Security readout for executives and security teams
Plain-English summary
This issue can expose a web proxy user’s username and IP address through Fortinet-generated proxy error pages. A malicious website can receive that information if a user interacts with it and same-origin HTTP requests trigger proxy error responses. The business impact is limited data exposure, but it can weaken privacy and help attackers profile users or internal routing.
Executive priority
Treat this as a moderate-priority privacy and reconnaissance risk. It is not described as remote code execution or service disruption, but exposed usernames and IP addresses can aid targeting. Remediate during normal security maintenance, faster where proxy users include executives, administrators, or sensitive business units.
Technical view
CVE-2021-43206 is an information disclosure flaw in FortiOS and FortiProxy web proxy behavior. Server-generated HTTP status code pages may include sensitive client details, allowing malicious web servers to retrieve a proxy client username and IP through same-origin HTTP requests. CVSS 3.1 is 4.3 with network attack vector, low complexity, no privileges, and required user interaction.
Likely exposure
Exposure is most likely where affected FortiOS or FortiProxy versions are used as web proxies for users browsing external web content. Affected ranges include FortiOS 7.0.0-7.0.3, 6.4.0-6.4.8, 6.2.x, 6.0.x, listed 5.6.x versions, and FortiProxy 7.0.0-7.0.1 and 2.0.x.
Exploitation context
The provided sources do not show CISA KEV listing or confirmed active exploitation. Exploitation requires user interaction and a malicious web server, and the disclosed impact is confidentiality-only: username and IP exposure. The CVSS exploit maturity signal is proof-of-concept, but no exploit procedure is provided here.
Researcher notes
The source bundle’s title and description emphasize FortiOS 7.0, 6.4, 6.2, 6.0 and FortiProxy 7.0 and 2.0. The affected list also includes FortiOS 5.6.0 through 5.6.14. No CWE is provided. Validate against the Fortinet advisory before final scoping.
Mitigation direction
- Inventory FortiOS and FortiProxy versions used for web proxy services.
- Check Fortinet PSIRT FG-IR-21-231 for vendor-approved fixed releases or mitigations.
- Prioritize remediation for proxies serving internet-browsing users.
- Review whether affected proxy features are necessary until vendor guidance is applied.
- Avoid relying on unverified workarounds as complete remediation.
Validation and detection
- Confirm deployed FortiOS and FortiProxy versions against the affected version ranges.
- Identify systems providing web proxy functionality to user browsers.
- Review proxy error-page behavior only in controlled, authorized testing.
- Check logs for unusual external sites repeatedly causing proxy-generated error pages.
- Document remediation status against Fortinet advisory guidance.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CVE-2021-43206 mapping review
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Open ATT&CK lookup- Severity
- Medium
- CVSS
- 4.3 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N/E:P/RL:U/RC:C
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N/E:P/RL:U/RC:C2.81.4Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
4.3MediumVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N/E:P/RL:U/RC:C
Source materials
- CVE List V5 sourceCVE List V5
- https://fortiguard.com/psirt/FG-IR-21-231CVE reference · x_refsource_CONFIRM
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.