Exim before 4.97.1 allows SMTP smuggling in certain PIPELINING/CHUNKING configurations.
Priority LOW 26CWE-345Published · Updated
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
- No fix listed
Attack profile from CVSS 3.1 · NVD. Fix status from CNA. Impact type from CWE-345.
Summary
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.
Why it matters now
EPSS 0.01102 65th percentileScored 2026-11-07
Public exploit Yes 1 exploit referenceTagged by NVD
Fix No fix listed No fixed version in the sources yet
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 · 7
| CPE | Versions | Role | Vendor |
|---|---|---|---|
| cpe:2.3:a:exim:exim:*:*:*:*:*:*:*:* | before 4.97.1 | Vulnerable | Exim |
| cpe:2.3:a:fedoraproject:extra_packages_for_enterprise_linux:7.0:*:*:*:*:*:*:* | 7.0 | Vulnerable | Fedoraproject |
| cpe:2.3:a:fedoraproject:extra_packages_for_enterprise_linux:8.0:*:*:*:*:*:*:* | 8.0 | Vulnerable | Fedoraproject |
| cpe:2.3:a:fedoraproject:extra_packages_for_enterprise_linux:9.0:*:*:*:*:*:*:* | 9.0 | Vulnerable | Fedoraproject |
| cpe:2.3:o:fedoraproject:fedora:38:*:*:*:*:*:*:* | 38 | Vulnerable | Fedoraproject |
| cpe:2.3:o:fedoraproject:fedora:39:*:*:*:*:*:*:* | 39 | Vulnerable | Fedoraproject |
| cpe:2.3:o:debian:debian_linux:10.0:*:*:*:*:*:*:* | 10.0 | Vulnerable | Debian |
- cpe:2.3:a:exim:exim:*:*:*:*:*:*:*:* Versions before 4.97.1 Vulnerable ·Exim
- cpe:2.3:a:fedoraproject:extra_packages_for_enterprise_linux:7.0:*:*:*:*:*:*:* Versions 7.0 Vulnerable ·Fedoraproject
- cpe:2.3:a:fedoraproject:extra_packages_for_enterprise_linux:8.0:*:*:*:*:*:*:* Versions 8.0 Vulnerable ·Fedoraproject
- cpe:2.3:a:fedoraproject:extra_packages_for_enterprise_linux:9.0:*:*:*:*:*:*:* Versions 9.0 Vulnerable ·Fedoraproject
- cpe:2.3:o:fedoraproject:fedora:38:*:*:*:*:*:*:* Versions 38 Vulnerable ·Fedoraproject
- cpe:2.3:o:fedoraproject:fedora:39:*:*:*:*:*:*:* Versions 39 Vulnerable ·Fedoraproject
- cpe:2.3:o:debian:debian_linux:10.0:*:*:*:*:*:*:* Versions 10.0 Vulnerable ·Debian
Remediation
No fixed version listed by the sources yet.
Vendor assessments
Timeline
- 2026-10-02 Threatist record created from CVE-2023-51766
- 2026-10-03 Alias added: GHSA-w6ww-869j-cgm6
References
Patch 2
Advisory 15
- https://sec-consult.com/blog/detail/smtp-smuggling-spoofing-e-mails-worldwide/
- https://bugs.exim.org/show_bug.cgi?id=3063
- https://www.openwall.com/lists/oss-security/2023/12/23/2
- [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=2255852
- [oss-security] 20231229 CVE-2023-51766: Exim: SMTP smuggling
- https://github.com/Exim/exim/blob/master/doc/doc-txt/cve-2023-51766
- [oss-security] 20240101 Re: CVE-2023-51766: Exim: SMTP smuggling
- [oss-security] 20240101 Re: CVE-2023-51766: Exim: SMTP smuggling
- [oss-security] 20240101 Re: CVE-2023-51766: Exim: SMTP smuggling
- [debian-lts-announce] 20240105 [SECURITY] [DLA 3708-1] exim4 security update
- FEDORA-2024-1ef6197a49
- FEDORA-2024-e0841c83bb
- https://lwn.net/Articles/956533/
Sources
- CVE-2023-51766 · CVE Program
- CVE-2023-51766 · NVD
- FIRST EPSS
- GHSA-w6ww-869j-cgm6 · GitHub Advisory Database · CC BY 4.0
- CVE-2023-51766 · 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