CVE-2020-28021Network attack vector

Authenticated root code execution via spool injection

Published May 6, 2021 · Updated Aug 4, 2024

Remote code execution in Exim 4 before 4.94.2 allows remote authenticated users to execute arbitrary commands as root via SMTP MAIL FROM. The AUTH= value is hex-decoded by auth_xtextdecode(), then authenticated_sender is written unescaped to a spool header, allowing injected lines to corrupt parsed header lengths and overwrite heap configuration strings. Valid SMTP credentials are required; delivery then expands an injected command expression with root privileges under the default privilege-drop setting.

CVSS severity8.8
High
EPSS probability4.14%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Remote code execution in Exim 4 before 4.94.2 allows remote authenticated users to execute arbitrary commands as root via SMTP MAIL FROM. The AUTH= value is hex-decoded by auth_xtextdecode(), then authenticated_sender is written unescaped to a spool header, allowing injected lines to corrupt parsed header lengths and overwrite heap configuration strings. Valid SMTP credentials are required; delivery then expands an injected command expression with root privileges under the default privilege-drop setting.

The record

CVE
CVE-2020-28021
Published
May 6, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
T1190
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. May 6, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

9.0NIST NVDAV:N/AC:L/Au:S/C:C/I:C/A:C
8.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

T1190Exploit Public-Facing Application

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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