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FortiosOperating system · Fortinet

CVE-2020-15938

HIGH · 7.5 CVSS v3.1 Published 2021-03-04
Fix available
A fix is available. Upgrade to after 6.4.2 or later.
See remediation →
84/100
Remediation priority · High
Remotely reachable 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
When traffic other than HTTP/S (eg: SSH traffic, etc...) traverses the FortiGate in version below 6.2.5 and below 6.4.2 on port 80/443, it is not redirected to the transparent proxy policy for processing, as it doesn't have a valid HTTP header.

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

FortiGate transparent proxy fails to intercept non-HTTP/S traffic (e.g., SSH) on ports 80/443 because the proxy only processes requests with valid HTTP headers, allowing such traffic to bypass proxy policy enforcement.

MitigationUpgrade FortiGate to version 6.2.5 or 6.4.2 or later to remediate this transparent proxy bypass vulnerability.

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:<= 6.2.5>= 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
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
High
Availability
None

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

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. Check FortiOS version
    Run 'get system status' in FortiGate CLI to retrieve the installed FortiOS version
    Affected if The version is 6.2.5 or lower, or 6.4.0 through 6.4.2 (inclusive)
  2. Verify transparent proxy is enabled
    Run 'show firewall transparent-mode' in FortiGate CLI to check if transparent mode is active
    Affected if Transparent mode is enabled on the FortiGate device
  3. Confirm proxy policy on ports 80/443
    Run 'show firewall proxy-policy' in FortiGate CLI to list proxy policies and identify if any intercept traffic on ports 80/443
    Affected if A proxy policy exists that handles HTTP/HTTPS traffic on ports 80/443
  4. Test non-HTTP traffic interception
    Generate non-HTTP traffic (such as SSH on port 443) directed through the FortiGate and use 'diag sniffer packet' to observe whether the proxy policy is applied or the traffic flows unimpeded
    Affected if Non-HTTP traffic on ports 80/443 bypasses the proxy policy and is not inspected

The environment is affected if FortiOS version falls within the vulnerable range AND transparent proxy is configured to handle traffic on ports 80/443, allowing non-HTTP traffic to bypass proxy enforcement.

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.

From vendor data
Upgrade available Upgrade to a release after 6.4.2
Interim mitigation

Upgrade FortiGate to version 6.2.5 or 6.4.2 or later to remediate this transparent proxy bypass vulnerability.

Fix this in Fortios Scoped from the published advisory
  • Consultation2.0 h
  • Implementation3.0 h
  • Testing3.0 h
  • Review / QA1.0 h
9.0 hours of engineering $1,570
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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-2020-15938 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