CVE-2023-42115Network attack vector

Unauthenticated code execution via EXTERNAL auth indexing

Published May 3, 2024 · Updated Sep 20, 2024

Out-of-bounds write in Exim before 4.96.1 allows remote attackers to execute arbitrary code through SMTP AUTH EXTERNAL requests. In src/src/auths/external.c, server_param2 expansion stores auth_vars at an attacker-influenced expand_nmax index without first resetting that index. Exploitation requires EXTERNAL authentication to be offered and runs code as the Exim service account; no authentication or user interaction is required.

CVSS severity9.8
Critical
EPSS probability9.96%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Out-of-bounds write in Exim before 4.96.1 allows remote attackers to execute arbitrary code through SMTP AUTH EXTERNAL requests. In src/src/auths/external.c, server_param2 expansion stores auth_vars at an attacker-influenced expand_nmax index without first resetting that index. Exploitation requires EXTERNAL authentication to be offered and runs code as the Exim service account; no authentication or user interaction is required.

The record

CVE
CVE-2023-42115
Published
May 3, 2024
Updated
Sep 20, 2024
Vendor
LibSPF2 Project
Product
Exim
Classifications
CWE-787, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 3, 2024CVE publishedPublication date reported by the CVE source.
  2. Sep 20, 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?

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

  1. Affected versionversion=0 <4.95
  2. Affected versionversion=exim 4.95

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

LibSPF2 Project · Eximversion=0 <4.95; version=exim 4.95

Published CVSS scores

9.8Zero Day InitiativeCVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
9.8UbuntuCVSS:3.0/AV:N/AC:L/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 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 exploitUnconfirmed

Weakness, pattern, technique

CWE-787Out-of-bounds Write
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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