How severe is CVE-2023-51766?

CVE-2023-51766 has a CVSS 3.x base score of 5.3, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity low, and availability none.

Is CVE-2023-51766 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (61st percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2023-51766?

CVE-2023-51766 primarily affects Exim. In total, 7 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2023-51766?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2023-51766 published?

CVE-2023-51766 was published on 2023-12-24 and last updated on 2026-06-17.

CVE-2023-51766

CVE-2023-51766 is a medium-severity vulnerability in Exim with a CVSS 3.x base score of 5.3. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-345.

Key facts

Severity: Medium (CVSS 3.x base score 5.3)
EPSS exploit prediction: 1% (61st percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-345
Affected product: Exim
Published: 2023-12-24
Last modified: 2026-06-17

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.

Frequently asked questions

What is CVE-2023-51766?: 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.
How severe is CVE-2023-51766?: CVE-2023-51766 has a CVSS 3.x base score of 5.3, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity low, and availability none.
Is CVE-2023-51766 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (61st percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2023-51766?: CVE-2023-51766 primarily affects Exim. In total, 7 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2023-51766?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2023-51766 published?: CVE-2023-51766 was published on 2023-12-24 and last updated on 2026-06-17.

References

Affected products (7)

cpe:2.3:a:exim:exim:*:*:*:*:*:*:*:*
cpe:2.3:a:fedoraproject:extra_packages_for_enterprise_linux:7.0:*:*:*:*:*:*:*
cpe:2.3:a:fedoraproject:extra_packages_for_enterprise_linux:8.0:*:*:*:*:*:*:*
cpe:2.3:a:fedoraproject:extra_packages_for_enterprise_linux:9.0:*:*:*:*:*:*:*
cpe:2.3:o:fedoraproject:fedora:38:*:*:*:*:*:*:*
cpe:2.3:o:fedoraproject:fedora:39:*:*:*:*:*:*:*
cpe:2.3:o:debian:debian_linux:10.0:*:*:*:*:*:*:*

More vulnerabilities in Exim

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CVE-2023-42115 — Critical (CVSS 9.8): Exim AUTH Out-Of-Bounds Write Remote Code Execution Vulnerability. This vulnerability allows remote attackers to…
CVE-2022-37452 — Critical (CVSS 9.8): Exim before 4.95 has a heap-based buffer overflow for the alias list in host_name_lookup in host.c when…
CVE-2020-28026 — Critical (CVSS 9.8): Exim 4 before 4.94.2 has Improper Neutralization of Line Delimiters, relevant in non-default configurations that enable…

All CVEs affecting Exim →

Other CWE-345 (Insufficient Verification of Data Authenticity) vulnerabilities

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CVE-2026-50195 — Critical (CVSS 9.9): containerd is an open-source container runtime. Versions prior to 2.3.2, 2.2.5 and 2.1.9 contain a vulnerability in the…
CVE-2022-36130 — Critical (CVSS 9.9): HashiCorp Boundary up to 0.10.1 did not properly perform data integrity checks to ensure the resources were associated…
CVE-2026-50214 — Critical (CVSS 9.8): The /v1/Plan service relies entirely on a shared global API token for full administrative management, allowing…
CVE-2025-15385 — Critical (CVSS 9.8): Insufficient Verification of Data Authenticity vulnerability in TECNO Mobile com.Afmobi.Boomplayer allows…

Browse all CWE-345 (Insufficient Verification of Data Authenticity) vulnerabilities →

Threat intelligence

Threat-intel indicators referencing this CVE:

193.202.11.112 (ipv4-addr)
76.12.128.249 (ipv4-addr)
50.116.72.139 (ipv4-addr)
166.62.41.190 (ipv4-addr)
160.187.147.124 (ipv4-addr)
132.148.155.138 (ipv4-addr)
77.221.151.241 (ipv4-addr)
37.221.254.200 (ipv4-addr)