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CVE-2026-71922 – Pre-Auth Denial of Service (Null Pointer Dereference) – DrayTek VigorSwitch Series

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Summary

CVE-2026-71922 is a pre-authentication NULL pointer dereference vulnerability (CWE-476) affecting the setget.cgi interface on multiple DrayTek VigorSwitch models. The flaw is triggered when a required pass field is missing from a request, causing the switch’s management service to crash. The vulnerability carries a CVSS v4.0 base score of 8.7 (High) and can be exploited remotely over the network with no authentication or user interaction, resulting in a denial-of-service condition.

Technical details

  • Root cause: The setget.cgi CGI handler on affected VigorSwitch firmware fails to validate the presence of the pass field before dereferencing it, leading to a NULL pointer dereference.
  • Trigger conditions: An attacker sends a specially crafted HTTP request to the setget.cgi endpoint that omits the expected pass parameter.
  • Attack vector: Network-based, pre-authentication — no credentials, privileges, or user interaction are required (AV:N/AC:L/PR:N/UI:N).
  • Impact: Causes the affected switch management service to crash, resulting in denial of service (availability impact only; no confidentiality or integrity impact per the CVSS vector). Repeated exploitation could be used to persistently disrupt switch management/administration availability.
  • Credit: Discovered by Jincheng Wang and Le Yu (Nanjing University) and Xiapu Luo (Hong Kong Polytechnic University).

Affected software

Multiple DrayTek VigorSwitch models, prior to the following fixed firmware versions:

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

Severity

  • CVSS v4.0: 8.7 (High) — CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
  • CVSS v3.1: 7.5 (High) — CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Mitigation and recommended actions

  • Immediate: Upgrade affected VigorSwitch models to the fixed firmware versions listed above (3.9.10, 2.10.6, 2.10.7, 3.10.6, or 2.9.10, depending on model), as published in DrayTek’s security advisory.
  • If patching cannot be performed immediately:
    • Restrict access to the switch management interface (including setget.cgi) to trusted internal networks only; do not expose switch management interfaces directly to the internet.
    • Use firewall/ACL rules or a management VLAN to limit which hosts can reach the switch’s web management CGI endpoints.
    • Monitor for repeated crashes or unavailability of the switch management service, which may indicate exploitation attempts.

References

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