sendmail through 8.17.2 allows SMTP smuggling in certain configurations.
Key facts
- Attack vector
- Network
- Privileges required
- None
- User interaction
- None
- Attack complexity
- Low
- Impact type
- Security bypass
- Confidentiality · integrity · availability
- None · Low · None
- Fix status
- Will not fix Red Hat: no fix planned
Attack profile from CVSS 3.1 · NVD. Fix status from CNA and Red Hat. Impact type from CWE-345.
Summary
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.
Why it matters now
SSVC decision points
Not available: CISA has not published SSVC decision points for this record.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| — | — | all versions | — | No fix listed | CNA |
- — Vendor— Affected all versions Fixed in — No fix listed CNA
CPE configurations NVD · 4
| CPE | Versions | Role | Vendor |
|---|---|---|---|
| cpe:2.3:a:sendmail:sendmail:*:*:*:*:*:*:*:* | before 8.18.0.2 | Vulnerable | Sendmail |
| cpe:2.3:o:freebsd:freebsd:*:*:*:*:*:*:*:* | before 11.0 | Vulnerable | FreeBSD |
| cpe:2.3:o:redhat:enterprise_linux:8.0:*:*:*:*:*:*:* | 8.0 | Vulnerable | Red Hat |
| cpe:2.3:o:redhat:enterprise_linux:9.0:*:*:*:*:*:*:* | 9.0 | Vulnerable | Red Hat |
- cpe:2.3:a:sendmail:sendmail:*:*:*:*:*:*:*:* Versions before 8.18.0.2 Vulnerable ·Sendmail
- cpe:2.3:o:freebsd:freebsd:*:*:*:*:*:*:*:* Versions before 11.0 Vulnerable ·FreeBSD
- cpe:2.3:o:redhat:enterprise_linux:8.0:*:*:*:*:*:*:* Versions 8.0 Vulnerable ·Red Hat
- cpe:2.3:o:redhat:enterprise_linux:9.0:*:*:*:*:*:*:* Versions 9.0 Vulnerable ·Red Hat
Remediation
No fixed version listed by the sources yet.
Vendor assessments
Red Hat
Red Hat rating: Moderate. Red Hat's page for this CVE →
| Product | Status | Plan or fix |
|---|---|---|
| Red Hat Enterprise Linux 6 | Affected | No fix planned: Out of support scope |
| Red Hat Enterprise Linux 7 | Affected | No fix planned: Out of support scope |
| Red Hat Enterprise Linux 8 | Affected | No fix planned: Will not fix |
| Red Hat Enterprise Linux 9 | Affected | No fix planned: Will not fix |
Timeline
- 2026-10-02 Threatist record created from CVE-2023-51765
- 2026-10-03 Alias added: GHSA-5rcq-25vc-g8qr
References
Patch 2
Advisory 11
- 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
- [oss-security] 20231224 Re: Re: New SMTP smuggling attack
- [oss-security] 20231225 Re: Re: New SMTP smuggling attack
- https://bugzilla.redhat.com/show_bug.cgi?id=2255869
- https://access.redhat.com/security/cve/CVE-2023-51765
- [oss-security] 20231226 Re: New SMTP smuggling attack
- [oss-security] 20231229 Re: Re: New SMTP smuggling attack
- [oss-security] 20231230 Re: Re: New SMTP smuggling attack
- [oss-security] 20231230 Re: Re: New SMTP smuggling attack
Sources
- CVE-2023-51765 · CVE Program
- CVE-2023-51765 · NVD
- FIRST EPSS
- GHSA-5rcq-25vc-g8qr · GitHub Advisory Database · CC BY 4.0
- CVE-2023-51765 · Red Hat security data · CC BY 4.0
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences