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EximApplication

CVE-2020-28026

CRITICAL · 9.8 CVSS v3.1 Published 2021-05-06
Fix available
A fix is available. Upgrade to 4.94.2 or later.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click

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 · unedited
Exim 4 before 4.94.2 has Improper Neutralization of Line Delimiters, relevant in non-default configurations that enable Delivery Status Notification (DSN). Certain uses of ORCPT= can place a newline into a spool header file, and indirectly allow unauthenticated remote attackers to execute arbitrary commands as root.

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 confidence

Exim 4 before 4.94.2 allows unauthenticated remote command injection via improper handling of the ORCPT parameter in Delivery Status Notification (DSN) headers. Attackers can inject newline characters into mail spool header files, potentially executing arbitrary commands as root.

MitigationUpgrade Exim to version 4.94.2 or later. If immediate patching is not feasible, disable DSN (a non-default feature) as a temporary workaround.

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
EximApplication
Affected:>= 4.00, < 4.94.2

CVSS 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 checks

Work through these to decide whether this CVE applies to you.

  1. Check installed Exim version
    Run `exim -v` or `exim --version` to obtain the exact version number, or query the package manager (e.g., `dpkg -l exim4` on Debian/Ubuntu, `rpm -q exim` on RHEL/CentOS)
    Affected if The installed version is 4.00 or higher but lower than 4.94.2 (the vulnerable version range)
  2. Verify DSN feature status
    Inspect the Exim configuration file (typically /etc/exim/exim.conf, /etc/exim4/exim4.conf, or /etc/exim/exim4.conf.template) for the `dsn_notify` directive. Also check for any custom router or transport that processes DSN requests
    Affected if DSN is explicitly enabled via dsn_notify or related configuration (this feature must be active for the vulnerability to be exploitable)
  3. Confirm Exim is accepting external connections
    Check if Exim is listening on port 25 or other mail ports by running `netstat -tlnp | grep exim` or `ss -tlnp | grep exim`, and verify the daemon is actively running with `systemctl status exim` or `systemctl status exim4`
    Affected if Exim daemon is running and accessible over the network (the vulnerability is remotely exploitable without authentication)

The environment is affected if Exim version is 4.00 through 4.94.1 AND the DSN feature is enabled in the configuration, allowing remote unauthenticated attackers to inject commands via malicious ORCPT parameters.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

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 · scoped
Upgrade available Upgrade to 4.94.2 or later
Fixed in 4.94.2
Interim mitigation

Upgrade Exim to version 4.94.2 or later. If immediate patching is not feasible, disable DSN (a non-default feature) as a temporary workaround.

Recommended fix High confidence

Exim 4.94.2 or later

  1. 1. Check current Exim version using 'exim -v' or 'exim --version'
  2. 2. Backup current Exim configuration files (typically in /etc/exim/ or /etc/exim4/)
  3. 3. Use your system's package manager to upgrade Exim (e.g., apt-get update && apt-get install exim4, yum update exim, or dnf update exim)
  4. 4. Verify the new version is 4.94.2 or later using 'exim --version'
  5. 5. Test mail functionality to ensure Exim is operating correctly after upgrade
  6. 6. If using DSN (Delivery Status Notification), verify the configuration does not use the vulnerable ORCPT= parameter handling
Caveat Minimal - this is a security-focused point release; however, test mail flow after upgrade in non-production first

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Exim Scoped from the published advisory
  • Consultation2.0 h
  • Implementation2.0 h
  • Testing3.0 h
  • Review / QA2.0 h
9.0 hours of engineering $1,570
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2020-28026 in production — separate from our analysis above.

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What this is

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.

What belongs here
  • 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