CVE-2011-1720: The SMTP server in Postfix before 2.5.13, 2.6.x before 2.6.10, 2.7.x before 2.7.4, and 2.8.x before 2.8.3, whe

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MEDIUM 6.8DOWNGRADE

CVE-2011-1720 is a medium-severity flaw (CVSS 6.8) affecting postfix. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

The SMTP server in Postfix before 2.5.13, 2.6.x before 2.6.10, 2.7.x before 2.7.4, and 2.8.x before 2.8.3, when certain Cyrus SASL authentication methods are enabled, does not create a new server handle after client authentication fails, which allows remote attackers to cause a denial of service (heap memory corruption and daemon crash) or possibly execute arbitrary code via an invalid AUTH command with one method followed by an AUTH command with

Why this priority

EPSS top 2%: very likely to be exploited

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

Risk facts

CVSS score	6.8 (Medium)
EPSS exploit chance	21.5% (top 2%)
CISA exploited list	No
Weakness	CWE-119
Published	2011-05-13
Last modified	2026-06-16

Publisher (CNA): MITRE · Vendor: postfix

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

Am I affected?

Timeline

2011-05-13 17:05 UTCPublished CVE record published
2026-06-16 23:29 UTCUpdated Record last modified

postfix postfix DOWNGRADE

Affected: 2.0.0 · 2.0.1 · 2.0.2 · 2.0.3 · 2.0.4 · 2.0.5 · 2.0.6 · 2.0.7

Fixed in: no fixed release known

Safe to downgrade to: a release before 2.0.0

1. Check installed version

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

2. No fixed release: DOWNGRADE to a release before 2.0.0 (Debian / Ubuntu)

apt-cache madison postfix sudo apt install postfix=<VERSION_BEFORE_2.0.0> sudo apt-mark hold postfix

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

dnf --showduplicates list postfix sudo dnf downgrade postfix-<VERSION_BEFORE_2.0.0> 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.

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-2011-1720?

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

Is CVE-2011-1720 being exploited?

CVE-2011-1720 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-2011-1720 affect?

CVE-2011-1720 affects postfix. Severity is medium (CVSS 6.8). The SMTP server in Postfix before 2.5.13, 2.6.x before 2.6.10, 2.7.x before 2.7.4, and 2.8.x before 2.8.3, when certain Cyrus SASL authentication methods are enabled, does not create a new server handle after client authentication fails, wh

How urgent is CVE-2011-1720?

Priority 48/100. EPSS top 2%: very likely to be exploited

Software pages

Postfix vulnerabilities

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References

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