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FortiosOperating system · Fortinet

CVE-2021-24018

HIGH · 8.8 CVSS v3.1 Published 2021-08-04
Fix available
A fix is available. Upgrade to 6.2.10 / 6.4.7 or later.
See remediation →
93/100
Remediation priority · Urgent
No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
A buffer underwrite vulnerability in the firmware verification routine of FortiOS before 7.0.1 may allow an attacker located in the adjacent network to potentially execute arbitrary code via a specifically crafted firmware image.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

A buffer underwrite vulnerability in FortiOS firmware verification allows an attacker on the adjacent network to potentially execute arbitrary code by presenting a specially crafted malicious firmware image. The vulnerability occurs in the verification routine that processes firmware before installation.

MitigationUpgrade FortiOS to version 7.0.1 or later. If immediate patching is not possible, restrict network access to the management interface and implement strict firmware image signing verification controls.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
FortiosOperating system
Affected:< 6.2.10>= 6.4.0, < 6.4.7= 7.0.0

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Adjacent
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify FortiOS version
    Log into the FortiGate CLI and run the command: `get system status` or `show system version`. This displays the current firmware version installed on the device.
    Affected if The version displayed falls within < 6.2.10, >= 6.4.0 but < 6.4.7, or equals 7.0.0
  2. Verify management interface exposure
    Review network configuration to determine if the FortiOS management interface (HTTP/HTTPS/SSH on port 443/4433/22) is accessible from untrusted or adjacent networks. Check interface bindings with `show system interface` and policy configurations with `get firewall policy`.
    Affected if The management interface is reachable from an adjacent or untrusted network without restrictive ACLs
  3. Check firmware image signature verification
    In FortiOS CLI, run: `get system global | grep -i sign` or check for firmware signature verification settings under `system firmware`. Also review `execute firmware list` output for configured upgrade paths.
    Affected if Firmware signature verification is disabled or not enforced for firmware upgrades

A FortiOS device is affected if it runs version 6.2.10 or later but less than 6.4.7, or exactly version 7.0.0, and the management interface is accessible from an adjacent network where an attacker could present a specially crafted firmware image.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 6.2.10 / 6.4.7 or later
Fixed in 6.2.106.4.7
Interim mitigation

Upgrade FortiOS to version 7.0.1 or later. If immediate patching is not possible, restrict network access to the management interface and implement strict firmware image signing verification controls.

Recommended fix High confidence

Upgrade to FortiOS 6.2.10 or later (if on 6.2.x); 6.4.7 or later (if on 6.4.x); 7.0.1 or later (if on 7.0.0). Prefer latest stable 7.0.x release for longest support.

  1. 1. Identify the current FortiOS version by running 'get system status' or checking the FortiGate device GUI.
  2. 2. Based on the current version branch, upgrade to the minimum fixed version: if on 6.2.x upgrade to 6.2.10 or later; if on 6.4.x upgrade to 6.4.7 or later; if on 7.0.0 upgrade to 7.0.1 or later.
  3. 3. Download the appropriate firmware image from the Fortinet Customer Support portal (https://support.fortinet.com/).
  4. 4. Upload the firmware via FortiGate GUI: System > Firmware > Upload, or via CLI using 'execute firmware upgrade' command.
  5. 5. After upgrade, verify the new version is installed by running 'get system status' and confirm it shows version 6.2.10+, 6.4.7+, or 7.0.1+.
  6. 6. Test critical firewall policies and VPN connections to ensure functionality is intact.
Caveat Standard FortiOS upgrade considerations apply: review release notes for behavioral changes, backup configuration, and test policies/VPNs before production deployment.

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Fortios Scoped from the published advisory
  • Consultation3.0 h
  • Implementation4.0 h
  • Testing3.0 h
  • Review / QA2.0 h
12.0 hours of engineering $2,130
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-24018 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data