No supported authentication methods available – SSH‑1 support decision

Background

PuTTY’s error message No supported authentication methods available appears when a server offers only legacy authentication mechanisms that the client does not enable. The client still exposes a Use SSH‑1 option, even though SSH‑1 is deprecated and considered insecure by most modern SSH servers.

Unresolved Decision

PuTTY’s source comments and recent release notes indicate that SSH‑1 support is retained for backward‑compatibility, yet no definitive timeline for its removal has been published. For low‑traffic workloads—where connections are infrequent and cost minimisation is a priority—this uncertainty creates a security cost: enabling SSH‑1 may expose the client to known vulnerabilities, while disabling it could prevent access to legacy systems.

Key Questions

• Will future PuTTY releases drop the SSH‑1 option, and if so, when?
• What are the measurable security and cost implications of leaving SSH‑1 enabled for low‑traffic connections?
• Are there client‑side configuration alternatives that allow legacy authentication without retaining the SSH‑1 option?