CVE-2023-51766 Security feature bypass in n/a

What is CVE-2023-51766?

CVE-2023-51766 is a medium-severity vulnerability in Debian Debian Linux, published on 24 Dec 2023. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official 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.

Weakness: CWE-345

Which versions are affected by CVE-2023-51766?

It affects 4 products.

Products include Debian Debian Linux, Exim Exim, Fedoraproject Extra Packages for Enterprise Linux, Fedoraproject Fedora.

How do I fix CVE-2023-51766?

Upgrade to a fixed version.

Is CVE-2023-51766 being exploited?

There is no known exploitation of CVE-2023-51766 in the wild and no public exploit code.

Other vulnerabilities in Debian Debian Linux

• CVE-2015-3306 ProFTPD Improper Access Control Exploited Critical 10.0
• CVE-2025-49113 RoundCube Webmail Deserialization of Untrusted Data Exploited Critical 9.9
• CVE-2026-24061 GNU InetUtils Argument Injection Exploited Critical 9.8
• CVE-2025-39682 Linux Kernel Improper Check for Unusual or Exceptional Conditions Exploited Critical 9.8
• CVE-2024-9680 Mozilla Firefox Use-After-Free Exploited Critical 9.8

All Debian Debian Linux vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as CLEANSTART-2025-LV68873, CLSA-2024-1709562273, CLSA-2024-1709563071, DEBIAN-CVE-2023-51766, DLA-3708-1, DSA-5597-1 and 5 more.