CVE-2021-43206Network attack vector

Client identity disclosure via proxy error pages

Published May 4, 2022 · Updated Oct 22, 2024

Information disclosure in Fortinet FortiOS and FortiProxy web proxies allows remote attackers to obtain a client's username and IP address. Proxy-generated HTTP error pages embed the client's username and IP address, and same-origin requests let a malicious webserver retrieve those pages. Exploitation requires a client behind an affected web proxy to visit an attacker-controlled webserver and trigger requests that produce proxy status-code pages.

CVSS severity4.3
Medium
EPSS probability0.81%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Information disclosure in Fortinet FortiOS and FortiProxy web proxies allows remote attackers to obtain a client's username and IP address. Proxy-generated HTTP error pages embed the client's username and IP address, and same-origin requests let a malicious webserver retrieve those pages. Exploitation requires a client behind an affected web proxy to visit an attacker-controlled webserver and trigger requests that produce proxy status-code pages.

The record

CVE
CVE-2021-43206
Published
May 4, 2022
Updated
Oct 22, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-550, CWE-209
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 4, 2022CVE publishedPublication date reported by the CVE source.
  2. Oct 22, 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?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

4.3NIST NVDAV:N/AC:M/Au:N/C:P/I:N/A:N
4.3FortinetCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/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)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-550Server-generated Error Message Containing Sensitive Information
CWE-209Generation of Error Message Containing Sensitive Information

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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