CVE-2021-36167

Web-filter bypass via modified session identifier

Published Dec 9, 2021 · Updated Oct 25, 2024

Improper authorization in Fortinet FortiClient Windows 7.0.0, 6.4.0 through 6.4.6, and 6.2.0 through 6.2.8 allows attackers to bypass web filtering. The web filter accepts a modified session-id parameter without correctly authorizing it, allowing requests to evade configured URL controls. Local access to the client session is required, and the bounded impact is loss of web-filter policy enforcement rather than data disclosure or code execution.

CVSS severity4.3
Medium
EPSS probability0.57%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper authorization in Fortinet FortiClient Windows 7.0.0, 6.4.0 through 6.4.6, and 6.2.0 through 6.2.8 allows attackers to bypass web filtering. The web filter accepts a modified session-id parameter without correctly authorizing it, allowing requests to evade configured URL controls. Local access to the client session is required, and the bounded impact is loss of web-filter policy enforcement rather than data disclosure or code execution.

The record

CVE
CVE-2021-36167
Published
Dec 9, 2021
Updated
Oct 25, 2024
Vendor
Fortinet
Product
FortiClient Windows
Classifications
CWE-285, T1562.001
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 9, 2021CVE publishedPublication date reported by the CVE source.
  2. Oct 25, 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=FortiClientWindows 7.0.0, 6.4.6, 6.4.5, 6.4.4, 6.4.3, 6.4.2, 6.4.1, 6.4.0, 6.2.8, 6.2.7, 6.2.6, 6.2.5, 6.2.4, 6.2.3, 6.2.2, 6.2.1, 6.2.0

What conditions does exploitation require?

Attack vectorlocal
Required privilegesunauthenticated

What is affected?

Fortinet · FortiClient Windowsversion=FortiClientWindows 7.0.0, 6.4.6, 6.4.5, 6.4.4, 6.4.3, 6.4.2, 6.4.1, 6.4.0, 6.2.8, 6.2.7, 6.2.6, 6.2.5, 6.2.4, 6.2.3, 6.2.2, 6.2.1, 6.2.0

Published CVSS scores

4.3FortinetCVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:L
5.0NIST NVDAV:N/AC:L/Au:N/C:N/I:P/A:N
5.3NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

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)
Vectorlocal
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-285Improper Authorization
T1562.001Impair Defenses: Disable or Modify Tools

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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