CVE-2020-28017
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 · uneditedExim 4 before 4.94.2 allows Integer Overflow to Buffer Overflow in receive_add_recipient via an e-mail message with fifty million recipients. NOTE: remote exploitation may be difficult because of resource consumption.
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 confidenceExim 4 before 4.94.2 contains an integer overflow vulnerability in the receive_add_recipient function that can lead to a buffer overflow when processing an e-mail message with fifty million recipients. The integer counter overflows due to insufficient bounds checking, potentially allowing remote code execution or denial of service.
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< 4.94.1CVSS 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
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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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Check Exim installation and versionRun 'exim -v' or 'exim --version' to obtain the installed Exim version numberAffected if The reported version is less than 4.94.1 (e.g., 4.94, 4.93, 4.92, etc.)
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Verify Exim daemon is runningRun 'ps aux | grep exim' or 'systemctl status exim' to confirm the Exim MTA daemon is activeAffected if Exim is running and the version from step 1 is below 4.94.1
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Confirm SMTP listener is enabledCheck Exim configuration with 'exim -bV' or review /etc/exim/exim.conf for 'daemon_smtp_ports' to see if SMTP reception is enabledAffected if SMTP listener is enabled (typically port 25) and Exim version is below 4.94.1
The environment is affected if a running Exim version is below 4.94.1 and the SMTP service is available to accept incoming mail 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.
dbcve · scoped4.94.1
Upgrade Exim to version 4.94.2 or later to patch the integer overflow vulnerability in receive_add_recipient. Consider implementing recipient rate limiting or resource constraints to further mitigate potential exploitation attempts.
Exim 4.94.2 or later
- 1. Check current Exim version: exim -v -bV
- 2. Stop Exim service: systemctl stop exim (or service exim stop)
- 3. Back up current Exim configuration: cp -r /etc/exim /etc/exim.backup
- 4. Download Exim 4.94.2 or later from www.exim.org/ftp/exim/
- 5. Compile and install: ./configure --with-exim-user=exim && make && make install
- 6. Verify installed version: exim -bV
- 7. Start Exim service: systemctl start exim (or service exim start)
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation2.0 h
- Implementation2.0 h
- Testing3.0 h
- Review / QA1.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2020-28017 — 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-2020-28017 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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- 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
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