Cyber Resilience

CVE-2023-51766

MediumPublic PoC

Published: 24 December 2023

Published
24 December 2023
Modified
04 November 2025
KEV Added
Patch
CVSS Score v3.1 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
EPSS Score 0.0164 82.4th percentile
Risk Priority 12 60% EPSS · 20% KEV · 20% CVSS

Summary

CVE-2023-51766 is a medium-severity Insufficient Verification of Data Authenticity (CWE-345) vulnerability in Fedoraproject Extra Packages For Enterprise Linux. Its CVSS base score is 5.3 (Medium).

Operationally, ranked in the top 17.6% of CVEs by exploit likelihood; it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.

EU & UK References

Vulnerability details

Exim before 4.97.1 allows SMTP smuggling in certain PIPELINING/CHUNKING configurations. Remote attackers can use a published exploitation technique to inject e-mail messages with a spoofed MAIL FROM address, allowing bypass of an SPF protection mechanism. This occurs because Exim supports…

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<LF>.<CR><LF> but some other popular e-mail servers do not.

CWE(s)

Related Threats

No named actor attribution yet. ATT&CK technique mapping in progress for this CVE.

Affected Assets

exim
exim
≤ 4.97.1
fedoraproject
extra packages for enterprise linux
7.0, 8.0, 9.0
fedoraproject
fedora
38, 39
debian
debian linux
10.0

Mitigating Controls

Likely Mitigating Controls AI

Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.

addresses: CWE-345

Directly requires independent verification of matching output before adverse decisions, mitigating insufficient authenticity checks on data from external sources.

addresses: CWE-345

Use of approved PKI certificates provides verifiable data authenticity and origin for communications and artifacts.

addresses: CWE-345

Mandates provision of authenticity and integrity artifacts that enable verification of name/address resolution data.

addresses: CWE-345

Requires explicit verification of data authenticity from authoritative sources, preventing acceptance of unauthenticated resolution responses.

addresses: CWE-345

Control requires verification of data authenticity/integrity (e.g., checksums) after aggregation/packing, directly reducing exploitation of insufficient verification before transmission.

addresses: CWE-345

Time synchronization supports reliable freshness verification when checking data authenticity across systems or components.

addresses: CWE-345

Mandates verification of data authenticity for software, firmware, and information.

addresses: CWE-345

Provenance documentation and monitoring directly enables verification of authenticity for components and data throughout their history.

References