NCSC Flags Eight Critical FortiOS Flaws
NCSC-NL advisory details eight FortiOS vulnerabilities, including a 9.8 CVSS auth bypass, enabling full admin takeover or traffic interception.
Sourceadvisories.ncsc.nl — open the original
What to check
- Applies to
- The 8 CVEs named below. Whether you run an affected version is not assessed: check the versions the source lists.
- Exploitation
- No exploitation in the wild and no public exploit is recorded for the CVEs named.
The Netherlands' NCSC has published advisory NCSC-2026-0489 covering eight vulnerabilities patched by Fortinet across FortiOS and related products. The flaws span a range of weaknesses: improper certificate validation in SSLVPN (allowing traffic interception), privilege escalation via an invalid token in the admin interface, unauthenticated manipulation of OSPF routing information, faulty iBGP data handling causing unexpected routing behaviour, SSH authentication bypass using manipulated credentials, a memory-corruption issue allowing code execution by an attacker with existing privileges, a WAD proxy/ZTNA denial-of-service, and a High Availability FGSP issue that can grant full administrative control without any account under certain configurations.
Eight CVEs are listed with CVSS v3 scores ranging from 6.6 up to 9.8 (CVE-2026-126259) and 9.6 (CVE-2026-126254), both rated critical in severity, alongside a 9.3 (CVE-2026-126253) and 8.1 (CVE-2026-121528). The advisory does not indicate active exploitation in the wild; it is a standard patch notification summarizing Fortinet's own FG-IR PSIRT bulletins (FG-IR-26-193, 195, 267, 268, 269, 270, 272, 273).
Defenders running FortiOS should prioritize patching per the linked Fortinet PSIRT advisories, with particular urgency for the HA FGSP unauthenticated admin takeover and the 9.8/9.6-rated issues. Review SSLVPN certificate validation settings, admin interface token handling, and HA FGSP configuration exposure as immediate mitigations while patches are rolled out.
Mentioned in this report
Source reporting: https://advisories.ncsc.nl/2026/ncsc-2026-0489.html
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