CVE-2023-51766: Exim: SMTP smuggling
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.
Other sources
Source: exim4 Version: 4.97-2 Severity: important Tags: security upstream Forwarded: https://bugs.exim.org/showbug.cgi?id=3063 X-Debbugs-Cc: carnil, Debian Security Team <team.org>
Hi,
The following vulnerability was published for exim4.
CVE-2023-51766[0]: | Exim through 4.97 allows SMTP smuggling in certain configurations. | Remote attackers can use a published exploitation technique to | inject e-mail messages that appear to originate from the Exim | server, allowing bypass of an SPF protection mechanism. This occurs | because Exim supports <LF>.<CR><LF> but some other popular e-mail | servers do not.
If you fix the vulnerability please also make sure to include the CVE (Common Vulnerabilities & Exposures) id in your changelog entry.
For further information see:
[0] https://security-tracker.debian.org/tracker/CVE-2023-51766 https://www.cve.org/CVERecord?id=CVE-2023-51766 [1] https://bugs.exim.org/showbug.cgi?id=3063
— Red Hat
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
ubuntu/exim4to a version that resolves this vulnerability.Fixed in 4.90.1-1ubuntu1.10+ - Upgrade
Upgrade
ubuntu/exim4to a version that resolves this vulnerability.Fixed in 4.93-13ubuntu1.10 - Upgrade
Upgrade
ubuntu/exim4to a version that resolves this vulnerability.Fixed in 4.95-4ubuntu2.5 - Upgrade
Upgrade
ubuntu/exim4to a version that resolves this vulnerability.Fixed in 4.96-17ubuntu2.2 - Upgrade
Upgrade
ubuntu/exim4to a version that resolves this vulnerability.Fixed in 4.97-3 - Upgrade
Upgrade
ubuntu/exim4to a version that resolves this vulnerability.Fixed in 4.86.2-2ubuntu2.6+ - Upgrade
Upgrade
debian/exim4to a version that resolves this vulnerability.Fixed in 4.94.2-7+deb11u3Fixed in 4.94.2-7+deb11u4Fixed in 4.96-15+deb12u7Fixed in 4.98.2-1Fixed in 4.99-4 - Upgrade
Upgrade
exim4to a version that resolves this vulnerability.Fixed in 4.97.1 - Compensating control
As a mitigation until Exim is upgraded, restrict SMTP access so only trusted hosts can submit mail (e.g., block external access to Exim’s SMTP port at the network/firewall/ACL level).
Event History
Frequently Asked Questions
What is the severity of CVE-2023-51766?
CVE-2023-51766 is considered a high severity vulnerability due to its potential to allow remote attackers to bypass SPF mechanisms.
How do I fix CVE-2023-51766?
To fix CVE-2023-51766, upgrade Exim to version 4.97.1 or later.
Which versions of Exim are affected by CVE-2023-51766?
CVE-2023-51766 affects Exim versions prior to 4.97.1 across multiple operating systems including various Ubuntu and Debian releases.
Can CVE-2023-51766 allow unauthorized email sending?
Yes, CVE-2023-51766 can allow unauthorized email sending by enabling spoofed MAIL FROM addresses.
What mitigation measures can be taken against CVE-2023-51766?
In addition to upgrading Exim, implementing strict email validation and monitoring SMTP traffic can help mitigate CVE-2023-51766.