# CVE-2023-51766: exim4: Exim before 4.97.1 allows SMTP smuggling in certain PIPELINING/CHUNKING configurations

CVE-2023-51766 is fixed in 6 products on 1 platform, first by exim4 4.90.1-1ubuntu1.10+esm3, released December 23, 2023. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2023-51766
- Priority: Routine
- CVSS: 5.3 (medium)
- EPSS: 0.0110
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Dec 23, 2023

## 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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | exim4 Debian 11.6 (bullseye) | 4.94.2-7+deb11u2 | [DSA-5597-1](https://patchblox.com/security/data/fix/linux/dsa-5597-1.md) | Jan 4, 2024 |
| Linux | exim4 Debian 12.15 (bookworm) | 4.96-15+deb12u4 | [DSA-5597-1](https://patchblox.com/security/data/fix/linux/dsa-5597-1.md) | Jan 4, 2024 |
| Linux | exim4 Debian 13.5 (trixie) | 4.97-3 | [DEBIAN-CVE-2023-51766](https://patchblox.com/security/data/fix/linux/debian-cve-2023-51766.md) | Dec 24, 2023 |
| Linux | exim4 Debian 14 | 4.97-3 | [DEBIAN-CVE-2023-51766](https://patchblox.com/security/data/fix/linux/debian-cve-2023-51766.md) | Dec 24, 2023 |
| Linux | exim4 Ubuntu 18.04.6 LTS (bionic) | 4.90.1-1ubuntu1.10+esm3 | [exim4 4.90.1-1ubuntu1.10+esm3](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-exim4-4.90.1-1ubuntu1.10-esm3.md) | Dec 23, 2023 |
| Linux | exim4 Ubuntu 20.04 LTS (focal) | 4.93-13ubuntu1.10 | [exim4 4.93-13ubuntu1.10](https://patchblox.com/security/data/fix/linux/ubuntu-focal-exim4-4.93-13ubuntu1.10.md) | Dec 23, 2023 |
| Linux | exim4 Ubuntu 22.04.1 LTS (jammy) | 4.95-4ubuntu2.5 | [exim4 4.95-4ubuntu2.5](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-exim4-4.95-4ubuntu2.5.md) | Dec 23, 2023 |
| Linux | exim4 Ubuntu 24.10 (oracular) | 4.97-3 | [exim4 4.97-3](https://patchblox.com/security/data/fix/linux/ubuntu-oracular-exim4-4.97-3.md) | Jan 16, 2026 |
| Linux | exim4 Ubuntu 25.04 (plucky) | 4.97-3 | [exim4 4.97-3](https://patchblox.com/security/data/fix/linux/ubuntu-plucky-exim4-4.97-3.md) | Jan 16, 2026 |
| Linux | exim4-base Ubuntu 18.04.6 LTS (bionic) | 4.90.1-1ubuntu1.10+esm3 | [exim4-base 4.90.1-1ubuntu1.10+esm3](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-exim4-base-4.90.1-1ubuntu1.10-esm3.md) | Dec 23, 2023 |
| Linux | exim4-base Ubuntu 20.04 LTS (focal) | 4.93-13ubuntu1.10 | [exim4-base 4.93-13ubuntu1.10](https://patchblox.com/security/data/fix/linux/ubuntu-focal-exim4-base-4.93-13ubuntu1.10.md) | Dec 23, 2023 |
| Linux | exim4-base Ubuntu 22.04.1 LTS (jammy) | 4.95-4ubuntu2.5 | [exim4-base 4.95-4ubuntu2.5](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-exim4-base-4.95-4ubuntu2.5.md) | Dec 23, 2023 |
| Linux | exim4-base Ubuntu 24.10 (oracular) | 4.97-3 | [exim4-base 4.97-3](https://patchblox.com/security/data/fix/linux/ubuntu-oracular-exim4-base-4.97-3.md) | Jan 16, 2026 |
| Linux | exim4-base Ubuntu 25.04 (plucky) | 4.97-3 | [exim4-base 4.97-3](https://patchblox.com/security/data/fix/linux/ubuntu-plucky-exim4-base-4.97-3.md) | Jan 16, 2026 |
| Linux | exim4-config Ubuntu 18.04.6 LTS (bionic) | 4.90.1-1ubuntu1.10+esm3 | [exim4-config 4.90.1-1ubuntu1.10+esm3](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-exim4-config-4.90.1-1ubuntu1.10-esm3.md) | Dec 23, 2023 |
| Linux | exim4-config Ubuntu 20.04 LTS (focal) | 4.93-13ubuntu1.10 | [exim4-config 4.93-13ubuntu1.10](https://patchblox.com/security/data/fix/linux/ubuntu-focal-exim4-config-4.93-13ubuntu1.10.md) | Dec 23, 2023 |
| Linux | exim4-config Ubuntu 22.04.1 LTS (jammy) | 4.95-4ubuntu2.5 | [exim4-config 4.95-4ubuntu2.5](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-exim4-config-4.95-4ubuntu2.5.md) | Dec 23, 2023 |
| Linux | exim4-config Ubuntu 24.10 (oracular) | 4.97-3 | [exim4-config 4.97-3](https://patchblox.com/security/data/fix/linux/ubuntu-oracular-exim4-config-4.97-3.md) | Jan 16, 2026 |
| Linux | exim4-config Ubuntu 25.04 (plucky) | 4.97-3 | [exim4-config 4.97-3](https://patchblox.com/security/data/fix/linux/ubuntu-plucky-exim4-config-4.97-3.md) | Jan 16, 2026 |
| Linux | exim4-daemon-heavy Ubuntu 18.04.6 LTS (bionic) | 4.90.1-1ubuntu1.10+esm3 | [exim4-daemon-heavy 4.90.1-1ubuntu1.10+esm3](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-exim4-daemon-heavy-4.90.1-1ubuntu1.10-esm3.md) | Dec 23, 2023 |
| Linux | exim4-daemon-heavy Ubuntu 20.04 LTS (focal) | 4.93-13ubuntu1.10 | [exim4-daemon-heavy 4.93-13ubuntu1.10](https://patchblox.com/security/data/fix/linux/ubuntu-focal-exim4-daemon-heavy-4.93-13ubuntu1.10.md) | Dec 23, 2023 |
| Linux | exim4-daemon-heavy Ubuntu 22.04.1 LTS (jammy) | 4.95-4ubuntu2.5 | [exim4-daemon-heavy 4.95-4ubuntu2.5](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-exim4-daemon-heavy-4.95-4ubuntu2.5.md) | Dec 23, 2023 |
| Linux | exim4-daemon-heavy Ubuntu 24.10 (oracular) | 4.97-3 | [exim4-daemon-heavy 4.97-3](https://patchblox.com/security/data/fix/linux/ubuntu-oracular-exim4-daemon-heavy-4.97-3.md) | Jan 16, 2026 |
| Linux | exim4-daemon-heavy Ubuntu 25.04 (plucky) | 4.97-3 | [exim4-daemon-heavy 4.97-3](https://patchblox.com/security/data/fix/linux/ubuntu-plucky-exim4-daemon-heavy-4.97-3.md) | Jan 16, 2026 |
| Linux | exim4-daemon-light Ubuntu 18.04.6 LTS (bionic) | 4.90.1-1ubuntu1.10+esm3 | [exim4-daemon-light 4.90.1-1ubuntu1.10+esm3](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-exim4-daemon-light-4.90.1-1ubuntu1.10-esm3.md) | Dec 23, 2023 |
| Linux | exim4-daemon-light Ubuntu 20.04 LTS (focal) | 4.93-13ubuntu1.10 | [exim4-daemon-light 4.93-13ubuntu1.10](https://patchblox.com/security/data/fix/linux/ubuntu-focal-exim4-daemon-light-4.93-13ubuntu1.10.md) | Dec 23, 2023 |
| Linux | exim4-daemon-light Ubuntu 22.04.1 LTS (jammy) | 4.95-4ubuntu2.5 | [exim4-daemon-light 4.95-4ubuntu2.5](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-exim4-daemon-light-4.95-4ubuntu2.5.md) | Dec 23, 2023 |
| Linux | exim4-daemon-light Ubuntu 24.10 (oracular) | 4.97-3 | [exim4-daemon-light 4.97-3](https://patchblox.com/security/data/fix/linux/ubuntu-oracular-exim4-daemon-light-4.97-3.md) | Jan 16, 2026 |
| Linux | exim4-daemon-light Ubuntu 25.04 (plucky) | 4.97-3 | [exim4-daemon-light 4.97-3](https://patchblox.com/security/data/fix/linux/ubuntu-plucky-exim4-daemon-light-4.97-3.md) | Jan 16, 2026 |
| Linux | eximon4 Ubuntu 18.04.6 LTS (bionic) | 4.90.1-1ubuntu1.10+esm3 | [eximon4 4.90.1-1ubuntu1.10+esm3](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-eximon4-4.90.1-1ubuntu1.10-esm3.md) | Dec 23, 2023 |
| Linux | eximon4 Ubuntu 20.04 LTS (focal) | 4.93-13ubuntu1.10 | [eximon4 4.93-13ubuntu1.10](https://patchblox.com/security/data/fix/linux/ubuntu-focal-eximon4-4.93-13ubuntu1.10.md) | Dec 23, 2023 |
| Linux | eximon4 Ubuntu 22.04.1 LTS (jammy) | 4.95-4ubuntu2.5 | [eximon4 4.95-4ubuntu2.5](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-eximon4-4.95-4ubuntu2.5.md) | Dec 23, 2023 |
| Linux | eximon4 Ubuntu 24.10 (oracular) | 4.97-3 | [eximon4 4.97-3](https://patchblox.com/security/data/fix/linux/ubuntu-oracular-eximon4-4.97-3.md) | Jan 16, 2026 |
| Linux | eximon4 Ubuntu 25.04 (plucky) | 4.97-3 | [eximon4 4.97-3](https://patchblox.com/security/data/fix/linux/ubuntu-plucky-eximon4-4.97-3.md) | Jan 16, 2026 |

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Data as of 2026-11-09T07:25:28Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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