CVE-2020-8794
CriticalPublic exploitOpenSMTPD 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.
Published Feb 25, 2020 · Updated Aug 5, 2026 · Also known as DEBIAN-CVE-2020-8794, DSA-4634-1, UBUNTU-CVE-2020-8794
Key Facts
Patch immediately- CVE-2020-8794 is a critical-severity vulnerability (CVSS 9.8 v3.1) affecting Opensmtpd, Ubuntu Linux (Canonical), Debian Linux and 2 more products.
- It is not listed in any known-exploited vulnerabilities catalog. Public exploit code is available.
- EPSS estimates a 89% probability of exploitation in the next 30 days.
- Fixed versions are available, including Opensmtpd 5.4.1p1-1ubuntu0.1~esm1, Opensmtpd 5.7.3p2-1ubuntu0.1~esm2, Opensmtpd 6.0.2p1-2+deb9u3.
- Brandefense priority: patch immediately, because it is very likely to be exploited soon.
CVSS v3.1
9.8
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
EPSS (30-day exploit likelihood)
89%
Higher than 99.7% of all scored CVEs
Exploited in the wild
No known
Not in a known-exploited catalog
Public exploit code
Available
Proof-of-concept or weaponized module
Get the full CVE-2020-8794 brief as a PDF
Every affected product and fixed release, exploitation status and a first 24 hours response checklist, emailed within minutes.
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.
Affected Products
33 affected entries in total| Product | Affected versions | Fixed in |
|---|---|---|
| OpensmtpdOpensmtpd | See advisory | 6.6.4 |
| Ubuntu LinuxCanonical | 18.04, 19.10 | n/a |
| Debian LinuxDebian | 10.0, 9.0 | n/a |
| FedoraFedoraproject | 31, 32 | n/a |
| opensmtpd-extrasalpine | See advisory | 6.6.4-r0 |
Patched Releases
Opensmtpd
5.4.1p1-1ubuntu0.1~esm1, 5.7.3p2-1ubuntu0.1~esm2, 6.0.2p1-2+deb9u3, 6.0.3p1-1ubuntu0.2, 6.0.3p1-5+deb10u4, 6.6.4p1-1, 6.6.4
opensmtpd-extras
6.6.4-r0
Timeline
Publicly disclosed
Feb 25, 2020
Last updated
Aug 5, 2026
Weakness Type
- CWE-125 Out-of-bounds Read
References
- advisory20200227 LPE and RCE in OpenSMTPD's default install (CVE-2020-8794)
- advisoryhttps://security-tracker.debian.org/tracker/CVE-2020-8794
- advisoryhttps://ubuntu.com/security/CVE-2020-7247
- advisoryhttps://ubuntu.com/security/CVE-2020-8793
- advisoryhttps://ubuntu.com/security/CVE-2020-8794
FAQ
Common Questions.
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.
Affected: Opensmtpd; Ubuntu Linux (Canonical) versions 18.04, 19.10; Debian Linux versions 10.0, 9.0, among others. The full list is in the CVE brief.
It is not listed in any known-exploited vulnerabilities catalog.
No, it is not currently listed in the CISA Known Exploited Vulnerabilities catalog.
Public exploit code is available.
Fixed versions are available, including Opensmtpd 5.4.1p1-1ubuntu0.1~esm1, Opensmtpd 5.7.3p2-1ubuntu0.1~esm2, Opensmtpd 6.0.2p1-2+deb9u3.
Brandefense priority: patch immediately, because it is very likely to be exploited soon.
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