CVE-2021-20501
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedIBM 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.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceIBM i SMTP servers with non-default configuration accept emails destined for non-existent local-domain recipients. This allows unauthenticated network attackers to relay spam through the server or consume disk space with undeliverable mail queue entries, exploiting the lack of proper recipient validation in the SMTP configuration.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data= 7.1= 7.2= 7.3= 7.4CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- Low
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Verify SMTP server is runningUse the command WRKCFGSTS *SMTP or check through System Service Tools (SST) to confirm the SMTP server configuration status is activeAffected if SMTP server is started and running - only running servers can be exploited
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Check SMTP recipient validation configurationUse WRKSMTPA or CHGSMTPA command to view SMTP attributes; look for settings related to recipient validation or address checking for local domainsAffected if The SMTP configuration does NOT validate that recipient addresses exist in local domains - messages for non-existent users are accepted rather than rejected
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Confirm SMTP accepts unauthenticated connectionsExamine SMTP server configuration for允许 anonymous or unauthenticated relay access; check whether authentication is required for SMTP submissionAffected if SMTP is configured to accept connections without authentication - this allows external attackers to relay mail through the server
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Inspect mail queue for undeliverable messagesUse WRKMSGQ or check the mail queue directories for buildup of messages to non-existent local recipientsAffected if The mail queue shows accumulation of undeliverable messages or messages to invalid local addresses indicating the vulnerability is being exploited
A user is affected if their IBM i SMTP server is running with recipient validation disabled or not properly configured, allowing acceptance of mail for non-existent local-domain users from unauthenticated connections.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
From vendor dataConfigure the IBM i SMTP server to validate recipients against the local domain and reject messages for non-existent users, and enable proper authentication to prevent unauthorized relay.
- Consultation3.0 h
- Implementation3.0 h
- Testing2.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,880.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-20501 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2021-20501 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.
- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
- No spam, self-promotion, credentials, or personal data