CVE-2020-28022
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 has Improper Restriction of Write Operations within the Bounds of a Memory Buffer. This occurs when processing name=value pairs within MAIL FROM and RCPT TO commands.
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 a buffer write vulnerability where improper bounds checking occurs when parsing name=value pairs in MAIL FROM and RCPT TO SMTP commands. This allows writing data beyond allocated memory buffer boundaries, potentially enabling remote code execution or service disruption.
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>= 4.00, < 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.
-
Identify Exim versionRun 'exim -v -bV' or check the exim binary version with 'exim --version' to get the installed version numberAffected if Version is 4.00 or higher but lower than 4.94.2
-
Confirm Exim is running as SMTP serverCheck if exim process is listening on SMTP ports (25, 587, or custom SMTP ports) using 'netstat -tlnp | grep exim' or 'ss -tlnp | grep exim'Affected if Exim is actively listening for incoming SMTP connections
-
Verify ESMTP extensions are enabledConnect to the SMTP server (e.g., 'telnet localhost 25' or 'openssl s_client -connect localhost:25 -starttls smtp') and issue EHLO to list available extensionsAffected if Server responds with EHLO and supports MAIL FROM or RCPT TO commands that accept name=value style parameters (common in ESMTP extensions like SIZE, BODY, or AUTH)
Your environment is affected if Exim version is 4.00 through 4.94.1 and the server accepts SMTP connections with ESMTP extensions that handle name=value pairs in MAIL FROM or RCPT TO commands.
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. If immediate patching is not possible, consider implementing SMTP command filtering at the perimeter or disabling unnecessary SMTP extensions that accept name=value pairs.
4.94.2 or later
- Check current Exim version using: exim -v 2>&1 | head -1 or exim --version
- Verify the version is affected (>= 4.00 and < 4.94.2)
- Obtain Exim 4.94.2 or later from your distribution's package manager or www.exim.org
- Upgrade Exim using your package manager (e.g., apt-get update && apt-get install exim4 for Debian/Ubuntu, or yum/dnf update exim for RHEL/CentOS)
- Restart Exim service: systemctl restart exim or service exim restart
- Verify the new version is installed and running: exim --version
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation2.0 h
- Implementation2.0 h
- Testing2.0 h
- Review / QA1.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,984.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2020-28022 — 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-2020-28022 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
Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.
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