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CVE Record

CVE-2021-42755: An integer overflow / wraparound vulnerability [CWE-190] in FortiSwitch 7.0.2 and below, 6.4.9 and below, 6...

An integer overflow / wraparound vulnerability [CWE-190] in FortiSwitch 7.0.2 and below, 6.4.9 and below, 6.2.x, 6.0.x; FortiRecorder 6.4.2 and below, 6.0.10 and below; FortiOS 7.0.2 and below, 6.4.8 and below, 6.2.10 and below, 6.0.x; FortiProxy 7.0.0, 2.0.6 and below, 1.2.x, 1.1.x, 1.0.x; FortiVoiceEnterprise 6.4.3 and below, 6.0.10 and below dhcpd daemon may allow an unauthenticated and network adjacent attacker to crash the dhcpd deamon, resulting in potential denial of service.

MediumCVSS 4.3Not KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

This flaw can let an unauthenticated attacker on an adjacent network crash Fortinet's DHCP daemon on affected products. The expected impact is denial of service, not data theft or takeover, but DHCP disruption can affect network availability.

Executive priority

Handle as a moderate availability issue. It is not described as remote takeover, but DHCP outages can disrupt business connectivity, especially in branch, campus, or voice environments using affected Fortinet platforms.

Technical view

CVE-2021-42755 is a CWE-190 integer overflow or wraparound in the dhcpd daemon across listed Fortinet FortiSwitch, FortiRecorder, FortiOS, FortiProxy, and FortiVoiceEnterprise versions. CVSS 3.1 is 4.3: adjacent attack vector, low complexity, no privileges, no user interaction, availability impact only.

Likely exposure

Exposure is most likely where affected Fortinet appliances run vulnerable versions and their DHCP service is reachable from adjacent network segments. The provided data does not identify internet-routable exploitation.

Exploitation context

The bundle marks CISA KEV as false. The CVSS vector includes E:F, but no provided source confirms active exploitation, weaponization, or observed attacks. Treat this as a plausible adjacent-network denial-of-service risk.

Researcher notes

Evidence is limited to the CVE record and Fortinet PSIRT reference. The affected range is broad across several product families. Validation should focus on version confirmation, DHCP role, and adjacent-network reachability rather than internet exposure assumptions.

Mitigation direction

  • Review Fortinet PSIRT FG-IR-21-155 for fixed versions and upgrade guidance.
  • Prioritize affected systems providing DHCP for critical network segments.
  • Restrict DHCP exposure to trusted network segments where operationally possible.
  • Monitor Fortinet advisories for updated remediation or workaround instructions.

Validation and detection

  • Inventory FortiSwitch, FortiRecorder, FortiOS, FortiProxy, and FortiVoiceEnterprise versions.
  • Compare installed versions against the affected ranges in CVE-2021-42755.
  • Confirm which devices run DHCP services on reachable interfaces.
  • Check logs and monitoring for unexpected dhcpd restarts or availability drops.
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

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

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CVE-2021-42755 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

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Vulnerability profileCVE Program record
Severity
Medium
CVSS
4.3 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L/E:F/RL:U/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
4.3CVSS 3.1MediumCVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L/E:F/RL:U/RC:C2.81.4Primary CVE score

Vulnerability scoring details

Base CVSS 3.1 score

4.3Medium
CVSS 3.1 vector shape for CVE-2021-42755Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L/E:F/RL:U/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 FortiSwitch, FortiRecorder, FortiVoiceEnterprise, FortiOS, FortiProxyFortiSwitch 7.0.2 and below, 6.4.9 and below, 6.2.x, 6.0.x; FortiRecorder 6.4.2 and below, 6.0.10 and below; FortiOS 7.0.2 and below, 6.4.8 and below, 6.2.10 and below, 6.0.x; FortiProxy 7.0.0, 2.0.6 and below, 1.2.x, 1.1.x, 1.0.x; FortiVoiceEnterprise 6.4.3 and below, 6.0.10 and belowListed
Weakness

CWE details

No CWE listed

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