CVE-2020-28018
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 Use After Free in smtp_reset in certain situations that may be common for builds with OpenSSL.
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 · moderate confidenceExim 4 before 4.94.2 contains a Use After Free vulnerability in the smtp_reset function. This memory corruption issue occurs in specific scenarios that are common in builds using OpenSSL, potentially allowing remote attackers to execute arbitrary code via the freed memory reference.
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>= 4.90, < 4.94.2CVSS 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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Verify Exim versionRun 'exim --version' or check the exim binary with 'exim -bV' to identify the installed version numberAffected if Version is 4.90 through 4.94.1 (inclusive) - any version >= 4.90 but < 4.94.2 is affected
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Confirm Exim is actively runningCheck for running exim processes using 'ps aux | grep exim' or check if the SMTP service is listening on port 25Affected if Exim daemon is running with an affected version
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Identify if OpenSSL support is enabledReview Exim build configuration by running 'exim -bV' and look for OpenSSL or TLS in the compile-time features listAffected if Exim is built with OpenSSL support, which is a common condition for this vulnerability to be exploitable
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Check SMTP reset capabilityVerify the server accepts SMTP connections and can process RSET commands, which triggers the smtp_reset functionAffected if The SMTP service is exposed and accepts connections that could trigger the vulnerable smtp_reset code path
If Exim version is 4.90 through 4.94.1, is actively running as a mail server, and is built with OpenSSL support, the environment is likely affected by this Use After Free vulnerability.
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 · scoped4.94.2
Upgrade Exim to version 4.94.2 or later to resolve the Use After Free in smtp_reset. Given the critical CVSS score of 9.8, this upgrade should be prioritized for any affected mail servers.
Exim 4.94.2 or later
- 1. Check the current Exim version by running 'exim --version' or 'exim -v'
- 2. Stop the Exim service: 'systemctl stop exim' or 'service exim stop'
- 3. Update the package repository and upgrade Exim: On Debian/Ubuntu use 'apt-get update && apt-get install exim4', on RHEL/CentOS use 'yum update exim'
- 4. Verify the new version is 4.94.2 or later using 'exim --version'
- 5. Start the Exim service: 'systemctl start exim' or 'service exim start'
- 6. Test that mail functionality is working properly
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation4.0 h
- Implementation4.0 h
- Testing8.0 h
- Review / QA4.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2020-28018 — 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-2020-28018 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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- Version or environment caveats, and links to real fixes
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