CVE-2020-10188: utility.c in telnetd in netkit telnet through 0.17 allows remote attackers to execute arbitrary code via short

This week

CRITICAL 9.8REMOTEWATCHLISTUPGRADEMITIGATEMITIGATE

CVE-2020-10188 is a critical-severity flaw (CVSS 9.8) affecting netkit telnet, fedora, debian linux. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

utility.c in telnetd in netkit telnet through 0.17 allows remote attackers to execute arbitrary code via short writes or urgent data, because of a buffer overflow involving the netclear and nextitem functions.

Why this priority

Critical severity
EPSS top 1%: very likely to be exploited
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	74.3% (top 1%)
CISA exploited list	No
Weakness	CWE-120
Published	2020-03-06
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: arista · debian · fedoraproject · juniper · netkit telnet project · oracle

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2020-03-06 15:15 UTCPublished CVE record published
2026-06-17 02:47 UTCUpdated Record last modified

netkit telnet project netkit telnet UPGRADE

Affected: <= 0.17

Fixed in: newer than 0.17

Safe to downgrade to: no unaffected older release

1. Check installed version

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

2. UPGRADE to newer than 0.17 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade netkit-telnet

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade netkit-telnet

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

fedoraproject fedora MITIGATE

Affected: 30 · 31 · 32

Fixed in: no fixed release known

Safe to downgrade to: a release before 30

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.

debian debian linux MITIGATE

Affected: 8.0 · 9.0

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.

arista eos UPGRADE

Affected: <= 4.20.15 · >= 4.21.0 and <= 4.21.10m · >= 4.22 and <= 4.22.4m · >= 4.23 and <= 4.23.3m · 4.24.0f

Fixed in: newer than 4.23.3m

Safe to downgrade to: a release before 4.21.0

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.

oracle communications performance intelligence center DOWNGRADE

Affected: 10.4.0.2

Fixed in: no fixed release known

Safe to downgrade to: a release before 10.4.0.2

1. Check installed version

apt-cache policy communications-performance-intelligence-center || rpm -q communications-performance-intelligence-center || communications-performance-intelligence-center --version

2. No fixed release: DOWNGRADE to a release before 10.4.0.2 (Debian / Ubuntu)

apt-cache madison communications-performance-intelligence-center sudo apt install communications-performance-intelligence-center=<VERSION_BEFORE_10.4.0.2> sudo apt-mark hold communications-performance-intelligence-center

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

dnf --showduplicates list communications-performance-intelligence-center sudo dnf downgrade communications-performance-intelligence-center-<VERSION_BEFORE_10.4.0.2> sudo dnf versionlock add communications-performance-intelligence-center

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.

juniper junos MITIGATE

Affected: 12.3 · 12.3 r1 · 12.3 r10 · 12.3 r10-s1 · 12.3 r10-s2 · 12.3 r11 · 12.3 r12 · 12.3 r12-s1

Fixed in: no fixed release known

Safe to downgrade to: a release before 12.3

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 · lis · FIXED · 2.1.21-2.fc46 · FEDORA-2026-039245acc6 · source

sudo dnf upgrade --advisory=FEDORA-2026-039245acc6

Fedora ELN · bitcoin-core · FIXED · 32.1-2.eln159 · FEDORA-2026-41e13beebe · source

sudo dnf upgrade --advisory=FEDORA-2026-41e13beebe

Debian 12 · inetutils · FIXED · 2:1.9.4-12

sudo apt update && sudo apt install --only-upgrade inetutils dpkg --compare-versions "$(dpkg-query -W -f='${Version}' inetutils)" ge "2:1.9.4-12" && echo PATCHED || echo STILL-VULNERABLE

Debian 13 · inetutils · FIXED · 2:1.9.4-12

sudo apt update && sudo apt install --only-upgrade inetutils dpkg --compare-versions "$(dpkg-query -W -f='${Version}' inetutils)" ge "2:1.9.4-12" && echo PATCHED || echo STILL-VULNERABLE

Debian 12 · netkit-telnet-ssl · FIXED · 0.17.17+0.1-2woody3

sudo apt update && sudo apt install --only-upgrade netkit-telnet-ssl dpkg --compare-versions "$(dpkg-query -W -f='${Version}' netkit-telnet-ssl)" ge "0.17.17+0.1-2woody3" && echo PATCHED || echo STILL-VULNERABLE

Debian 13 · netkit-telnet-ssl · FIXED · 0.17.17+0.1-2woody3

RHEL 6 · telnet · FIXED · telnet-0.17-49.el6_10

sudo dnf upgrade --advisory=RHSA-2020:1335 rpm -q telnet

RHEL 6 · krb5-appl · FIXED · krb5-appl-1.0.1-10.el6_10

sudo dnf upgrade --advisory=RHSA-2020:1349 rpm -q krb5-appl

RHEL 7 · telnet · FIXED · telnet-0.17-65.el7_8

sudo dnf upgrade --advisory=RHSA-2020:1334 rpm -q telnet

RHEL 7.6 Advanced Update Support · telnet · FIXED · telnet-0.17-65.el7_6

sudo dnf upgrade --advisory=RHSA-2022:0011 rpm -q telnet

RHEL 7.6 Telco Extended Update Support · telnet · FIXED · telnet-0.17-65.el7_6

sudo dnf upgrade --advisory=RHSA-2022:0011 rpm -q telnet

Amazon Linux 2 · see advisory · FIXED · ALAS2-2020-1422 · source

sudo yum update --advisory=ALAS2-2020-1422

Amazon Linux 1 · see advisory · FIXED · ALAS-2020-1387 · source

sudo yum update --advisory=ALAS-2020-1387

Public exploits and detection

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

Write-up: appgateresearch.blogspot.com/2020/02/bravestarr-fedora-31-netkit-telnetd_28.html
Write-up: tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-telnetd-EFJrEzPx
Write-up: www.oracle.com/security-alerts/cpuApr2021.html

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-2020-10188?

netkit telnet: upgrade to newer than 0.17; fedora: mitigate or apply the listed mitigation; debian linux: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2020-10188 being exploited?

CVE-2020-10188 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-2020-10188 affect?

CVE-2020-10188 affects netkit telnet, fedora, debian linux. Severity is critical (CVSS 9.8). utility.c in telnetd in netkit telnet through 0.17 allows remote attackers to execute arbitrary code via short writes or urgent data, because of a buffer overflow involving the netclear and nextitem functions.

How urgent is CVE-2020-10188?

Priority 69/100. Critical severity; EPSS top 1%: very likely to be exploited; Remotely exploitable, no login, no user action; On your watchlist

Software pages

Debian vulnerabilities · Juniper Junos vulnerabilities

References

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