CVE-2001-0554: Buffer overflow in BSD-based telnetd telnet daemon on various operating systems allows remote attackers to exe

This week

HIGH 10.0WATCHLISTDOWNGRADEDOWNGRADEDOWNGRADE

CVE-2001-0554 is a high-severity flaw (CVSS 10.0) affecting kerberos, kerberos 5, linux netkit. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Buffer overflow in BSD-based telnetd telnet daemon on various operating systems allows remote attackers to execute arbitrary commands via a set of options including AYT (Are You There), which is not properly handled by the telrcv function.

Why this priority

Critical severity
EPSS top 1%: very likely to be exploited
Public exploit reference
On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	10.0 (High)
EPSS exploit chance	38.7% (top 1%)
CISA exploited list	No
Weakness	CWE-120
Published	2001-08-14
Last modified	2026-06-16

Publisher (CNA): MITRE · Vendor: freebsd · ibm · mit · netkit · sgi

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

Am I affected?

Timeline

2001-08-14 04:00 UTCPublished CVE record published
2026-06-16 21:54 UTCUpdated Record last modified

mit kerberos DOWNGRADE

Affected: 1.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 1.0

1. Check installed version

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

2. No fixed release: DOWNGRADE to a release before 1.0 (Debian / Ubuntu)

apt-cache madison kerberos sudo apt install kerberos=<VERSION_BEFORE_1.0> sudo apt-mark hold kerberos

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

dnf --showduplicates list kerberos sudo dnf downgrade kerberos-<VERSION_BEFORE_1.0> sudo dnf versionlock add kerberos

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.

mit kerberos 5 DOWNGRADE

Affected: 1.1 · 1.1.1 · 1.2 · 1.2.1 · 1.2.2

Fixed in: no fixed release known

Safe to downgrade to: a release before 1.1

1. Check installed version

apt-cache policy kerberos-5 || rpm -q kerberos-5 || kerberos-5 --version

2. No fixed release: DOWNGRADE to a release before 1.1 (Debian / Ubuntu)

apt-cache madison kerberos-5 sudo apt install kerberos-5=<VERSION_BEFORE_1.1> sudo apt-mark hold kerberos-5

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

dnf --showduplicates list kerberos-5 sudo dnf downgrade kerberos-5-<VERSION_BEFORE_1.1> sudo dnf versionlock add kerberos-5

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.

netkit linux netkit DOWNGRADE

Affected: 0.10 · 0.11 · 0.12

Fixed in: no fixed release known

Safe to downgrade to: a release before 0.10

1. Check installed version

apt-cache policy linux-netkit || rpm -q linux-netkit || linux-netkit --version

2. No fixed release: DOWNGRADE to a release before 0.10 (Debian / Ubuntu)

apt-cache madison linux-netkit sudo apt install linux-netkit=<VERSION_BEFORE_0.10> sudo apt-mark hold linux-netkit

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

dnf --showduplicates list linux-netkit sudo dnf downgrade linux-netkit-<VERSION_BEFORE_0.10> sudo dnf versionlock add linux-netkit

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.

sgi irix MITIGATE

Affected: 6.5

Fixed in: no fixed release known

Safe to downgrade to: a release before 6.5

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.

freebsd freebsd MITIGATE

Affected: 2.0 · 2.0.1 · 2.0.5 · 2.1 stable · 2.1.0 · 2.1.5 · 2.1.6 · 2.1.6.1

Fixed in: no fixed release known

Safe to downgrade to: a release before 2.0

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.

ibm aix MITIGATE

Affected: 4.3 · 4.3.1 · 4.3.2 · 4.3.3 · 5.1

Fixed in: no fixed release known

Safe to downgrade to: a release before 4.3

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 · rust-cargo-semver-checks · FIXED · 0.51.0-7.fc46 · FEDORA-2026-1bbb7e855a · source

sudo dnf upgrade --advisory=FEDORA-2026-1bbb7e855a

Fedora ELN · fuse-sshfs · FIXED · 3.7.6-3.eln159 · FEDORA-2026-bcb7be7c5c · source

sudo dnf upgrade --advisory=FEDORA-2026-bcb7be7c5c

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: Solaris 2.x/7.0/8 / IRIX 6.5.x / OpenBSD 2.x / NetBSD 1.x / Debian 3 / HP-UX 10 - 'TelnetD' Remote Buffer Overflow

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-2001-0554?

kerberos: downgrade or apply the listed mitigation; kerberos 5: downgrade or apply the listed mitigation; linux netkit: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2001-0554 being exploited?

CVE-2001-0554 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-2001-0554 affect?

CVE-2001-0554 affects kerberos, kerberos 5, linux netkit. Severity is high (CVSS 10.0). Buffer overflow in BSD-based telnetd telnet daemon on various operating systems allows remote attackers to execute arbitrary commands via a set of options including AYT (Are You There), which is not properly handled by the telrcv function.

How urgent is CVE-2001-0554?

Priority 70/100. Critical severity; EPSS top 1%: very likely to be exploited; Public exploit reference; On your watchlist

Related CVEs

CVE-2020-13110 HIGH 7.8 UPGRADE The kerberos package before 1.0.0 for Node.js allows arbitrary code execution and privilege escalation via inj
CVE-2018-5710 MEDIUM 6.5 UPGRADE An issue was discovered in MIT Kerberos 5 (aka krb5) through 1.16
CVE-2018-5709 HIGH 7.5 UPGRADE An issue was discovered in MIT Kerberos 5 (aka krb5) through 1.16
CVE-2018-20217 MEDIUM 5.3 UPGRADE MITIGATE A Reachable Assertion issue was discovered in the KDC in MIT Kerberos 5 (aka krb5) before 1.17
CVE-2017-11368 MEDIUM 6.5 MITIGATE DOWNGRADE In MIT Kerberos 5 (aka krb5) 1.7 and later, an authenticated attacker can cause a KDC assertion failure by sen

References

← Back to latest CVEs