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CVE Record

CVE-2021-36191: A url redirection to untrusted site ('open redirect') in Fortinet FortiWeb version 6.4.1 and below, 6.3.15...

A url redirection to untrusted site ('open redirect') in Fortinet FortiWeb version 6.4.1 and below, 6.3.15 and below allows attacker to use the device as proxy via crafted GET parameters in requests to error handlers

MediumCVSS 4.1Not KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

This Fortinet FortiWeb issue can let an attacker abuse the appliance as an open redirect through crafted GET parameters sent to error handlers. The business risk is mainly phishing, trust abuse, and traffic redirection using a legitimate FortiWeb hostname, not data theft or service outage.

Executive priority

Handle as a medium-priority brand and phishing-risk issue. It is not described as remote code execution or data disclosure, but exposed FortiWeb systems could help attackers make malicious links look more trustworthy.

Technical view

CVE-2021-36191 is an open redirect in FortiWeb 6.4.1 and below, 6.3.15 and below, and older listed 6.x versions. CVSS 3.1 is 4.1 with network access, low complexity, low privileges, user interaction required, changed scope, and low integrity impact.

Likely exposure

Organizations running Fortinet FortiWeb versions listed in the CVE source are potentially exposed. Internet-facing FortiWeb deployments carry higher practical risk because attackers can make redirected links appear to originate from a trusted security appliance domain.

Exploitation context

The bundle does not show CISA KEV listing or cited evidence of active exploitation. CVSS records exploit code maturity as proof-of-concept, but the provided sources do not include exploit details. Abuse requires crafted requests and user interaction, with limited integrity impact.

Researcher notes

Evidence is limited to the CVE record and Fortinet advisory reference. The vulnerability is categorized as URL redirection to an untrusted site through error-handler GET parameters. Avoid assuming broader proxying, authentication bypass, or exploitation in the wild without additional sourced evidence.

Mitigation direction

  • Inventory FortiWeb deployments and record exact software versions.
  • Check Fortinet advisory FG-IR-21-133 for fixed releases or vendor mitigation guidance.
  • Prioritize remediation for internet-facing FortiWeb instances.
  • Monitor requests to error handlers for unusual external redirect parameters.
  • Do not rely on the affected device hostname as proof of link safety.

Validation and detection

  • Compare installed FortiWeb versions against the affected version list.
  • Confirm whether each affected instance is externally reachable.
  • Review logs for suspicious error-handler requests with redirect-like GET parameters.
  • After remediation, verify the version no longer matches the affected list.
Prepared
Confidence
high
Sources
3

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

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

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CVE-2021-36191 mapping review

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Vulnerability profileCVE Program record
Severity
Medium
CVSS
4.1 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:N/I:L/A:N/E:P/RL:X/RC:C

Official CVE source material

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.

1CVSS vectors
0Timeline events
0ADP providers
2Source links

CVSS vector scores

1 official score

We 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.

ScoreVersionSeverityVectorExploitImpactSource
4.1CVSS 3.1MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:N/I:L/A:N/E:P/RL:X/RC:C2.31.4Primary CVE score

Vulnerability scoring details

Base CVSS 3.1 score

4.1Medium
CVSS 3.1 vector shape for CVE-2021-36191Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:N/I:L/A:N/E:P/RL:X/RC:C

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
FortinetFortinet FortiWebFortiWeb 6.4.1, 6.4.0, 6.3.15, 6.3.14, 6.3.13, 6.3.12, 6.3.11, 6.3.10, 6.3.9, 6.3.8, 6.3.7, 6.3.6, 6.3.5, 6.3.4, 6.3.3, 6.3.2, 6.3.1, 6.3.0, 6.2.6, 6.2.5, 6.2.4, 6.2.3, 6.2.2, 6.2.1, 6.2.0, 6.1.2, 6.1.1, 6.1.0, 6.0.7, 6.0.6, 6.0.5, 6.0.4, 6.0.3, 6.0.2, 6.0.1, 6.0.0Listed
Weakness

CWE details

No CWE listed

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.