CVE-2020-28020Public exploitNetwork attack vector

Unauthenticated code execution via header-size integer overflow

Published May 6, 2021 · Updated Aug 4, 2024

Integer overflow in receive_msg() in Exim before 4.92 allows remote attackers to execute arbitrary code through crafted SMTP headers. Continuation-only header lines bypass header_maxsize, causing header_size to double past INT_MAX and become negative before allocation and memcpy operations. No authentication or user interaction is required; successful exploitation executes commands as the Exim service user and can crash the receive process.

CVSS severity9.8
Critical
EPSS probability7.94%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Integer overflow in receive_msg() in Exim before 4.92 allows remote attackers to execute arbitrary code through crafted SMTP headers. Continuation-only header lines bypass header_maxsize, causing header_size to double past INT_MAX and become negative before allocation and memcpy operations. No authentication or user interaction is required; successful exploitation executes commands as the Exim service user and can crash the receive process.

The record

CVE
CVE-2020-28020
Published
May 6, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-190, T1190
Attack vector
network
Privileges
unauthenticated

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 privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

9.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
7.5NIST NVDAV:N/AC:L/Au:N/C:P/I:P/A:P

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.

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-190Integer Overflow or Wraparound
T1190Exploit Public-Facing Application

Public exploit references

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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