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CVE-2026-71933 – Missing Authorization / Configuration Tampering & DoS – DrayTek VigorSwitch Series

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Summary

CVE-2026-71933 is a missing-authorization vulnerability (CWE-862) affecting multiple DrayTek VigorSwitch models. The flaw resides in the switches’ syslog-related management functions, which fail to enforce proper authorization checks, allowing a remote, unauthenticated attacker to send crafted requests that modify device configuration, restart services, save the startup configuration, or clear logs. The issue was published on August 24, 2026 and rated CRITICAL (CVSS v3.1) / HIGH (CVSS v4.0), reflecting its network-exploitable, no-privilege-required nature and its potential to disrupt switch integrity and availability.

Technical details

  • Root cause: Multiple syslog-handling functions in VigorSwitch firmware lack the authorization checks needed to verify that a caller is a legitimate, authenticated administrator before executing privileged operations.
  • Trigger conditions: An attacker sends specially crafted requests to the exposed syslog functions on the switch’s management interface; no valid credentials or user interaction are required.
  • Attack vector: Network — exploitable remotely against any device where the management interface is reachable.
  • Impact: Unauthorized modification of device configuration, forced service restarts, forced saving of a startup configuration, and clearing of logs — enabling configuration tampering, loss of forensic/audit trail (log clearing), and denial of service through service restarts. The CVSS metrics indicate no confidentiality impact but high integrity and high availability impact.

Affected software

All below are DrayTek Corporation VigorSwitch models running firmware prior to the listed fixed version:

  • VigorSwitch G2540xs, P2540xs, FX2120 — versions before 3.9.10
  • VigorSwitch G2282x, P2282x — versions before 2.10.6
  • VigorSwitch Q2300x, PQ2300xb — versions before 2.10.7
  • VigorSwitch G2542x, P2542x, P2542xh — versions before 3.10.6
  • VigorSwitch PX2060, G1280, P1280, P1281x, G1282, P1282, G2121, P2121, PQ2121x, Q2121x, G2280x, P2280x, Q2200x, PQ2200xb, G2100, P2100, G2540x, P2540x — versions before 2.9.10

Severity

  • CVSS v3.1 Base Score: 9.1 (Critical)
    Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H
  • CVSS v4.0 Base Score: 8.8 (High)
    Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:H/SC:N/SI:N/SA:N

Mitigation and recommended actions

  • Immediate: Upgrade affected VigorSwitch devices to the fixed firmware version corresponding to your model:
    • G2540xs / P2540xs / FX2120 → 3.9.10 or later
    • G2282x / P2282x → 2.10.6 or later
    • Q2300x / PQ2300xb → 2.10.7 or later
    • G2542x / P2542x / P2542xh → 3.10.6 or later
    • All other listed models → 2.9.10 or later
  • If patching cannot be performed immediately:
    • Restrict access to the switch management interface to trusted internal networks only; do not expose it to the internet.
    • Place management interfaces behind a VPN or dedicated management VLAN with strict ACLs.
    • Monitor switch configuration, logs, and service uptime for unexpected changes, restarts, or log-clearing events that could indicate exploitation.
    • Review firewall/ACL rules to block unsolicited inbound traffic to switch management ports from untrusted sources.

References

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