CVE-2026-43964: Postfix before 3.8.16, 3.9 before 3.9.10, and 3.10 before 3.10.9 sometimes allows a buffer over-read and proce

Routine

LOW 3.7REMOTEUPGRADE

CVE-2026-43964 is a low-severity flaw (CVSS 3.7) affecting postfix. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Postfix before 3.8.16, 3.9 before 3.9.10, and 3.10 before 3.10.9 sometimes allows a buffer over-read and process crash via an enhanced status code that lacks text after the third number.

Why this priority

Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	3.7 (Low)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	None
User interaction	None
EPSS exploit chance	0.5% (top 57%)
CISA exploited list	No
Weakness	CWE-193
Published	2026-05-04
Last modified	2026-08-20

Publisher (CNA): MITRE · Vendor: postfix

Last updated 2026-08-20 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-05-04 19:16 UTCPublished CVE record published
2026-08-20 13:18 UTCUpdated Record last modified

postfix postfix UPGRADE

Affected: < 3.8.16 · >= 3.9.0 and < 3.9.10 · >= 3.10.0 and < 3.10.9

Fixed in: 3.8.16, 3.9.10, 3.10.9

Safe to downgrade to: a release before 3.9.0

1. Check installed version

apt-cache policy postfix || rpm -q postfix || postfix --version

2. UPGRADE to 3.8.16 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade postfix

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade postfix

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 3.9.0 (Debian / Ubuntu)

apt-cache madison postfix sudo apt install postfix=<VERSION_BEFORE_3.9.0> sudo apt-mark hold postfix

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list postfix sudo dnf downgrade postfix-<VERSION_BEFORE_3.9.0> sudo dnf versionlock add postfix

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Advisories and coverage

Official advisories

AlmaLinux Errata: [ALSA-2026:26205] Important: postfix security update 2026-06-17

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-43964?

postfix: upgrade to 3.8.16, 3.9.10, 3.10.9. Exact commands for each OS are on this page.

Is CVE-2026-43964 being exploited?

CVE-2026-43964 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-43964 affect?

CVE-2026-43964 affects postfix. Severity is low (CVSS 3.7). Postfix before 3.8.16, 3.9 before 3.9.10, and 3.10 before 3.10.9 sometimes allows a buffer over-read and process crash via an enhanced status code that lacks text after the third number.

How urgent is CVE-2026-43964?

Priority 29/100. Remotely exploitable, no login, no user action

Software pages

Postfix vulnerabilities

References

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