CVE-2003-0540: The address parser code in Postfix 1.1.12 and earlier allows remote attackers to cause a denial of service (lo

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MEDIUM 5.0WATCHLISTDOWNGRADEMITIGATE

CVE-2003-0540 is a medium-severity flaw (CVSS 5.0) affecting postfix, linux. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

The address parser code in Postfix 1.1.12 and earlier allows remote attackers to cause a denial of service (lock) via (1) a malformed envelope address to a local host that would generate a bounce and contains the ".!" string in the MAIL FROM or Errors-To headers, which causes nqmgr to lock up, or (2) via a valid MAIL FROM with a RCPT TO containing a ".!" string, which causes an instance of the SMTP listener to lock up.

Why this priority

EPSS top 2%: very likely to be exploited
Public exploit reference
On your watchlist

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

Risk facts

CVSS score	5.0 (Medium)
EPSS exploit chance	21.3% (top 2%)
CISA exploited list	No
Published	2003-08-27
Last modified	2026-06-16

Publisher (CNA): MITRE · Vendor: conectiva · wietse venema

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

Am I affected?

Timeline

2003-08-27 04:00 UTCPublished CVE record published
2026-06-16 22:02 UTCUpdated Record last modified

wietse venema postfix DOWNGRADE

Affected: 1.0.21 · 1.1.11 · 1.1.12 · 1999-09-06 · 1999-12-31 · 2000-02-28 · 2001-11-15

Fixed in: no fixed release known

Safe to downgrade to: a release before 1.0.21

1. Check installed version

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

2. No fixed release: DOWNGRADE to a release before 1.0.21 (Debian / Ubuntu)

apt-cache madison postfix sudo apt install postfix=<VERSION_BEFORE_1.0.21> sudo apt-mark hold postfix

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

dnf --showduplicates list postfix sudo dnf downgrade postfix-<VERSION_BEFORE_1.0.21> 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.

conectiva linux MITIGATE

Affected: 7.0 · 8.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 7.0

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.

Public exploits and detection

Public code exists for this CVE. Treat unpatched systems as at risk, and only run PoCs in a lab.

Exploit-DB: Postfix 1.1.x - Denial of Service (1)
Exploit-DB: Postfix 1.1.x - Denial of Service (2)

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-2003-0540?

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

Is CVE-2003-0540 being exploited?

CVE-2003-0540 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-2003-0540 affect?

CVE-2003-0540 affects postfix, linux. Severity is medium (CVSS 5.0). The address parser code in Postfix 1.1.12 and earlier allows remote attackers to cause a denial of service (lock) via (1) a malformed envelope address to a local host that would generate a bounce and contains the ".!" string in the MAIL FRO

How urgent is CVE-2003-0540?

Priority 52/100. EPSS top 2%: very likely to be exploited; Public exploit reference; On your watchlist

Software pages

Postfix vulnerabilities

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References

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