CVE-2020-28019
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 Initialization that can lead to recursion-based stack consumption or other consequences. This occurs because use of certain getc functions is mishandled when a client uses BDAT instead of DATA.
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 version 4.94.2 has an improper initialization vulnerability where getc function handling is mishandled when clients use the BDAT command (chunked transfer) instead of DATA. This can cause recursion-based stack consumption leading to denial of service or other unintended consequences.
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>= 4.88, < 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
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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 installed Exim versionRun `exim -v -V` or `exim --version` to display the Exim version number. On RPM-based systems, use `rpm -q exim`. On Debian-based systems, use `dpkg -l exim`.Affected if The version is greater than or equal to 4.88 but less than 4.94.2 (for example, 4.92, 4.93, 4.94, 4.94.1).
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Verify BDAT command support is enabledExamine the Exim configuration file (typically /etc/exim/exim.conf or /etc/exim4/exim4.conf) for the presence of the `begin BDAT` or `BDAT` router/transport directive, or check if chunking is advertised in SMTP capabilities by connecting to the server and checking the EHLO response for CHUNKING support.Affected if BDAT/chunking is enabled and advertised in SMTP capabilities (the vulnerability triggers when clients use BDAT instead of DATA).
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Identify active SMTP listeners accepting external connectionsCheck Exim configuration for listening daemons: look for `daemon_smtp_ports` or `tls_on_connect_ports` directives, and verify with `netstat -tlnp | grep exim` or `ss -tlnp | grep exim` whether Exim is bound to port 25 or other SMTP ports.Affected if Exim is running as a daemon listening on SMTP ports and accepting external connections (the flaw is triggerable via network by sending BDAT commands).
You are affected if your Exim version falls within 4.88 through 4.94.1 inclusive and the server has BDAT/chunking support enabled and accessible to remote clients.
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 data4.94.2
Upgrade Exim to version 4.94.2 or later to obtain the patched code that properly handles getc functions during BDAT processing.
- Consultation1.0 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-2020-28019 — 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-2020-28019 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
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