Software caused connection abort
What “Software caused connection abort” usually means
When PuTTY reports Software caused connection abort, the client has already attempted a network or protocol step and failed before a normal interactive shell is available. This guide explains what the message usually means on Windows clients, which local settings to verify first, and when the problem is almost certainly on the server, firewall, or DNS path rather than inside the PuTTY GUI.
Windows reported that local software aborted the socket—commonly security products, network filters, or abrupt interface changes (VPN tear-down).
Independent resource: Putty.info is educational only and is not affiliated with the official PuTTY project. Compare symptoms against the official documentation for your installed version.
Symptoms you will see
Operators usually notice this failure in one of a few repeatable ways. Capture the exact dialog text, the hostname and port from the Session panel, and whether the failure happens before or after a username prompt—those details decide which checklist below applies.
- Abort errors coinciding with VPN reconnects or docking/undocking.
- Sessions die when endpoint protection updates scan network stacks.
Likely causes ranked by frequency
Several independent conditions can produce the same client-facing wording. Work from the outside in: reachability first, protocol selection second, authentication third. Changing key files will not fix a TCP refusal, and opening a wider firewall will not fix a rejected public key.
- VPN client resetting routes mid-session.
- Firewall agents injecting into Winsock.
- NIC power management sleeping the adapter.
- Manual abort from another tool binding the same resources (rarer).
Step-by-step client checks
Use this ordered checklist on a workstation you control. Prefer saved sessions so Host Name, Port, and Connection type stay consistent while you isolate one variable at a time.
- Reproduce with VPN stably connected; avoid reconnect storms.
- Test after temporarily reviewing endpoint firewall logs (do not broadly disable security without IT approval).
- Disable NIC power-saving on corporate laptops if policy allows.
- Enable SSH keepalives carefully via Connection → seconds between keepalives—see keep-session-alive guide.
- Update PuTTY to current stable from official sources.
- Compare wired Ethernet versus Wi-Fi flakiness.
Do not paste private keys, passphrases, or production passwords into Putty.info tools or contact forms. Diagnose locally with PuTTY, Plink, PSCP, or PSFTP from an official install.
When it is a server or network issue
If only one client subnet sees aborts, suspect local middleboxes. If all clients abort when talking to one host, suspect server-side forced disconnects misreported through Windows wording.
If TCP connects from another network path but fails from yours, involve the network team with traceroute/path evidence rather than repeatedly regenerating keys. If authentication fails after a banner appears, collect the server sshd logs for the same timestamp and username—client-side retries alone rarely reveal AccountLocked, Match blocks, or AllowUsers denials.