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FortiosOperating system · Fortinet

CVE-2015-5965

MEDIUM · 5.0 CVSS v2.0 Published 2015-08-11
Fix available
A fix is available. Upgrade to after 4.3.12 or later.
See remediation →
59/100
Remediation priority · Elevated
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
The SSL-VPN feature in Fortinet FortiOS before 4.3.13 only checks the first byte of the TLS MAC in finished messages, which makes it easier for remote attackers to spoof encrypted content via a crafted MAC field.

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

The SSL-VPN feature in Fortinet FortiOS before 4.3.13 has a flawed MAC verification where only the first byte of the TLS MAC is checked in finished messages. This allows remote attackers to bypass authentication of TLS finished messages and spoof encrypted content by crafting a MAC field with a matching first byte.

MitigationUpgrade FortiOS to version 4.3.13 or later to implement full MAC validation in TLS finished message verification.

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:<= 4.3.12

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
Authentication
None
Confidentiality
None
Integrity
Partial
Availability
None

AV:N/AC:L/Au:N/C:N/I:P/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 firmware version
    Run 'get system status' via CLI or check System > FortiGuard in the web GUI to view the current firmware version
    Affected if Version is 4.3.12 or lower (the displayed version number is less than or equal to 4.3.12)
  2. Confirm SSL-VPN feature is enabled
    Run 'get vpn ssl settings' via CLI or check VPN > SSL-VPN in the web GUI to see if SSL-VPN is configured and active
    Affected if SSL-VPN is enabled and the status shows it is operational or configured for use

Your environment is affected if the FortiOS version is 4.3.12 or lower AND the SSL-VPN feature is enabled or has been used.

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 4.3.12
Interim mitigation

Upgrade FortiOS to version 4.3.13 or later to implement full MAC validation in TLS finished message verification.

Fix this in Fortios Scoped from the published advisory
  • Consultation3.0 h
  • Implementation6.0 h
  • Testing3.0 h
  • Review / QA2.0 h
14.0 hours of engineering $2,490
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,984.

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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-2015-5965 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