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FortiadcApplication · Fortinet

CVE-2021-42757

MEDIUM · 6.7 CVSS v3.1 Published 2021-12-08
Fix available
A fix is available. Upgrade to after 7.0.2 or later.
See remediation →
69/100
Remediation priority · Elevated
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 overflow [CWE-121] in the TFTP client library of FortiOS before 6.4.7 and FortiOS 7.0.0 through 7.0.2, may allow an authenticated local attacker to achieve arbitrary code execution via specially crafted command line arguments.

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

Buffer overflow (CWE-121) in the TFTP client library of FortiOS versions before 6.4.7 and 7.0.0-7.0.2 allows an authenticated local attacker to achieve arbitrary code execution via specially crafted command line arguments.

MitigationUpgrade FortiOS to version 6.4.7 or later, or version 7.0.3 or later. Since this requires authenticated local access, enforce least-privilege principles and monitor for suspicious TFTP client usage patterns.

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
FortiadcApplication
Affected:>= 5.0.0, <= 6.1.5>= 6.2.0, <= 6.2.2
FortianalyzerApplication
Affected:>= 6.0.0, <= 6.4.7>= 7.0.0, <= 7.0.2
FortimailApplication
Affected:>= 5.4.0, <= 6.2.7>= 6.4.0, <= 6.4.6>= 7.0.0, <= 7.0.2
FortimanagerApplication
Affected:>= 6.0.0, <= 6.4.7>= 7.0.0, <= 7.0.2
FortindrApplication
Affected:>= 1.1.0, <= 1.5.2
Fortios 6k7kApplication
Affected:<= 6.2.8= 6.4.2= 6.4.6
FortiportalApplication
Affected:>= 5.0.0, <= 6.0.10
FortiproxyApplication
Affected:>= 1.0.0, <= 2.0.7= 7.0.0= 7.0.1

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

CVSS:3.1/AV:L/AC:L/PR:H/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 the Fortinet product in use
    Determine which Fortinet product runs in your environment (Fortiadc, Fortianalyzer, Fortimail, Fortimanager, Fortindr, FortiOS 6k7k, Fortiproxy, or Fortiportal) by reviewing system information or asset inventory.
    Affected if The product is any of the eight listed Fortinet products.
  2. Determine the installed product version
    Use the product's CLI or web interface to retrieve the firmware version. For FortiOS, run 'get system status' or 'fwctrl -v' via CLI. For Fortiadc/Fortimail/Fortimanager, use 'get system status' or check the dashboard.
    Affected if The product version cannot be determined or is not visible.
  3. Compare your version against the affected ranges
    Match the installed version to the affected version list: Fortiadc (5.0.0-6.1.5, 6.2.0-6.2.2), Fortianalyzer (6.0.0-6.4.7, 7.0.0-7.0.2), Fortimail (5.4.0-6.2.7, 6.4.0-6.4.6, 7.0.0-7.0.2), Fortimanager (6.0.0-6.4.7, 7.0.0-7.0.2), Fortindr (1.1.0-1.5.2), FortiOS 6k7k (<=6.2.8, 6.4.2, 6.4.6), Fortiportal (5.0.0-6.0.10), Fortiproxy (1.0.0-2.0.7, 7.0.0-7.0.1).
    Affected if Your installed version falls within any of the listed vulnerable ranges.
  4. Verify TFTP client functionality is accessible
    Check if the TFTP client is available on the system by attempting to invoke TFTP commands via CLI (for example, 'execute tftp' or reviewing system features). This is a local authenticated vulnerability requiring access to the TFTP client command line.
    Affected if The TFTP client is accessible to the local authenticated attacker.

You are affected if you run any of the eight Fortinet products within the specified version ranges and the TFTP client functionality is accessible to local authenticated users.

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 a release after 7.0.2
Interim mitigation

Upgrade FortiOS to version 6.4.7 or later, or version 7.0.3 or later. Since this requires authenticated local access, enforce least-privilege principles and monitor for suspicious TFTP client usage patterns.

Recommended fix High confidence

FortiOS: 6.4.8 or later, or 7.0.3 or later (other products upgrade to latest patched version)

  1. 1. Identify the specific Fortinet product (Fortiadc, Fortianalyzer, Fortimail, Fortimanager, Fortindr, FortiOS 6k7k, Fortiportal, or Fortiproxy) affected in your environment
  2. 2. Determine the currently installed version of the affected product
  3. 3. For FortiOS devices: upgrade to version 6.4.8 or higher, or version 7.0.3 or higher
  4. 4. For other affected products: upgrade to the latest available version that includes the security fix for CVE-2021-42757
  5. 5. Verify the upgrade was successful by checking the firmware version in the device GUI or CLI
  6. 6. Test that normal TFTP functionality continues to work as expected after the upgrade
Caveat Review Fortinet release notes for the target version to check for any configuration or feature changes that may affect your deployment

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

Fix this in Fortiadc Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing4.0 h
  • Review / QA2.0 h
12.0 hours of engineering $2,080
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Scan for this in your stack

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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-2021-42757 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