Is CVE-2023-51766 actively exploited?

CVE-2023-51766 has no public evidence of in-the-wild exploitation as of 2025-11-04.

What is the CVSS score for CVE-2023-51766?

CVE-2023-51766 has a CVSS score of 5.3 (MEDIUM severity). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N.

How do I patch CVE-2023-51766?

Patch guidance is available from exim security advisories. CVEDatabase generates AI-assisted remediation guidance on demand for CVE-2023-51766.

CVE-2023-51766 - remediation guidance & executive summary

Q: Which products are affected by CVE-2023-51766?

7 products: exim exim, fedoraproject extra packages for enterprise linux, fedoraproject extra packages for enterprise linux, fedoraproject extra packages for enterprise linux, fedoraproject fedora, and 2 more.

Description

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

CVSS Metrics

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Attack Vector: network
Complexity: low
Privileges: none
User Action: none
Scope: unchanged
Confidentiality: none
Integrity: low
Availability: none
Weaknesses: CWE-345

Metadata

Primary Vendor: EXIM
Published: 12/24/2023
Last Modified: 11/4/2025
Source: NIST NVD
Note: Verify all details with official vendor sources before applying patches.

Affected Products

exim : eximfedoraproject : extra_packages_for_enterprise_linuxfedoraproject : extra_packages_for_enterprise_linuxfedoraproject : extra_packages_for_enterprise_linuxfedoraproject : fedorafedoraproject : fedoradebian : debian_linux

Remediation Guidance

Executive Summary

View on NIST NVD