CVE-2023-42117Network attack vector

Remote code execution via malformed PROXY addresses

Published May 3, 2024 · Updated Nov 3, 2025

Memory corruption in Exim before 4.96.2 allows remote attackers to execute code through crafted PROXY protocol address data. The SMTP receiver relies on string_is_ip_address() to validate proxy-supplied addresses, but the pre-fix parser fails to reject malformed special-element input. Reachability requires Exim to trust an untrusted PROXY protocol proxy; ordinary direct SMTP clients cannot reach the flawed path.

CVSS severity8.1
High
EPSS probability5.72%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Memory corruption in Exim before 4.96.2 allows remote attackers to execute code through crafted PROXY protocol address data. The SMTP receiver relies on string_is_ip_address() to validate proxy-supplied addresses, but the pre-fix parser fails to reject malformed special-element input. Reachability requires Exim to trust an untrusted PROXY protocol proxy; ordinary direct SMTP clients cannot reach the flawed path.

The record

CVE
CVE-2023-42117
Published
May 3, 2024
Updated
Nov 3, 2025
Vendor
LibSPF2 Project
Product
Exim
Classifications
CWE-138, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 3, 2024CVE publishedPublication date reported by the CVE source.
  2. Nov 3, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=-
  2. Affected versionversion=4.96-RC1-11-315206fbf

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

LibSPF2 Project · Eximversion=-; version=4.96-RC1-11-315206fbf

Published CVSS scores

8.1Zero Day InitiativeCVSS:3.1/AV:N/AC:H/PR:N/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
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-138Improper Neutralization of Special Elements
T1190Exploit Public-Facing Application

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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