CVE-2020-26099
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 · uneditedcPanel before 88.0.3 allows attackers to bypass the SMTP greylisting protection mechanism (SEC-491).
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 confidencecPanel versions before 88.0.3 contain a vulnerability that allows attackers to bypass the SMTP greylisting protection mechanism. Greylisting is an anti-spam technique that temporarily rejects first-time email senders; bypassing this control could enable spam relaying or unauthorized email transmission.
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< 88.0.3CVSS 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
- High
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
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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Check installed cPanel versionRun command: /usr/local/cpanel/version or access WHM > Server Information > cPanel versionAffected if The version number is lower than 88.0.3 (for example 88.0.2, 88.0.1, 88.0.0, or any 86.x, 84.x version)
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Confirm greylisting is enabledIn WHM, navigate to Email > Greylisting and verify the feature is turned ON, or check Exim configuration for greylisting directivesAffected if Greylisting is actively enabled on the server (the bypass only affects servers using greylisting)
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Review Exim logs for greylisting bypass attemptsExamine /var/log/exim_mainlog for patterns where emails are being accepted without the expected greylisting deferral, looking for first-time senders that bypass the 5-15 minute delayAffected if You find entries where remote servers connect and deliver immediately without being temporarily rejected (code 450 defer) on first attempt
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Check for unauthorized email relay activityReview /var/log/exim_mainlog and mail queue (exim -bp) for unusual outbound email patterns from untrusted sourcesAffected if There is evidence of spam or bulk email being relayed through your server that should have been blocked by greylisting
You are affected if your cPanel version is below 88.0.3 AND greylisting is enabled, because attackers could have bypassed the temporary rejection and delivered spam or unauthorized emails.
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 data88.0.3
Upgrade cPanel to version 88.0.3 or later to restore proper greylisting protection.
- Consultation2.0 h
- Implementation2.0 h
- Testing2.0 h
- Review / QA1.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2020-26099 — 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-2020-26099 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