How severe is CVE-2021-26088?

CVE-2021-26088 has a CVSS 3.x base score of 7.1, rated high severity. It is exploitable over an adjacent network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is low, integrity low, and availability low.

Is CVE-2021-26088 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (60th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-26088?

CVE-2021-26088 affects Fortinet Fortinet Single Sign-on. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-26088?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2021-26088 published?

CVE-2021-26088 was published on 2021-07-12 and last updated on 2026-06-17.

CVE-2021-26088

CVE-2021-26088 is a high-severity vulnerability in Fortinet Fortinet Single Sign-on with a CVSS 3.x base score of 7.1. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-287.

Key facts

Severity: High (CVSS 3.x base score 7.1)
CVSS v2: 5.8
EPSS exploit prediction: 1% (60th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-287
Affected product: Fortinet Fortinet Single Sign-on
Published: 2021-07-12
Last modified: 2026-06-17

Description

An improper authentication vulnerability in FSSO Collector version 5.0.295 and below may allow an unauthenticated user to bypass a FSSO firewall policy and access the protected network via sending specifically crafted UDP login notification packets.

Frequently asked questions

What is CVE-2021-26088?: An improper authentication vulnerability in FSSO Collector version 5.0.295 and below may allow an unauthenticated user to bypass a FSSO firewall policy and access the protected network via sending specifically crafted UDP login notification packets.
How severe is CVE-2021-26088?: CVE-2021-26088 has a CVSS 3.x base score of 7.1, rated high severity. It is exploitable over an adjacent network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is low, integrity low, and availability low.
Is CVE-2021-26088 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (60th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-26088?: CVE-2021-26088 affects Fortinet Fortinet Single Sign-on. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-26088?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2021-26088 published?: CVE-2021-26088 was published on 2021-07-12 and last updated on 2026-06-17.

References

https://fortiguard.com/advisory/FG-IR-20-191

Affected products (1)

cpe:2.3:a:fortinet:fortinet_single_sign-on:*:*:*:*:*:*:*:*

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