CVE-2021-36369

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.

Published: 2022-10-12 Last update: 2026-06-16 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-36369 is rated Moderate Risk (54.8/100): CVSS High severity, with medium exploitation likelihood (EPSS 1.35%). EPSS rose +1.14% over the last day, indicating growing attacker interest. Review affected assets and schedule remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2021-36369

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 0.21% 1.35% +1.14%
2 2026-04-28 0.12% 0.21% +0.09%
3 2025-11-21 — 0.12% —

Full EPSS history (7 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-36369

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
7.5 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:N)
Service keeps running; no real outage angle.
 3.9 3.6 [email protected]
7.5 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:N)
Service keeps running; no real outage angle.
 3.9 3.6 134c704f-9b21-4f2e-91b3-4a467353bcc0

Weakness enumeration for CVE-2021-36369

OS Trackers for CVE-2021-36369

vendor priority summary link
debian not yet assigned CVE-2021-36369 not yet assigned priority: Debian including 1 source packages (dropbear), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2021-36369
ubuntu medium CVE-2021-36369 medium priority: Ubuntu including 1 source packages (dropbear), 13 status rows across 13 suites (bionic, focal, jammy, kinetic, lunar, mantic, noble, oracular, plucky, questing, trusty, upstream, xenial): released 8, ignored 4, needed 1. https://ubuntu.com/security/CVE-2021-36369

Affected software / configurations for CVE-2021-36369

Vendor Product Version Raw CPE
dropbear_ssh_project dropbear_ssh <= 2020.81 cpe:2.3:a:dropbear_ssh_project:dropbear_ssh:*:*:*:*:*:*:*:*
debian debian_linux 10.0 cpe:2.3:o:debian:debian_linux:10.0:*:*:*:*:*:*:*

References for CVE-2021-36369

URL Tags
https://github.com/mkj/dropbear/pull/128 Third Party Advisory
https://github.com/mkj/dropbear/releases Release Notes Third Party Advisory
https://github.com/mkj/dropbear/releases/tag/DROPBEAR_2022.82 Release Notes Third Party Advisory
https://lists.debian.org/debian-lts-announce/2022/11/msg00015.html Mailing List Third Party Advisory
cvelogic Threat Intelligence