CVE-2021-36369: An issue was discovered in Dropbear through 2020.81

Q: How do I fix CVE-2021-36369?

dropbear ssh: upgrade to newer than 2020.81; debian linux: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Q: Is CVE-2021-36369 being exploited?

CVE-2021-36369 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2021-36369 affect?

CVE-2021-36369 affects dropbear ssh, debian linux. Severity is high (CVSS 7.5). An issue was discovered in Dropbear through 2020.81. Due to a non-RFC-compliant check of the available authentication methods in the client-side SSH code, it is possible for an SSH server to change the login process in its favor. This attac

Q: How urgent is CVE-2021-36369?

Priority 56/100. High severity; Remotely exploitable, no login, no user action; On your watchlist

This month

HIGH 7.5REMOTEWATCHLISTUPGRADEMITIGATE

CVE-2021-36369 is a high-severity flaw (CVSS 7.5) affecting dropbear ssh, debian linux. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

An issue was discovered in Dropbear through 2020.81. Due to a non-RFC-compliant check of the available authentication methods in the client-side SSH code, it is possible for an SSH server to change the login process in its favor. This attack can bypass additional security measures such as FIDO2 tokens or SSH-Askpass. Thus, it allows an attacker to abuse a forwarded agent for logging on to another server unnoticed.

Why this priority

High severity
Remotely exploitable, no login, no user action
On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	1.9% (top 21%)
CISA exploited list	No
Weakness	CWE-287
Published	2022-10-12
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: debian · dropbear ssh project

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

Am I affected?

Timeline

2022-10-12 21:15 UTCPublished CVE record published
2026-06-17 03:58 UTCUpdated Record last modified

dropbear ssh project dropbear ssh UPGRADE

Affected: <= 2020.81

Fixed in: newer than 2020.81

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy dropbear-ssh || rpm -q dropbear-ssh || dropbear-ssh --version

2. UPGRADE to newer than 2020.81 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade dropbear-ssh

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade dropbear-ssh

Note

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

debian debian linux MITIGATE

Affected: 10.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 10.0

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.

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-2021-36369?

dropbear ssh: upgrade to newer than 2020.81; debian linux: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2021-36369 being exploited?

CVE-2021-36369 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-2021-36369 affect?

CVE-2021-36369 affects dropbear ssh, debian linux. Severity is high (CVSS 7.5). An issue was discovered in Dropbear through 2020.81. Due to a non-RFC-compliant check of the available authentication methods in the client-side SSH code, it is possible for an SSH server to change the login process in its favor. This attac

How urgent is CVE-2021-36369?

Priority 56/100. High severity; Remotely exploitable, no login, no user action; On your watchlist

Software pages

Debian vulnerabilities

Related CVEs

CVE-2020-36254 HIGH 8.1 UPGRADE scp.c in Dropbear before 2020.79 mishandles the filename of
CVE-2019-12953 MEDIUM 5.3 UPGRADE Dropbear 2011.54 through 2018.76 has an inconsistent failure delay that may lead to revealing valid usernames,

References

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