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Fortiweb CVE-2021-41027

HIGH
Out-of-bounds Write (CWE-787)
2021-12-08 psirt@fortinet.com
7.8
CVSS 3.1 · NVD
View

Vulnerability Assessment

Weakness
CWE
ASVS 5.0
V15 - Secure Coding and Architecture Bounds checking, write limits
MITRE ATT&CK

2 techniques across 2 tactics: Execution, Privilege Escalation

The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up.

Impact

CVSS score of 7.8 (HIGH). Attack characteristics: local attack vector, low complexity, low privileges required, no user interaction not required.

Exploit ScenarioDerived

A local attacker with access to the system could write data beyond allocated buffer boundaries leading to code execution or crashes.

This Week Schedule remediation this week. Why: HIGH severity (CVSS 7.0-8.9).
Patch available 0.2% exploitation probability (EPSS)

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AnalysisAI

A stack-based buffer overflow in Fortinet FortiWeb version 6.4.1 and 6.4.0, allows an authenticated attacker to execute unauthorized code or commands via crafted certificates loaded into the device. Rated high severity (CVSS 7.8), this vulnerability is low attack complexity. This Out-of-bounds Write vulnerability could allow attackers to write data beyond allocated buffer boundaries leading to code execution or crashes.

RemediationAI

A vendor patch is available. Apply the latest security update as soon as possible. Validate write boundaries, use memory-safe languages, enable compiler protections (ASLR, stack canaries).

Affects your stack

Find out whether the stacks and servers you run are on an affected version.

Checking this CVE against your own stacks and servers is part of the Basic plan and up.

Technical ContextAI · show details

This vulnerability is classified as Out-of-bounds Write (CWE-787), which allows attackers to write data beyond allocated buffer boundaries leading to code execution or crashes. A stack-based buffer overflow in Fortinet FortiWeb version 6.4.1 and 6.4.0, allows an authenticated attacker to execute unauthorized code or commands via crafted certificates loaded into the device. Affected products include: Fortinet Fortiweb. Version information: version 6.4.1.

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  • Exploit and PoC references, threat intelligence from 22 sources

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Severity by source

NVD PRIMARY 7.8 HIGH
AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Primary rating from NVD · only source for this CVE.

CVSS VectorNVD

Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

DescriptionNVD

A stack-based buffer overflow in Fortinet FortiWeb version 6.4.1 and 6.4.0, allows an authenticated attacker to execute unauthorized code or commands via crafted certificates loaded into the device.

Threat Intelligence Overview

EPSS Score
0.2%
Top 95% exploitable
Data Quality
2 sources
Confidence: Low

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue
Severity HIGH
CISA KEV No
Public POC No
EPSS 0.2%
Patch available Yes
Active threat No
Deciding rule
HIGH severity (CVSS 7.0-8.9)
What every action level means
Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.
Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.
This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.
This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.
Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision· derived
Defer
Exploitation· derived
None
System Exposure· derived
Small
Automatable· derived
No
Human Impact· derived
Medium

Priority Score

39
Low Medium High Critical
KEV: 0
EPSS: 0
CVSS: +39
PoC: 0
Weaponized: 0
Threat intel: 0
Gov advisory: 0

Attack Technique

A buffer overflow occurs when a program writes more data to a memory buffer than it was allocated to hold, causing the excess data to spill into adjacent memory regions.

Memory corruption occurs when a program writes data beyond the boundaries of allocated memory regions or accesses memory in unintended ways, violating the integrity of the process's address space.

Affected Products (CPE)NVD

cpe:2.3:a:fortinet:fortiweb:6.4.0:*:*:*:*:*:*:*
cpe:2.3:a:fortinet:fortiweb:6.4.1:*:*:*:*:*:*:*
CVE-2025-64446 CRITICAL POC
9.8 Nov 14

Fortinet FortiWeb contains a relative path traversal allowing unauthenticated attackers to execute administrative comman

CVE-2025-58034 HIGH POC
7.2 Nov 18

Fortinet FortiWeb contains an authenticated OS command injection allowing privilege escalation to execute unauthorized c

CVE-2025-52970 HIGH POC
8.1 Aug 12

A improper handling of parameters in Fortinet FortiWeb versions 7.6.3 and below, versions 7.4.7 and below, versions 7.2.

CVE-2024-48884 CRITICAL
9.1 Jan 14

Arbitrary file write and folder deletion in Fortinet FortiManager, FortiOS, and FortiProxy is possible via a path traver

CVE-2023-25610 CRITICAL
9.8 Mar 24

A buffer underwrite ('buffer underflow') vulnerability in the administrative interface of Fortinet FortiOS version 7.2.0

CVE-2021-22122 MEDIUM POC
6.1 Feb 08

An improper neutralization of input during web page generation in FortiWeb GUI interface 6.3.0 through 6.3.7 and version

CVE-2026-26035 CRITICAL
9.8 Aug 12

Authentication bypass in Fortinet FortiWeb (versions 7.0.0-7.0.12, 7.2.0-7.2.12, 7.4.0-7.4.11, 7.6.0-7.6.6, and 8.0.0-8.

CVE-2025-59719 CRITICAL
9.8 Dec 09

Authentication bypass in Fortinet FortiWeb 8.0.0, 7.6.0-7.6.4, and 7.4.0-7.4.9 allows unauthenticated remote attackers t

CVE-2021-41025 CRITICAL
9.8 Dec 08

Multiple vulnerabilities in the authentication mechanism of confd in FortiWeb versions 6.4.1, 6.4.0, 6.3.0 through 6.3.1

CVE-2021-36186 CRITICAL
9.8 Nov 02

A stack-based buffer overflow in Fortinet FortiWeb version 6.4.0, version 6.3.15 and below, 6.2.5 and below allows attac

CVE-2024-48885 CRITICAL
9.1 Jan 16

Privilege escalation via path traversal affects multiple Fortinet appliances - FortiWeb (6.4, 7.0, 7.2, 7.4.0-7.4.4, 7.6

CVE-2016-4066 HIGH
8.8 Jul 13

Cross-site request forgery (CSRF) vulnerability in Fortinet FortiWeb before 5.5.3 allows remote attackers to hijack the

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