CVE-2023-40718Network attack vector

Unauthenticated IPS evasion via TCP interpretation conflict

Published Oct 10, 2023 · Updated Sep 18, 2024

Interpretation conflict in Fortinet IPS Engine 7.321, 7.166, and 6.158 allows remote attackers to evade IPS inspection via crafted TCP packets. Fortinet has not disclosed which TCP field or parsing decision causes the engine and protected endpoint to interpret the packet differently. No authentication or user action is required; successful exploitation lets prohibited traffic cross the inspection boundary without triggering the intended IPS controls.

CVSS severity7.5
High
EPSS probability0.42%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Interpretation conflict in Fortinet IPS Engine 7.321, 7.166, and 6.158 allows remote attackers to evade IPS inspection via crafted TCP packets. Fortinet has not disclosed which TCP field or parsing decision causes the engine and protected endpoint to interpret the packet differently. No authentication or user action is required; successful exploitation lets prohibited traffic cross the inspection boundary without triggering the intended IPS controls.

The record

CVE
CVE-2023-40718
Published
Oct 10, 2023
Updated
Sep 18, 2024
Vendor
Fortinet
Product
IPS Engine
Classifications
CWE-436, T1562
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 10, 2023CVE publishedPublication date reported by the CVE source.
  2. Sep 18, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <=6.158
  2. Affected versionversion=0 <=7.166
  3. Affected versionversion=0 <=7.321
  4. Affected versionversion=6.158
  5. Affected versionversion=7.166
  6. Affected versionversion=7.321

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Fortinet · IPS Engineversion=0 <=6.158; version=0 <=7.166; version=0 <=7.321; version=6.158; version=7.166; version=7.321

Published CVSS scores

7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
6.7FortinetCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N/E:F/RL:O/RC:R

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-436Interpretation Conflict
T1562Impair Defenses

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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