How severe is CVE-2021-36367?

CVE-2021-36367 has a CVSS 3.x base score of 8.1, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is high, integrity high, and availability none.

Is CVE-2021-36367 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (62nd percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-36367?

CVE-2021-36367 affects Putty. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-36367?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2021-36367 published?

CVE-2021-36367 was published on 2021-07-09 and last updated on 2026-06-17.

CVE-2021-36367

CVE-2021-36367 is a high-severity vulnerability in Putty with a CVSS 3.x base score of 8.1. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-345.

Key facts

Severity: High (CVSS 3.x base score 8.1)
CVSS v2: 5.8
EPSS exploit prediction: 1% (62nd percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-345
Affected product: Putty
Published: 2021-07-09
Last modified: 2026-06-17

Description

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).

Frequently asked questions

What is CVE-2021-36367?: 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).
How severe is CVE-2021-36367?: CVE-2021-36367 has a CVSS 3.x base score of 8.1, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is high, integrity high, and availability none.
Is CVE-2021-36367 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (62nd percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-36367?: CVE-2021-36367 affects Putty. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-36367?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2021-36367 published?: CVE-2021-36367 was published on 2021-07-09 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:putty:putty:*:*:*:*:*:*:*:*

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