🛡️ CVE-2023-51766 — debian-linux
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.
How this vulnerability can be exploited
This issue can be reached over the network, attack complexity is low, an attacker needs no privileges on the target. No user interaction is required. The scope is unchanged, so the impact stays within the vulnerable component. Rated impact: confidentiality none, integrity low, availability none.
CVSS metrics in full
The score comes from this vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
- Attack vector: Network — reachable from anywhere that can route to the service.
- Attack complexity: Low — the attack works reliably, with no preparation.
- Privileges required: None — an unauthenticated stranger can try it.
- User interaction: None — nobody has to be tricked into anything.
- Scope: Unchanged — the damage stays inside the vulnerable component.
- Confidentiality impact: None.
- Integrity impact: Low — limited, and the attacker does not choose what is affected.
- Availability impact: None.
Weakness class
CVE-2023-51766 is classified as CWE-345: Insufficient Verification of Data Authenticity. Data is trusted without confirming it really came from the claimed source and was not altered.
Affected software
CVE-2023-51766 is recorded against 4 packages.
- debian-linux
- exim (fixed in 4.97.1)
- extra-packages-for-enterprise-linux
- fedora
Timeline and source
Published on 24 December 2023 and last revised on 17 June 2026. A public exploit is known to exist, which raises the urgency of patching considerably. A vendor advisory or fix has been published. Record sourced from NVD.
References
www.openwall.com
www.openwall.com
www.openwall.com
www.openwall.com
www.openwall.com
www.openwall.com
bugs.exim.org
bugzilla.redhat.com
exim.org
fahrplan.events.ccc.de
git.exim.org
git.exim.org
github.com
lists.debian.org
lists.fedoraproject.org
lists.fedoraproject.org
lwn.net
sec-consult.com
www.openwall.com
www.youtube.com
www.openwall.com
www.openwall.com
www.openwall.com
www.openwall.com
www.openwall.com
www.openwall.com
bugs.exim.org
bugzilla.redhat.com
exim.org
fahrplan.events.ccc.de
git.exim.org
git.exim.org
github.com
lists.debian.org
lists.fedoraproject.org
lists.fedoraproject.org
lists.fedoraproject.org
lists.fedoraproject.org
lwn.net
sec-consult.com
Other advisories for this package
debian-linux has other advisories on record. If you are patching this one, these are worth checking on the same host:
- CVE-2026-12996 (8.1 High, published 30 Jul 2026)
- CVE-2026-14355 (5.6 Medium, published 3 Jul 2026)
- CVE-2026-56968 (3.7 Low, published 23 Jun 2026)
- CVE-2026-49975 (7.5 High, published 8 Jun 2026)
- CVE-2026-9256 (8.1 High, published 22 May 2026)
- CVE-2026-46333 (7.1 High, published 15 May 2026)
- CVE-2026-31431 (7.8 High, published 22 Apr 2026)
- CVE-2026-41082 (7.3 High, published 16 Apr 2026)
Same weakness in other software
These advisories are the same class of weakness (CWE-345: Insufficient Verification of Data Authenticity) in other software:
- CVE-2026-54764 (5.8 Medium, published 18 Aug 2026)
- CVE-2026-52737 (5.3 Medium, published 18 Aug 2026)
- CVE-2026-71576 (8.5 High, published 10 Aug 2026)
- CVE-2026-21078 (6.5 Medium, published 10 Aug 2026)
- CVE-2026-71965 (8.8 High, published 10 Aug 2026)
- CVE-2026-17011 (3.8 Low, published 9 Aug 2026)
- CVE-2026-15148 (5.3 Medium, published 7 Aug 2026)
- CVE-2026-15239 (5.3 Medium, published 7 Aug 2026)
CVE-2023-51766 on other distributions
Each distribution ships its own build and its own fixed version. Pick the one you run:
Details
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Affected Packages
| Software | From version | Fixed in |
|---|---|---|
| debian-linux | — | — |
| exim | — | 4.97.1 |
| extra-packages-for-enterprise-linux | — | — |
| fedora | — | — |
References
Similar Threats
- Critical CVE-2022-0194
- High CVE-2022-0367
- Medium CVE-2022-0171
- High CVE-2022-0135
- High CVE-2022-0204
Exploit Protection
Are you running debian-linux?
CVE-2023-51766 carries CVSS 5.3 Medium rating and a public exploit already exists. BotEraser checks your installation against this and other known CVE records, and blocks IPs associated with exploit activity.
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ⓘ Data Notice: The information presented above has been compiled from publicly available internet sources. Boteraser aggregates this data solely for informational purposes and does not independently classify, evaluate, or endorse any findings about the vulnerabilities listed. The accuracy and completeness of this information is the sole responsibility of the original publishers. Boteraser and its operators accept no liability for any decisions made based on this data.
