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CVE Record

CVE-2021-20501: IBM i 7.1, 7.2, 7.3, and 7.4 SMTP allows a network attacker to send emails to non-existent local-domain rec...

IBM i 7.1, 7.2, 7.3, and 7.4 SMTP allows a network attacker to send emails to non-existent local-domain recipients to the SMTP server, caused by using a non-default configuration. An attacker could exploit this vulnerability to consume unnecessary network bandwidth and disk space, and allow remote attackers to send spam email. IBM X-Force ID: 198056.

MediumCVSS 5.9Not KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

IBM i SMTP can be abused when a non-default configuration accepts messages for non-existent local-domain recipients. A remote network attacker could waste bandwidth and disk space and potentially use the server to send spam. The issue is medium severity, focused on availability and abuse risk rather than data theft.

Executive priority

Treat this as a moderate operational risk. Prioritize exposed IBM i mail services because abuse can consume resources and damage email reputation, but current sources do not indicate data compromise or confirmed active exploitation.

Technical view

CVE-2021-20501 affects IBM i 7.1, 7.2, 7.3, and 7.4 SMTP. CVSS 3.0 is 5.9 with network access, no privileges, no user interaction, high attack complexity, no confidentiality or integrity impact, and high availability impact. IBM X-Force tracks it as 198056.

Likely exposure

Exposure is most likely where IBM i SMTP is enabled, reachable from untrusted networks, and configured with the affected non-default local-domain recipient behavior.

Exploitation context

The source bundle does not show CISA KEV listing or active exploitation. Exploitation is described as remote network abuse, but with high attack complexity and an unavailable exploit maturity signal.

Researcher notes

Key evidence is limited to the CVE description, CVSS vector, IBM advisory reference, and X-Force ID. The non-default configuration condition is central; avoid broad assumptions about all IBM i SMTP deployments without configuration validation.

Mitigation direction

  • Review IBM advisory 6445505 for release-specific fixes or configuration guidance.
  • Confirm whether IBM i SMTP uses the affected non-default configuration.
  • Restrict SMTP exposure to trusted mail relays where operationally possible.
  • Monitor mail queues, disk usage, and outbound spam complaints.
  • Prioritize unsupported IBM i releases for upgrade planning.

Validation and detection

  • Inventory IBM i 7.1, 7.2, 7.3, and 7.4 systems.
  • Identify systems with SMTP enabled and externally reachable.
  • Review SMTP configuration for non-default local-domain recipient handling.
  • Check mail queue growth, disk consumption, and rejected-recipient behavior.
  • Confirm IBM advisory remediation status for each affected host.
Prepared
Confidence
medium
Sources
4

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-2021-20501 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
5.9 (3.0)
Known Exploited
No
Published

Vector: CVSS:3.0/AV:N/C:N/S:U/AC:H/A:H/UI:N/I:N/PR:N/RC:C/E:U/RL:O

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
3Source 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
5.9CVSS 3.0MediumCVSS:3.0/AV:N/C:N/S:U/AC:H/A:H/UI:N/I:N/PR:N/RC:C/E:U/RL:O2.23.6Primary CVE score

Vulnerability scoring details

Base CVSS 3.0 score

5.9Medium
CVSS 3.0 vector shape for CVE-2021-20501Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.0/AV:N/C:N/S:U/AC:H/A:H/UI:N/I:N/PR:N/RC:C/E:U/RL:O

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
IBMi7.1, 7.2, 7.3, 7.4Listed
Weakness

CWE details

No CWE listed

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