CVE-2023-42118

Home/CVE/Exim libspf2 Integer Underflow Remote Code Execution Vulnerability. This vulnerability allows network-adjacent attackers

CVE

Exim libspf2 Integer Underflow Remote Code Execution Vulnerability. This vulnerability allows network-adjacent attackers

Exim libspf2 Integer Underflow Remote Code Execution Vulnerability. This vulnerability allows network-adjacent attackers to execute arbitrary code on affected installations of Exim libspf2. Authentication is not required to exploit this vulnerability.

The specific flaw exists within the parsing of SPF macros. When parsing SPF macros, the process does not properly validate user-supplied data, which can result in an integer underflow before writing to memory. An attacker can leverage this vulnerability to execute code in the context of the service account. .

Was ZDI-CAN-17578.

HIGH · CVSS 8.8 EPSS 0.51474

Act now

EPSS ≥ 0.50 - high probability of exploitation in the next 30 days
EPSS percentile: top 1% of all CVEs by exploitation likelihood
Public exploit or PoC is available
CVSS base score ≥ 7.0

Sigma rules0 YARA rules0

Look this up elsewhere - one-click external pivots

NVD CVE.org CISA Vulners Exploit-DB GitHub PoC VulnCheck KEV GreyNoise

▸ How to read a CVE - triage first, then detect and patch

This page is every public fact about CVE-2023-42118, cross-linked. Its job is to answer one question fast - does this need my attention now? - and then hand you the two things you do about it. Here is how an analyst reads it.

Triage: should I act now? Four signals, and they are not interchangeable:

CVSSseverity - how bad it is IF exploited, 0-10. A high CVSS alone is not urgency; a flaw can be a perfect 10 and never actually be attacked. EPSSprobability - a model’s estimate of the chance it is exploited in the next 30 days, 0-1. This is the “will it actually happen” signal. CISA KEVconfirmed - it is being exploited in the wild right now. The strongest signal on the page; KEV beats any score. Weaponisedavailability - public exploits / PoCs, and especially Metasploit modules rated Excellent / Great. Reliable, packaged exploit code means low-skill attackers can use it today.

How they combine: KEV, or a dependable Metasploit module, means patch now regardless of CVSS. High CVSS + low EPSS + no exploit is real but not an emergency - schedule it. Low CVSS but KEV-listed still gets patched now. The verdict above already weighed these for you; this is how it got there.

Then what - two workflows:

Detectwhen you cannot patch today, follow this CVE to the ATT&CK techniques it enables, then Build a SIEM detection (the green button) - author a rule, test it in Atomic, deploy it. That buys visibility while the patch waits. PatchAffected products / packages tell you if you are exposed; Fixed versions by distribution and Vendor advisories give the exact version that closes it.

Reading order for the panels below: verdict + badges, then Public exploits / Metasploit (is it weaponised), then ATT&CK techniques + Sigma / IDS rules (can I detect it), then Affected products / packages + Fixed versions (am I exposed, what patches it), then Threat actors / IOCs (who uses it), then Scoring & timeline / references (the evidence).

View attack path from CVE-2023-42118

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ATT&CK techniques

Techniques this CVE enables - linked via CWECAPECATT&CK. High◆ = named directly in ATT&CK or Nuclei templates.

T1210 · Exploitation of Remote Services

▤ Build a SIEM detection for these techniques

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Weakness Classification

CWE-191Integer Underflow (Wrap or Wraparound)

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Affected Products & Versions

libspf2 project libspf2all versions

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Affected Packages

Language-ecosystem packages (from OSV) tied to this CVE, with the version that fixes it - the dependency-level detail NVD doesn’t carry.

Ubuntu:20.04:LTS exim4

Ubuntu:20.04:LTS libspf2

Ubuntu:22.04:LTS exim4

Ubuntu:22.04:LTS libspf2

Ubuntu:24.04:LTS exim4

Ubuntu:24.04:LTS libspf2

Ubuntu:Pro:14.04:LTS exim4

Ubuntu:Pro:16.04:LTS exim4

Ubuntu:Pro:16.04:LTS libspf2

Ubuntu:Pro:18.04:LTS exim4

Ubuntu:Pro:18.04:LTS libspf2

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Public Exploits & PoCs

These PoC and exploit links come from public sources and are not verified to be safe or functional. Review the code before running anything, and treat unverified entries as untrusted.

pockrlabs/eximsmtp-vulnerabilities (trickest)

poczerodaygpt/Vulnerability-Management-Program-Implementation (trickest)

📦

Fixed versions by distribution

The package version that resolves this CVE on each Linux distribution, from the vendor’s published security data. fixed in shows a patched version exists; open means the package is listed as affected with no fix yet.

alpine edgelibspf2 fixed in 1.2.11-r3

alpine v3.19libspf2 fixed in 1.2.11-r3

alpine v3.20libspf2 fixed in 1.2.11-r3

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Scoring & Timeline

8.8

HIGH · CVSS v3.1 · [email protected]

View on NVD

Attack Vector

Network Adjacent Local Physical

Attack Complexity

Low High

Privileges Required

None Low High

User Interaction

None Required

Scope

Unchanged Changed

Confidentiality

None Low High

Integrity

None Low High

Availability

None Low High

Published to NVD03 May 2024 · 03:15 AM

CVSS VectorCVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

SSVC triage · cisa-vulnrichment

Exploitation

none

Automatable

Technical impact

total

SSVC asks the questions that actually drive patch urgency: is it being exploited, can attacks be automated, and how total is the impact.

🔗

References & Sources

Source URLs (vendor pages, mailing lists, write-ups). Exploit/PoC links are in their own section above to avoid duplication.

https://www.zerodayinitiative.com/advisories/ZDI-23-1472/Third Party Advisory

http://www.openwall.com/lists/oss-security/2025/03/28/1Mailing List