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Vulnerability details: VCID-cazr-yctb-n3bu
Vulnerability ID VCID-cazr-yctb-n3bu
Aliases CVE-2021-36367
Summary PuTTY through 0.75 proceeds with establishing an SSH session even if it has never sent a substantive authentication response. This makes it easier for an attacker-controlled SSH server to present a later spoofed authentication prompt (that the attacker can use to capture credential data, and use that data for purposes that are undesired by the client user).
Status Published
Exploitability 0.5
Weighted Severity 7.3
Risk 3.6
Affected and Fixed Packages Package Details
Weaknesses (1)
CWE-345 Insufficient Verification of Data Authenticity
System Score Found at
epss 0.00135 https://api.first.org/data/v1/epss?cve=CVE-2021-36367
epss 0.00135 https://api.first.org/data/v1/epss?cve=CVE-2021-36367
epss 0.00135 https://api.first.org/data/v1/epss?cve=CVE-2021-36367
epss 0.00135 https://api.first.org/data/v1/epss?cve=CVE-2021-36367
epss 0.00135 https://api.first.org/data/v1/epss?cve=CVE-2021-36367
epss 0.00135 https://api.first.org/data/v1/epss?cve=CVE-2021-36367
epss 0.00135 https://api.first.org/data/v1/epss?cve=CVE-2021-36367
epss 0.00135 https://api.first.org/data/v1/epss?cve=CVE-2021-36367
epss 0.00135 https://api.first.org/data/v1/epss?cve=CVE-2021-36367
epss 0.00135 https://api.first.org/data/v1/epss?cve=CVE-2021-36367
epss 0.00135 https://api.first.org/data/v1/epss?cve=CVE-2021-36367
epss 0.00135 https://api.first.org/data/v1/epss?cve=CVE-2021-36367
epss 0.00135 https://api.first.org/data/v1/epss?cve=CVE-2021-36367
epss 0.00135 https://api.first.org/data/v1/epss?cve=CVE-2021-36367
epss 0.00135 https://api.first.org/data/v1/epss?cve=CVE-2021-36367
epss 0.00135 https://api.first.org/data/v1/epss?cve=CVE-2021-36367
epss 0.00135 https://api.first.org/data/v1/epss?cve=CVE-2021-36367
cvssv3.1 8.1 https://git.tartarus.org/?p=simon/putty.git%3Ba=commit%3Bh=1dc5659aa62848f0aeb5de7bd3839fecc7debefa
ssvc Track https://git.tartarus.org/?p=simon/putty.git%3Ba=commit%3Bh=1dc5659aa62848f0aeb5de7bd3839fecc7debefa
cvssv3.1 8.1 https://lists.debian.org/debian-lts-announce/2024/04/msg00016.html
ssvc Track https://lists.debian.org/debian-lts-announce/2024/04/msg00016.html
cvssv2 5.8 https://nvd.nist.gov/vuln/detail/CVE-2021-36367
cvssv3.1 8.1 https://nvd.nist.gov/vuln/detail/CVE-2021-36367
archlinux Low https://security.archlinux.org/AVG-2143
cvssv3.1 8.1 https://www.chiark.greenend.org.uk/~sgtatham/putty/changes.html
ssvc Track https://www.chiark.greenend.org.uk/~sgtatham/putty/changes.html
cvssv3.1 8.1 https://www.debian.org/security/2023/dsa-5588
ssvc Track https://www.debian.org/security/2023/dsa-5588
Reference id Reference type URL
https://api.first.org/data/v1/epss?cve=CVE-2021-36367
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-36367
https://lists.debian.org/debian-lts-announce/2024/04/msg00016.html
https://www.chiark.greenend.org.uk/~sgtatham/putty/changes.html
https://www.debian.org/security/2023/dsa-5588
990901 https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=990901
ASA-202107-37 https://security.archlinux.org/ASA-202107-37
AVG-2143 https://security.archlinux.org/AVG-2143
cpe:2.3:a:putty:putty:*:*:*:*:*:*:*:* https://nvd.nist.gov/vuln/search/results?adv_search=true&isCpeNameSearch=true&query=cpe:2.3:a:putty:putty:*:*:*:*:*:*:*:*
CVE-2021-36367 https://nvd.nist.gov/vuln/detail/CVE-2021-36367
putty.git%3Ba=commit%3Bh=1dc5659aa62848f0aeb5de7bd3839fecc7debefa https://git.tartarus.org/?p=simon/putty.git%3Ba=commit%3Bh=1dc5659aa62848f0aeb5de7bd3839fecc7debefa
No exploits are available.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N Found at https://git.tartarus.org/?p=simon/putty.git%3Ba=commit%3Bh=1dc5659aa62848f0aeb5de7bd3839fecc7debefa
Attack Vector (AV) Attack Complexity (AC) Privileges Required (PR) User Interaction (UI) Scope (S) Confidentiality Impact (C) Integrity Impact (I) Availability Impact (A)

network

adjacent_network

local

physical

low

high

none

low

high

none

required

unchanged

changed

high

low

none

high

low

none

high

low

none
Vector: SSVCv2/E:N/A:N/T:T/P:M/B:A/M:M/D:T/2024-02-22T20:07:50Z/ Found at https://git.tartarus.org/?p=simon/putty.git%3Ba=commit%3Bh=1dc5659aa62848f0aeb5de7bd3839fecc7debefa
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N Found at https://lists.debian.org/debian-lts-announce/2024/04/msg00016.html
Attack Vector (AV) Attack Complexity (AC) Privileges Required (PR) User Interaction (UI) Scope (S) Confidentiality Impact (C) Integrity Impact (I) Availability Impact (A)

network

adjacent_network

local

physical

low

high

none

low

high

none

required

unchanged

changed

high

low

none

high

low

none

high

low

none
Vector: SSVCv2/E:N/A:N/T:T/P:M/B:A/M:M/D:T/2024-02-22T20:07:50Z/ Found at https://lists.debian.org/debian-lts-announce/2024/04/msg00016.html
Vector: AV:N/AC:M/Au:N/C:P/I:P/A:N Found at https://nvd.nist.gov/vuln/detail/CVE-2021-36367
Exploitability (E) Access Vector (AV) Access Complexity (AC) Authentication (Au) Confidentiality Impact (C) Integrity Impact (I) Availability Impact (A)

high

functional

unproven

proof_of_concept

not_defined

local

adjacent_network

network

high

medium

low

multiple

single

none

none

partial

complete

none

partial

complete

none

partial

complete
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N Found at https://nvd.nist.gov/vuln/detail/CVE-2021-36367
Attack Vector (AV) Attack Complexity (AC) Privileges Required (PR) User Interaction (UI) Scope (S) Confidentiality Impact (C) Integrity Impact (I) Availability Impact (A)

network

adjacent_network

local

physical

low

high

none

low

high

none

required

unchanged

changed

high

low

none

high

low

none

high

low

none
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N Found at https://www.chiark.greenend.org.uk/~sgtatham/putty/changes.html
Attack Vector (AV) Attack Complexity (AC) Privileges Required (PR) User Interaction (UI) Scope (S) Confidentiality Impact (C) Integrity Impact (I) Availability Impact (A)

network

adjacent_network

local

physical

low

high

none

low

high

none

required

unchanged

changed

high

low

none

high

low

none

high

low

none
Vector: SSVCv2/E:N/A:N/T:T/P:M/B:A/M:M/D:T/2024-02-22T20:07:50Z/ Found at https://www.chiark.greenend.org.uk/~sgtatham/putty/changes.html
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N Found at https://www.debian.org/security/2023/dsa-5588
Attack Vector (AV) Attack Complexity (AC) Privileges Required (PR) User Interaction (UI) Scope (S) Confidentiality Impact (C) Integrity Impact (I) Availability Impact (A)

network

adjacent_network

local

physical

low

high

none

low

high

none

required

unchanged

changed

high

low

none

high

low

none

high

low

none
Vector: SSVCv2/E:N/A:N/T:T/P:M/B:A/M:M/D:T/2024-02-22T20:07:50Z/ Found at https://www.debian.org/security/2023/dsa-5588
Exploit Prediction Scoring System (EPSS)
Percentile 0.34083
EPSS Score 0.00135
Published At July 30, 2025, 12:55 p.m.
Date Actor Action Source VulnerableCode Version
2025-07-31T08:35:46.813125+00:00 Alpine Linux Importer Import https://secdb.alpinelinux.org/v3.18/main.json 37.0.0