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FortiosOperating system · Fortinet

CVE-2020-12819

HIGH · 7.5 CVSS v3.1 Published 2024-12-19
Fix available
A fix is available. Upgrade to 5.6.13 / 6.0.11 or later.
See remediation →
81/100
Remediation priority · High
Remotely reachable 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 heap-based buffer overflow vulnerability in the processing of Link Control Protocol messages in FortiGate versions 5.6.12, 6.0.10, 6.2.4 and 6.4.1 and earlier may allow a remote attacker with valid SSL VPN credentials to crash the SSL VPN daemon by sending a large LCP packet, when tunnel mode is enabled. Arbitrary code execution may be theoretically possible, albeit practically very difficult to achieve in this context

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

Heap-based buffer overflow in FortiGate SSL VPN's processing of Link Control Protocol (LCP) messages. A remote attacker with valid SSL VPN credentials can send a large LCP packet in tunnel mode to overflow a heap buffer, causing denial of service by crashing the SSL VPN daemon, with theoretical but difficult potential for arbitrary code execution.

MitigationUpgrade FortiGate to versions 6.0.11+, 6.2.5+, 6.4.2+ or later. Until patched, limit SSL VPN access to trusted users only and monitor for service disruptions.

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:< 5.6.13>= 6.0.0, < 6.0.11>= 6.2.0, < 6.2.5>= 6.4.0, < 6.4.2

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
Network
Complexity
High
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:H/PR:L/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 firmware version
    Run 'get system status' or 'fortios -v' via CLI to retrieve the installed FortiOS version number
    Affected if The version falls within any of these ranges: < 5.6.13, >= 6.0.0 and < 6.0.11, >= 6.2.0 and < 6.2.5, or >= 6.4.0 and < 6.4.2
  2. Verify SSL VPN is enabled
    Run 'show vpn ssl settings' or check via web UI under VPN > SSL-VPN Settings to confirm SSL VPN is configured and enabled
    Affected if SSL VPN is enabled and the FortiOS version is in an affected range listed above
  3. Check SSL VPN mode configuration
    Run 'get vpn ssl settings' and look for 'tunnel-mode' or 'ssl.vpn.tunnel.mode' - LCP processing in tunnel mode is required for exploitation
    Affected if SSL VPN is operating in tunnel mode and the FortiOS version is vulnerable
  4. Review SSL VPN user accounts
    Run 'show vpn ssl user' to list configured SSL VPN users - exploitation requires valid SSL VPN credentials
    Affected if Any SSL VPN users exist and the device is running a vulnerable FortiOS version with SSL VPN enabled in tunnel mode
  5. Monitor for SSL VPN daemon crashes
    Check system logs with 'execute log filter category 22' (event logs) or review '/var/log/messages' for 'sslvpn' daemon restart events indicating potential exploitation attempts
    Affected if Repeated SSL VPN daemon crashes or restarts occur on a vulnerable version

A user is affected if the FortiOS version is in a vulnerable range AND SSL VPN is enabled in tunnel mode with at least one configured user account.

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 5.6.13 / 6.0.11 / 6.2.5 or later
Fixed in 5.6.136.0.116.2.5
Interim mitigation

Upgrade FortiGate to versions 6.0.11+, 6.2.5+, 6.4.2+ or later. Until patched, limit SSL VPN access to trusted users only and monitor for service disruptions.

Recommended fix High confidence

Upgrade to FortiOS 5.6.13 / 6.0.11 / 6.2.5 / 6.4.2 or later (choose the appropriate version for your hardware model and current branch)

  1. 1. Identify current FortiOS version using 'get system status' command in FortiGate CLI
  2. 2. Download the appropriate fixed firmware from Fortinet Support Portal based on your current version branch
  3. 3. Review Fortinet release notes for your target version for any known issues
  4. 4. Backup current FortiGate configuration using 'execute backup config flash' or 'execute backup config tftp'
  5. 5. Upload the new firmware via FortiGate Web UI (System > Firmware) or CLI ('execute restore image tftp <filename> <tftp-server>')
  6. 6. Confirm the firmware upgrade was successful with 'get system status'
  7. 7. Verify SSL VPN functionality is operational after upgrade
  8. 8. If running in HA cluster, follow Fortinet's recommended upgrade procedure for HA environments
Caveat Review FortiOS release notes - major version upgrades (e.g., 6.0 to 6.2) may introduce configuration changes and feature differences; always test in non-production environment first

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

Fix this in Fortios Scoped from the published advisory
  • Consultation6.0 h
  • Implementation4.0 h
  • Testing8.0 h
  • Review / QA4.0 h
22.0 hours of engineering $3,840
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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-2020-12819 in production — separate from our analysis above.

No notes yet

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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