CVE-2011-2523: vsftpd 2.3.4 downloaded between 20110630 and 20110703 contains a backdoor which opens a shell on port 6200/tcp

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CRITICAL 9.8REMOTEWATCHLISTDOWNGRADEMITIGATE

CVE-2011-2523 is a critical-severity flaw (CVSS 9.8) affecting vsftpd, debian linux. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

vsftpd 2.3.4 downloaded between 20110630 and 20110703 contains a backdoor which opens a shell on port 6200/tcp.

Why this priority

Critical severity
EPSS top 1%: very likely to be exploited
Public exploit reference
Remotely exploitable, no login, no user action
On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	96.2% (top 1%)
CISA exploited list	No
Weakness	CWE-78
Published	2019-11-27
Last modified	2026-06-16

Publisher (CNA): Red Hat, Inc. · Vendor: debian · vsftpd project

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

Am I affected?

Timeline

2019-11-27 21:15 UTCPublished CVE record published
2026-06-16 23:31 UTCUpdated Record last modified

vsftpd project vsftpd DOWNGRADE

Affected: 2.3.4

Fixed in: no fixed release known

Safe to downgrade to: a release before 2.3.4

1. Check installed version

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

2. No fixed release: DOWNGRADE to a release before 2.3.4 (Debian / Ubuntu)

apt-cache madison vsftpd sudo apt install vsftpd=<VERSION_BEFORE_2.3.4> sudo apt-mark hold vsftpd

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

dnf --showduplicates list vsftpd sudo dnf downgrade vsftpd-<VERSION_BEFORE_2.3.4> sudo dnf versionlock add vsftpd

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.

debian debian linux MITIGATE

Affected: 8.0 · 9.0 · 10.0

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.

Exact fixes by distribution

A distro patch exists: prefer upgrading over downgrading.

Fedora 46 · keepalived · FIXED · 2.4.3-1.fc46 · FEDORA-2026-0c83a077d7 · source

sudo dnf upgrade --advisory=FEDORA-2026-0c83a077d7

Fedora ELN · dracut · FIXED · 111-5.eln159 · FEDORA-2026-982407d9e3 · source

sudo dnf upgrade --advisory=FEDORA-2026-982407d9e3

Debian 12 · vsftpd · NOT AFFECTED

Debian 13 · vsftpd · NOT AFFECTED

RHEL 5 · vsftpd · NOT AFFECTED

RHEL 6 · vsftpd · NOT AFFECTED

RHEL 7 · vsftpd · NOT AFFECTED

RHEL 8 · vsftpd · NOT AFFECTED

Public exploits and detection

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

GitHub PoC: padsalatushal/CVE-2011-2523 (15 stars)
GitHub PoC: Lynk4/CVE-2011-2523 (5 stars)
GitHub PoC: Maalfer/CVE-2011-2523-vsftpd-2.3.4-exploit (5 stars)
Write-up: packetstormsecurity.com/files/102745/VSFTPD-2.3.4-Backdoor-Command-Execution.html
Exploit-DB: vsftpd 2.3.4 - Backdoor Command Execution
Exploit-DB: vsftpd 2.3.4 - Backdoor Command Execution (Metasploit)
Metasploit: VSFTPD 2.3.4 Backdoor Command Execution
Nuclei scan template: VSFTPD 2.3.4 - Backdoor Command Execution

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-2011-2523?

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

Is CVE-2011-2523 being exploited?

CVE-2011-2523 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-2011-2523 affect?

CVE-2011-2523 affects vsftpd, debian linux. Severity is critical (CVSS 9.8). vsftpd 2.3.4 downloaded between 20110630 and 20110703 contains a backdoor which opens a shell on port 6200/tcp.

How urgent is CVE-2011-2523?

Priority 74/100. Critical severity; EPSS top 1%: very likely to be exploited; Public exploit reference; Remotely exploitable, no login, no user action; On your watchlist

Software pages

Debian vulnerabilities · vsftpd vulnerabilities

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References

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