Security readout for executives and security teams
Plain-English summary
CVE-2021-26088 affects Fortinet FSSO authentication components. An unauthenticated nearby attacker could spoof login notification traffic and bypass an FSSO-based firewall policy, potentially reaching protected network resources. The issue is high severity, but the provided sources do not show confirmed active exploitation.
Executive priority
Treat as a priority for networks relying on Fortinet FSSO for access control. The business concern is unauthorized access through authentication-policy bypass, not broad internet-scale compromise based on current evidence.
Technical view
The vulnerability is improper authentication in FSSO Collector version 5.0.295 and below. Crafted UDP login notification packets may let an unauthenticated user bypass FSSO firewall policy. CVSS 3.1 is 7.1: adjacent network, low complexity, no privileges, no user interaction, changed scope, and low confidentiality, integrity, and availability impact.
Likely exposure
Exposure is likely limited to organizations using affected Fortinet FSSO Collector, FSSO Windows DC Agent, or FSSO Windows CA versions in firewall authentication policy flows.
Exploitation context
The source bundle does not identify public exploitation or CISA KEV listing. Risk depends on whether an attacker can send traffic on the relevant adjacent network path to FSSO authentication components.
Researcher notes
Evidence is sufficient for affected component, vulnerability class, and impact direction. The bundle does not provide a fixed version, exploit maturity, or detailed detection logic, so remediation should be anchored to Fortinet’s advisory.
Mitigation direction
- Inventory Fortinet FSSO Collector, Windows DC Agent, and Windows CA deployments and record exact versions.
- Follow Fortinet FG-IR-20-191 guidance for upgrades or vendor-approved mitigations.
- Restrict UDP login-notification traffic to trusted FSSO and firewall components where operationally possible.
- Review FSSO-dependent firewall policies for compensating controls and segmentation.
- Monitor vendor advisories for any updated remediation or exploitation guidance.
Validation and detection
- Confirm whether FSSO Collector or affected FSSO Windows components are deployed.
- Compare installed versions against 5.0.295 and below, including 5.0.294 and 5.0.295.
- Identify firewall policies that trust FSSO login notifications for access decisions.
- Review network paths that can reach FSSO UDP login-notification handling.
- Check logs for unusual FSSO login-notification patterns or unexpected policy bypass reports.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
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CVE-2021-26088 mapping review
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Open ATT&CK lookup- Severity
- High
- CVSS
- 7.1 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:L
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:L2.83.7Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
7.1HighVector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:L
Source materials
- CVE List V5 sourceCVE List V5
- https://fortiguard.com/advisory/FG-IR-20-191CVE reference · x_refsource_CONFIRM
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.