GitHub SSH ssh-rsa brownout Nov 4: test your Git clients

On Wednesday, November 4, GitHub runs its first SSH brownout. For a period that day, GitHub will refuse the SHA-1 ssh-rsa signature type and the diffie-hellman-group-exchange-sha256 key exchange. Any Git client that still depends on them will fail to clone, pull or push over SSH. In September, GitHub turned off SHA-1 in HTTPS. This is the SSH half, and you have two days to find the clients it breaks.

What actually happened

GitHub announced the change on September 22. The schedule:

• October 14, 2026: new RSA SSH keys uploaded after this date must be at least 3072 bits. GitHub also enabled the post-quantum key exchange mlkem768x25519-sha256.
• November 4, 2026: first brownout of ssh-rsa and diffie-hellman-group-exchange-sha256.
• December 9, 2026: second brownout.
• January 13, 2027: permanent removal.

GitHub did not publish the brownout hours. GitHub Enterprise Server gets the removals in version 3.25.

Your RSA key itself is not the problem. GitHub notes that every RSA key can sign with SHA-2. The problem is an old client that only knows how to sign with SHA-1. GitHub lists the minimum versions that use RSA with SHA-2 by default:

• OpenSSH 7.2p1
• libssh2 1.11.0
• Go SSH 0.16.0
• PuTTY 0.82
• JSch 0.1.66 (mwiede fork)
• TeamCity 2021.2.3

If your Git remotes start with https://, none of this affects you.

Why it matters for your business

Your developers' laptops are fine. The risk is the machine nobody updates: a CI runner on an old base image, a deploy script on a legacy server, a Java build tool with an old JSch, a Windows box with an old PuTTY, an appliance that pulls config from a repo. Those fail on Wednesday, and then they work again, and someone calls it a GitHub outage.

Use the brownout as a free test. Before Wednesday, list every machine that talks to GitHub over SSH and check its client version. On Wednesday, watch for failed jobs and write down each one. Then fix them before January 13, when the failure does not go away.

The simplest fix where you can't upgrade the client: generate an Ed25519 key for that machine. GitHub says Ed25519 and ECDSA keys will keep working indefinitely.

Sources: GitHub Changelog.