LiveActive security incident?Get immediate response
CVE Record

CVE-2021-24020: A missing cryptographic step in the implementation of the hash digest algorithm in FortiMail 6.4.0 through...

A missing cryptographic step in the implementation of the hash digest algorithm in FortiMail 6.4.0 through 6.4.4, and 6.2.0 through 6.2.7 may allow an unauthenticated attacker to tamper with signed URLs by appending further data which allows bypass of signature verification.

HighCVSS 7.5Not KEV-listedUpdated
Discuss exposureBack to CVEs
Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

FortiMail versions 6.4.0 through 6.4.4 and 6.2.0 through 6.2.7 have a signed URL verification weakness. An attacker may be able to alter signed URLs by appending data, bypassing the signature check and potentially affecting sensitive email-security workflows.

Executive priority

Treat as high priority for organizations using affected FortiMail versions, especially internet-facing deployments. There is no cited active exploitation here, but the potential impact covers confidentiality, integrity, and availability.

Technical view

The issue is a missing cryptographic step in FortiMail’s hash digest implementation. Sources describe signature verification bypass through appended data on signed URLs. The CVSS 3.1 score is 7.5 high, with network attack vector, high attack complexity, no user interaction, and high confidentiality, integrity, and availability impact.

Likely exposure

Exposure is limited to Fortinet FortiMail deployments running 6.4.0-6.4.4 or 6.2.0-6.2.7. Risk depends on whether vulnerable signed URL handling is reachable in the deployed configuration.

Exploitation context

The source bundle does not show CISA KEV listing or cited active exploitation. The description says unauthenticated attacker, while the CVSS vector lists low privileges; treat that mismatch as an item to verify against Fortinet guidance.

Researcher notes

Key uncertainty is the privilege mismatch between the narrative and CVSS vector. Validate against Fortinet’s advisory before severity tuning. Do not assume other Fortinet products are affected from this source bundle.

Mitigation direction

  • Inventory FortiMail versions and flag 6.4.0-6.4.4 and 6.2.0-6.2.7.
  • Review Fortinet advisory FG-IR-21-027 for vendor-approved fixed releases or mitigations.
  • Plan remediation during the next security maintenance window unless exposure analysis shows immediate risk.
  • Limit reachable vulnerable signed-URL workflows where operationally possible until vendor guidance is applied.
  • Monitor FortiMail logs for unusual signed URL access patterns.

Validation and detection

  • Confirm FortiMail version from asset inventory or appliance management records.
  • Map whether signed URL functionality is enabled and externally reachable.
  • Compare deployed versions against the affected ranges in CVE-2021-24020.
  • Check Fortinet advisory FG-IR-21-027 for current remediation status.
  • Review security monitoring for anomalous URL tampering indicators.
Prepared
Confidence
medium
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.

cve · low confidence lookup

CVE-2021-24020 mapping review

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

Open ATT&CK lookup
Vulnerability profileCVE Program record
Severity
High
CVSS
7.5 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H

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
7.5CVSS 3.1HighCVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H1.65.9Primary CVE score

Vulnerability scoring details

Base CVSS 3.1 score

7.5High
CVSS 3.1 vector shape for CVE-2021-24020Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H

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 FortiMailFortiMail 6.4.0 through 6.4.4, and 6.2.0 through 6.2.7Listed
Weakness

CWE details

No CWE listed

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