Description
OpenSMTPD before 6.6.4 allows remote code execution because of an out-of-bounds read in mta_io in mta_session.c for multi-line replies. Although this vulnerability affects the client side of OpenSMTPD, it is possible to attack a server because the server code launches the client code during bounce handling.
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 | opensmtpd | 6.6.4p1-1 | — |
| Debian 13 | opensmtpd | 6.6.4p1-1 | — |
| Debian 12 | opensmtpd | 6.6.4p1-1 | — |
| Debian 10 | opensmtpd | 6.0.3p1-5+deb10u4 | DSA-4634-1 |
| Debian 9 | opensmtpd | 6.0.2p1-2+deb9u3 | DSA-4634-1 |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 20.04 LTS | opensmtpd | 6.6.4p1-1 | — |
| Ubuntu 18.04 LTS | opensmtpd | 6.0.3p1-1ubuntu0.2 | USN-4294-1 |
Show 2 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu Pro 16.04 LTS | opensmtpd | 5.7.3p2-1ubuntu0.1~esm2 | USN-4875-1 |
| Ubuntu Pro 14.04 LTS | opensmtpd | 5.4.1p1-1ubuntu0.1~esm1 | USN-4875-1 |
Alpine
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine v3.20 | opensmtpd-extras | 6.6.4-r0 | — |
| Alpine v3.19 | opensmtpd-extras | 6.6.4-r0 | — |
| Alpine v3.18 | opensmtpd-extras | 6.6.4-r0 | — |
| Alpine v3.17 | opensmtpd-extras | 6.6.4-r0 | — |
| Alpine v3.16 | opensmtpd-extras | 6.6.4-r0 | — |
Show 3 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine v3.15 | opensmtpd-extras | 6.6.4-r0 | — |
| Alpine v3.14 | opensmtpd-extras | 6.6.4-r0 | — |
| Alpine v3.13 | opensmtpd-extras | 6.6.4-r0 | — |
Public exploits
Exploit or proof-of-concept code for this vulnerability is publicly available, which lowers the bar for attackers. Treat it as a reason to patch sooner.
Metasploit 1 module
-
OpenSMTPD OOB Read Local Privilege Escalation
exploit/unix/local/opensmtpd_oob_read_lpe
Exploit-DB 2
- OpenSMTPD - OOB Read Local Privilege Escalation (Metasploit) EDB-48185 · local · Mar 9, 2020 · verified
- OpenSMTPD < 6.6.3p1 - Local Privilege Escalation + Remote Code Execution EDB-48140 · remote · Feb 26, 2020
Sources: PoC-in-GitHub, Metasploit Framework, Exploit-DB — updated daily. Only links are listed; no exploit code is hosted here.
Advisories 3
- USN-4875-1 opensmtpd vulnerabilities Ubuntu Security Notices (USN) · Jun 29, 2026
- USN-4294-1 OpenSMTPD vulnerabilities Ubuntu Security Notices (USN) · Apr 27, 2026
- DSA-4634-1 opensmtpd - security update Debian Security (DSA / DLA) · Mar 9, 2026
References
- https://www.openbsd.org/security.html
- https://www.openwall.com/lists/oss-security/2020/02/24/5
- [oss-security] 20200226 Re: LPE and RCE in OpenSMTPD's default install (CVE-2020-8794) mailing-list
- DSA-4634 vendor-advisory
- 20200227 LPE and RCE in OpenSMTPD's default install (CVE-2020-8794) mailing-list
- [oss-security] 20200301 Re: LPE and RCE in OpenSMTPD's default install (CVE-2020-8794) mailing-list
- [oss-security] 20200301 Re: LPE and RCE in OpenSMTPD's default install (CVE-2020-8794) mailing-list
- http://packetstormsecurity.com/files/156633/OpenSMTPD-Out-Of-Bounds-Read-Local-Privilege-Escalation.html
- FEDORA-2020-b92d7083ca vendor-advisory
- USN-4294-1 vendor-advisory
- [oss-security] 20210504 21Nails: Multiple vulnerabilities in Exim mailing-list