Skip to content
Fencer Vulns
high 8.1

CVE-2021-36367 json

PuTTY through 0.75 proceeds with establishing an SSH session even if it has never sent a substantive authentication response.

published 2021-07-09 5 y ago modified 2026-06-17 4 mo ago also EUVD-2021-22987

cvss
8.1
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
1.1%
EPSS 1.1% chance of exploitation in 30 days, percentile 66%
public exploits
0
none known

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).

Patch / fix

  • putty Debian 14, Debian 13, Debian 12 0.75-3

debian advisories DEBIAN-CVE-2021-36367

  • putty Alpine 3.24, Alpine 3.23, Alpine 3.22 +11 more 0.76-r0

alpine advisories ALPINE-CVE-2021-36367

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • putty Arch Linux 0.76-1

arch linux advisories AVG-2143

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-36367 updated cvss 8.1

putty: weak ssh authentication procedure may lead to credentials disclosure

  • Red Hat All currently supported Red Hat products
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
total
Assessed
2 y ago

Exploit prediction

1.11% chance of exploitation in the next 30 days, higher than 66% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CISA ADP 3.1 8.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N
NVD 3.1 8.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N
CNA 3.1 8.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N
NVD 2.0 5.8 AV:N/AC:M/Au:N/C:P/I:P/A:N

Affected products

  • putty putty

Classification

Weakness
  • CWE-345 Insufficient Verification of Data Authenticity

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.