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.
Fixed in Linux distributions
Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.
Debian
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian 14 | exim4 | 4.97-3 | — |
| Debian 13 | exim4 | 4.97-3 | — |
| Debian 12 | exim4 | 4.96-15+deb12u4 | DSA-5597-1 |
| Debian 11 | exim4 | 4.94.2-7+deb11u2 | DSA-5597-1 |
| Debian 10 | exim4 | 4.92-8+deb10u9 | DLA-3708-1 |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 22.04 LTS | exim4 | 4.95-4ubuntu2.5 | USN-6611-1 |
| Ubuntu 20.04 LTS | exim4 | 4.93-13ubuntu1.10 | USN-6611-1 |
Show 4 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu Pro 20.04 LTS | exim4 | 4.93-13ubuntu1.12+esm1 | USN-8382-1 |
| Ubuntu Pro 18.04 LTS | exim4 | 4.90.1-1ubuntu1.10+esm3 | USN-8382-1, USN-6611-1 |
| Ubuntu Pro 16.04 LTS | exim4 | 4.86.2-2ubuntu2.6+esm6 | USN-8382-1, USN-6611-1 |
| Ubuntu Pro 14.04 LTS | exim4 | 4.82-3ubuntu2.4+esm9 | USN-8382-1 |
SUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| SUSE Package Hub 15 SP5 | exim | 4.97.1-bp155.5.9.1 | openSUSE-SU-2024:0007-1 |
openSUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| openSUSE Tumbleweed | exim | 4.97.1-1.1 | openSUSE-SU-2024:13543-1 |
| openSUSE Leap 15.5 | exim | 4.97.1-bp155.5.9.1 | openSUSE-SU-2024:0007-1 |
Alpine
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine v3.24 | exim | 4.97.1-r0 | — |
| Alpine v3.23 | exim | 4.97.1-r0 | — |
| Alpine v3.22 | exim | 4.97.1-r0 | — |
| Alpine v3.21 | exim | 4.97.1-r0 | — |
| Alpine v3.20 | exim | 4.97.1-r0 | — |
Show 1 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine v3.19 | exim | 4.97.1-r0 | — |
Wolfi
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Wolfi rolling | exim | 4.97.1-r0 | — |
Advisories 8
- WID-SEC-2026-3076 Dovecot: Mehrere Schwachstellen BSI CERT-Bund (WID) · Nov 12, 2026
- USN-6611-1 exim4 vulnerability Ubuntu Security Notices (USN) · Jun 25, 2026
- USN-8382-1 exim4 vulnerabilities Ubuntu Security Notices (USN) · Jun 4, 2026
- DSA-5597-1 exim4 - security update Debian Security (DSA / DLA) · Mar 9, 2026
- DLA-3708-1 exim4 - security update Debian Security (DSA / DLA) · Mar 9, 2026
- openSUSE-SU-2024:13543-1 exim-4.97.1-1.1 on GA media SUSE / openSUSE Security Updates · Feb 4, 2026
- openSUSE-SU-2024:0007-1 Security update for exim SUSE / openSUSE Security Updates · Feb 4, 2026
- WID-SEC-2023-3206 SMTP Implementierungen: Schwachstelle ermöglicht Umgehen von Sicherheitsvorkehrungen BSI CERT-Bund (WID) · Nov 11, 2024
References
- https://sec-consult.com/blog/detail/smtp-smuggling-spoofing-e-mails-worldwide/
- https://exim.org/static/doc/security/CVE-2023-51766.txt
- 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 mailing-list
- [oss-security] 20231225 Re: Re: New SMTP smuggling attack mailing-list
- https://git.exim.org/exim.git/commit/5bb786d5ad568a88d50d15452aacc8404047e5ca
- https://git.exim.org/exim.git/commit/cf1376206284f2a4f11e32d931d4aade34c206c5
- https://bugzilla.redhat.com/show_bug.cgi?id=2255852
- https://fahrplan.events.ccc.de/congress/2023/fahrplan/events/11782.html
- [oss-security] 20231229 CVE-2023-51766: Exim: SMTP smuggling mailing-list
- https://github.com/Exim/exim/blob/master/doc/doc-txt/cve-2023-51766
- [oss-security] 20240101 Re: CVE-2023-51766: Exim: SMTP smuggling mailing-list
- [oss-security] 20240101 Re: CVE-2023-51766: Exim: SMTP smuggling mailing-list
- [oss-security] 20240101 Re: CVE-2023-51766: Exim: SMTP smuggling mailing-list
- https://www.youtube.com/watch?v=V8KPV96g1To
- [debian-lts-announce] 20240105 [SECURITY] [DLA 3708-1] exim4 security update mailing-list
- FEDORA-2024-1ef6197a49 vendor-advisory
- FEDORA-2024-e0841c83bb vendor-advisory
- https://lwn.net/Articles/956533/