CVE-2005-0337: Postfix 2.1.3, when /proc/net/if_inet6 is not available and permit_mx_backup is enabled in smtpd_recipient_res

This month

HIGH 7.5WATCHLISTDOWNGRADEMITIGATEMITIGATE

CVE-2005-0337 is a high-severity flaw (CVSS 7.5) affecting postfix, enterprise linux, enterprise linux desktop. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Postfix 2.1.3, when /proc/net/if_inet6 is not available and permit_mx_backup is enabled in smtpd_recipient_restrictions, allows remote attackers to bypass e-mail restrictions and perform mail relaying by sending mail to an IPv6 hostname.

Why this priority

High severity
On your watchlist

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	7.5 (High)
EPSS exploit chance	2.8% (top 14%)
CISA exploited list	No
Published	2005-05-02
Last modified	2026-06-16

Publisher (CNA): MITRE · Vendor: redhat · suse · wietse venema

Last updated 2026-06-16 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2005-05-02 04:00 UTCPublished CVE record published
2026-06-16 22:10 UTCUpdated Record last modified

wietse venema postfix DOWNGRADE

Affected: 2.1.3

Fixed in: no fixed release known

Safe to downgrade to: a release before 2.1.3

1. Check installed version

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

2. No fixed release: DOWNGRADE to a release before 2.1.3 (Debian / Ubuntu)

apt-cache madison postfix sudo apt install postfix=<VERSION_BEFORE_2.1.3> sudo apt-mark hold postfix

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list postfix sudo dnf downgrade postfix-<VERSION_BEFORE_2.1.3> 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.

redhat enterprise linux MITIGATE

Affected: 4.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 4.0

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

redhat enterprise linux desktop MITIGATE

Affected: 4.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 4.0

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

suse suse linux MITIGATE

Affected: 8.0 · 8.1 · 8.2 · 9.0 · 9.1 · 9.2

Fixed in: no fixed release known

Safe to downgrade to: a release before 8.0

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

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-2005-0337?

postfix: downgrade or apply the listed mitigation; enterprise linux: mitigate or apply the listed mitigation; enterprise linux desktop: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2005-0337 being exploited?

CVE-2005-0337 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-2005-0337 affect?

CVE-2005-0337 affects postfix, enterprise linux, enterprise linux desktop. Severity is high (CVSS 7.5). Postfix 2.1.3, when /proc/net/if_inet6 is not available and permit_mx_backup is enabled in smtpd_recipient_restrictions, allows remote attackers to bypass e-mail restrictions and perform mail relaying by sending mail to an IPv6 hostname.

How urgent is CVE-2005-0337?

Priority 53/100. High severity; On your watchlist

Software pages

Postfix vulnerabilities

Related CVEs

CVE-2023-51764 MEDIUM 5.3 UPGRADE MITIGATE Postfix through 3.8.5 allows SMTP smuggling unless configured with smtpd_data_restrictions=reject_unauth_pipel
CVE-2026-43964 LOW 3.7 UPGRADE 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
CVE-2020-12063 MEDIUM 5.3 DOWNGRADE A certain Postfix 2.10.1-7 package could allow an attacker to send an email from an arbitrary-looking sender v
CVE-2017-10140 HIGH 7.8 UPGRADE Postfix before 2.11.10, 3.0.x before 3.0.10, 3.1.x before 3.1.6, and 3.2.x before 3.2.2 might allow local user
CVE-2012-0811 MEDIUM 6.5 UPGRADE Multiple SQL injection vulnerabilities in Postfix Admin (aka postfixadmin) before 2.3.5 allow remote authentic

References

← Back to latest CVEs