CVE-2021-36367
PuTTY through 0.75 proceeds with establishing an SSH session even if it has never sent a...
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).
Attack profile
How easy it is to exploit
- Attack vector
- Network
- Complexity
- Low
- Privileges needed
- None
- User interaction
- Required
What an attacker can affect
- Confidentiality
- High
- Integrity
- High
- Availability
- None
Exploit likelihood
What each source reports
NVD Score used
8.1
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).
- Record
CVE-2021-36367- CVSS 3.1
- 8.1 High
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N - CVSS 2.0
- 5.8 Medium
AV:N/AC:M/Au:N/C:P/I:P/A:N - Weakness
- CWE-345
- Updated
- 2026-11-02
CVE List
8.1
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).
- Record
CVE-2021-36367- CVSS 3.1
- 8.1 High
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N - Weakness
- CWE-345
- Updated
- 2026-11-02
EUVDEUVD-2021-22987
8.1
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).
- Record
EUVD-2021-22987- CVSS 3.1
- 8.1 High
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N - Updated
- 2026-11-03
GitHub AdvisoriesGHSA-wccm-6vx2-7p8c
8.1
PuTTY through 0.75 proceeds with establishing an SSH session even if it has never sent a...
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).
- Record
GHSA-wccm-6vx2-7p8c- CVSS 3.1
- 8.1 High
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N - Weakness
- CWE-345
- Updated
- 2026-11-02
OSVALPINE-CVE-2021-36367
8.1
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).
- Record
ALPINE-CVE-2021-36367- CVSS 3.1
- 8.1 High
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N - Updated
- 2026-11-03
OSV
8.1
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).
- Record
CVE-2021-36367- CVSS 3.1
- 8.1 High
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N - Updated
- 2026-11-02
OSVDEBIAN-CVE-2021-36367
8.1
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).
- Record
DEBIAN-CVE-2021-36367- CVSS 3.1
- 8.1 High
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N - Updated
- 2026-11-02
OSVUBUNTU-CVE-2021-36367
8.1
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).
- Record
UBUNTU-CVE-2021-36367- CVSS 3.1
- 8.1 High
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N - Updated
- 2026-11-02
Affected products
Affected packages
| Package | Affected | Fixed |
|---|---|---|
puttyAlpine:v3.11 |
before 0.76-r0 | 0.76-r0 |
puttyAlpine:v3.12 |
before 0.76-r0 | 0.76-r0 |
puttyAlpine:v3.13 |
before 0.76-r0 | 0.76-r0 |
puttyAlpine:v3.14 |
before 0.76-r0 | 0.76-r0 |
puttyAlpine:v3.15 |
before 0.76-r0 | 0.76-r0 |
puttyAlpine:v3.16 |
before 0.76-r0 | 0.76-r0 |
puttyAlpine:v3.17 |
before 0.76-r0 | 0.76-r0 |
puttyAlpine:v3.18 |
before 0.76-r0 | 0.76-r0 |
puttyAlpine:v3.19 |
before 0.76-r0 | 0.76-r0 |
puttyAlpine:v3.20 |
before 0.76-r0 | 0.76-r0 |
Show 12 moreShow less
| Package | Affected | Fixed |
|---|---|---|
puttyAlpine:v3.21 |
before 0.76-r0 | 0.76-r0 |
puttyAlpine:v3.22 |
before 0.76-r0 | 0.76-r0 |
puttyAlpine:v3.23 |
before 0.76-r0 | 0.76-r0 |
puttyAlpine:v3.24 |
before 0.76-r0 | 0.76-r0 |
puttyDebian:12 |
before 0.75-3 | 0.75-3 |
puttyDebian:13 |
before 0.75-3 | 0.75-3 |
puttyDebian:14 |
before 0.75-3 | 0.75-3 |
puttyDebian:10 |
before 0.74-1+deb11u1~deb10u1, plus listed versions 0.70-60.71-10.72-10.72-20.73-10.73-20.73-30.74-1 |
0.74-1+deb11u1~deb10u1 |
puttyUbuntu:16.04:LTS |
All versions, plus listed versions 0.65-20.66-10.66-20.66-30.66-4 Show 4 moreShow less0.67-10.67-20.67-3build0.16.04.10.67-3+deb9u1build0.16.04.1 |
None known |
puttyUbuntu:18.04:LTS |
All versions, plus listed versions 0.70-10.70-20.70-30.70-4 |
None known |
puttyUbuntu:20.04:LTS |
All versions, plus listed versions 0.72-10.73-10.73-2 |
None known |
puttyUbuntu:22.04:LTS |
All versions, plus listed versions 0.75-30.76-10.76-2 |
None known |
History
| Recorded | Changed | Sources |
|---|---|---|
| affected | OSV | |
| aliases | EUVD | |
| first indexed | CVE List, GitHub Advisories, NVD, OSV |
Dates are when Every CVE recorded each change. Upstream dates may differ.
In short
CVE-2021-36367 is a high vulnerability (CVSS 8.1) in Putty, published July 9, 2021. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 1.11%, the 65th percentile. Fixed in putty 0.76-r0.
References
chiark.greenend.org.uk/~sgtatham/putty/changes.html
git.tartarus.org?p=simon/putty.git%3Ba=commit%3Bh=1dc5659aa62848f0aeb5de7bd3839fecc7debefa
debian.org/security/2023/dsa-5588
lists.debian.org/debian-lts-announce/2024/04/msg00016.html
nvd.nist.gov/vuln/detail/CVE-2021-36367
git.tartarus.org?p=simon/putty.git;a=commit;h=1dc5659aa62848f0aeb5de7bd3839fecc7debefa