Security readout for executives and security teams
Plain-English summary
Fortinet FortiOS SSLVPN had a high-severity memory handling flaw before version 7.0.1. A remote attacker without credentials could send crafted SSLVPN requests and potentially run code on the device, although the published CVSS vector rates attack complexity as high.
Executive priority
Prioritize remediation for exposed Fortinet SSLVPN devices because this is a remote, unauthenticated code execution risk affecting a security perimeter service. No active exploitation evidence is provided in the bundle, but impact is high.
Technical view
CVE-2021-26109 is an integer overflow or wraparound in the SSLVPN memory allocator in FortiOS before 7.0.1. Crafted SSLVPN requests may corrupt heap control data and lead to potentially arbitrary code execution. CVSS is 8.1, with network attack vector, no privileges, no user interaction, and high impact to confidentiality, integrity, and availability.
Likely exposure
Organizations using Fortinet FortiOS with SSLVPN exposed and running versions before 7.0.1 are the relevant exposure group. The bundle does not identify other products or configurations.
Exploitation context
The source bundle does not show CISA KEV listing or active exploitation. The CVSS vector includes high attack complexity and proof-of-concept exploit maturity, so treat exposed SSLVPN appliances as important to validate and remediate.
Researcher notes
Focus validation on FortiOS SSLVPN instances before 7.0.1. The flaw is memory-corruption related, with possible heap control data corruption. Evidence provided does not include exploit details, affected subversions beyond before 7.0.1, or compensating controls.
Mitigation direction
- Upgrade affected FortiOS systems to version 7.0.1 or later.
- Check Fortinet advisory FG-IR-21-049 for current vendor guidance.
- Prioritize internet-facing SSLVPN appliances for remediation.
- Restrict SSLVPN exposure where operationally feasible until upgraded.
Validation and detection
- Inventory FortiOS versions on all Fortinet SSLVPN appliances.
- Confirm whether SSLVPN is enabled and externally reachable.
- Verify upgraded systems report FortiOS 7.0.1 or later.
- Review Fortinet advisory FG-IR-21-049 against local asset versions.
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
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ATT&CK lookup starting points
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Execution behavior lookup
The CVE wording references code or command execution, so execution technique review may help defensive triage. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2021-26109 mapping review
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Open ATT&CK lookup- Severity
- High
- CVSS
- 8.1 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H/E:P/RL:U/RC:C
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:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H/E:P/RL:U/RC:C2.25.9Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
8.1HighVector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H/E:P/RL:U/RC:C
Source materials
- CVE List V5 sourceCVE List V5
- https://fortiguard.com/advisory/FG-IR-21-049CVE 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.