2-86009-4 or later, 7.2.2-72806-9 or later, or 7.2.1-69057-12 or later, depending on the currently installed release track.
  • If immediate patching is not possible, restrict network access to the DSM management interface (e.g., limit exposure to the internet, place behind a VPN or firewall, and disable unnecessary remote access services) until the update can be applied.
  • Review DSM devices exposed to the internet and prioritize patching for internet-facing units given the unauthenticated, network-exploitable nature of this vulnerability.

References

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