Update SSH Server crypto settings (#18697)

- Use a better and more curated list of Ciphers and KeyExchanges, these roughly follows OpenSSH's default.
- Remove some cryptography values which were deprecated.

3 files changed, 9 insertions, 9 deletions

diff --git a/custom/conf/app.example.ini b/custom/conf/app.example.ini
index f16b1d6a40..26de6dcd80 100644
--- a/custom/conf/app.example.ini
+++ b/custom/conf/app.example.ini
@@ -113,15 +113,15 @@ RUN_MODE = ; prod
 ;;
 ;; For the built-in SSH server, choose the ciphers to support for SSH connections,
 ;; for system SSH this setting has no effect
-;SSH_SERVER_CIPHERS = aes128-ctr, aes192-ctr, aes256-ctr, aes128-gcm@openssh.com, arcfour256, arcfour128
+;SSH_SERVER_CIPHERS = chacha20-poly1305@openssh.com, aes128-ctr, aes192-ctr, aes256-ctr, aes128-gcm@openssh.com, aes256-gcm@openssh.com
 ;;
 ;; For the built-in SSH server, choose the key exchange algorithms to support for SSH connections,
 ;; for system SSH this setting has no effect
-;SSH_SERVER_KEY_EXCHANGES = diffie-hellman-group1-sha1, diffie-hellman-group14-sha1, ecdh-sha2-nistp256, ecdh-sha2-nistp384, ecdh-sha2-nistp521, curve25519-sha256@libssh.org
+;SSH_SERVER_KEY_EXCHANGES = curve25519-sha256@libssh.org, ecdh-sha2-nistp256, ecdh-sha2-nistp384, ecdh-sha2-nistp521, diffie-hellman-group14-sha1
 ;;
 ;; For the built-in SSH server, choose the MACs to support for SSH connections,
 ;; for system SSH this setting has no effect
-;SSH_SERVER_MACS = hmac-sha2-256-etm@openssh.com, hmac-sha2-256, hmac-sha1, hmac-sha1-96
+;SSH_SERVER_MACS = hmac-sha2-256-etm@openssh.com, hmac-sha2-256, hmac-sha1
 ;;
 ;; For the built-in SSH server, choose the keypair to offer as the host key
 ;; The private key should be at SSH_SERVER_HOST_KEY and the public SSH_SERVER_HOST_KEY.pub
diff --git a/docs/content/doc/advanced/config-cheat-sheet.en-us.md b/docs/content/doc/advanced/config-cheat-sheet.en-us.md
index bc4675da1b..a7e5a62282 100644
--- a/docs/content/doc/advanced/config-cheat-sheet.en-us.md
+++ b/docs/content/doc/advanced/config-cheat-sheet.en-us.md
@@ -279,9 +279,9 @@ The following configuration set `Content-Type: application/vnd.android.package-a
 - `SSH_CREATE_AUTHORIZED_PRINCIPALS_FILE`: **false/true**: Gitea will create a authorized_principals file by default when it is not using the internal ssh server and `SSH_AUTHORIZED_PRINCIPALS_ALLOW` is not `off`.
 - `SSH_AUTHORIZED_PRINCIPALS_BACKUP`: **false/true**: Enable SSH Authorized Principals Backup when rewriting all keys, default is true if `SSH_AUTHORIZED_PRINCIPALS_ALLOW` is not `off`.
 - `SSH_AUTHORIZED_KEYS_COMMAND_TEMPLATE`: **{{.AppPath}} --config={{.CustomConf}} serv key-{{.Key.ID}}**: Set the template for the command to passed on authorized keys. Possible keys are: AppPath, AppWorkPath, CustomConf, CustomPath, Key - where Key is a `models/asymkey.PublicKey` and the others are strings which are shellquoted.
-- `SSH_SERVER_CIPHERS`: **aes128-ctr, aes192-ctr, aes256-ctr, aes128-gcm@openssh.com, arcfour256, arcfour128**: For the built-in SSH server, choose the ciphers to support for SSH connections, for system SSH this setting has no effect.
-- `SSH_SERVER_KEY_EXCHANGES`: **diffie-hellman-group1-sha1, diffie-hellman-group14-sha1, ecdh-sha2-nistp256, ecdh-sha2-nistp384, ecdh-sha2-nistp521, curve25519-sha256@libssh.org**: For the built-in SSH server, choose the key exchange algorithms to support for SSH connections, for system SSH this setting has no effect.
-- `SSH_SERVER_MACS`: **hmac-sha2-256-etm@openssh.com, hmac-sha2-256, hmac-sha1, hmac-sha1-96**: For the built-in SSH server, choose the MACs to support for SSH connections, for system SSH this setting has no effect
+- `SSH_SERVER_CIPHERS`: **chacha20-poly1305@openssh.com, aes128-ctr, aes192-ctr, aes256-ctr, aes128-gcm@openssh.com, aes256-gcm@openssh.com**: For the built-in SSH server, choose the ciphers to support for SSH connections, for system SSH this setting has no effect.
+- `SSH_SERVER_KEY_EXCHANGES`: **curve25519-sha256@libssh.org, ecdh-sha2-nistp256, ecdh-sha2-nistp384, ecdh-sha2-nistp521, diffie-hellman-group14-sha1**: For the built-in SSH server, choose the key exchange algorithms to support for SSH connections, for system SSH this setting has no effect.
+- `SSH_SERVER_MACS`: **hmac-sha2-256-etm@openssh.com, hmac-sha2-256, hmac-sha1**: For the built-in SSH server, choose the MACs to support for SSH connections, for system SSH this setting has no effect
 - `SSH_SERVER_HOST_KEYS`: **ssh/gitea.rsa, ssh/gogs.rsa**: For the built-in SSH server, choose the keypairs to offer as the host key. The private key should be at `SSH_SERVER_HOST_KEY` and the public `SSH_SERVER_HOST_KEY.pub`. Relative paths are made absolute relative to the `APP_DATA_PATH`. If no key exists a 4096 bit RSA key will be created for you.
 - `SSH_KEY_TEST_PATH`: **/tmp**: Directory to create temporary files in when testing public keys using ssh-keygen, default is the system temporary directory.
 - `SSH_KEYGEN_PATH`: **ssh-keygen**: Path to ssh-keygen, default is 'ssh-keygen' which means the shell is responsible for finding out which one to call.
diff --git a/modules/setting/setting.go b/modules/setting/setting.go
index cdfa1130f2..edbdbfa866 100644
--- a/modules/setting/setting.go
+++ b/modules/setting/setting.go
@@ -163,9 +163,9 @@ var (
 		StartBuiltinServer:            false,
 		Domain:                        "",
 		Port:                          22,
-		ServerCiphers:                 []string{"aes128-ctr", "aes192-ctr", "aes256-ctr", "aes128-gcm@openssh.com", "arcfour256", "arcfour128"},
-		ServerKeyExchanges:            []string{"diffie-hellman-group1-sha1", "diffie-hellman-group14-sha1", "ecdh-sha2-nistp256", "ecdh-sha2-nistp384", "ecdh-sha2-nistp521", "curve25519-sha256@libssh.org"},
-		ServerMACs:                    []string{"hmac-sha2-256-etm@openssh.com", "hmac-sha2-256", "hmac-sha1", "hmac-sha1-96"},
+		ServerCiphers:                 []string{"chacha20-poly1305@openssh.com", "aes128-ctr", "aes192-ctr", "aes256-ctr", "aes128-gcm@openssh.com", "aes256-gcm@openssh.com"},
+		ServerKeyExchanges:            []string{"curve25519-sha256@libssh.org", "ecdh-sha2-nistp256", "ecdh-sha2-nistp384", "ecdh-sha2-nistp521", "diffie-hellman-group14-sha1"},
+		ServerMACs:                    []string{"hmac-sha2-256-etm@openssh.com", "hmac-sha2-256", "hmac-sha1"},
 		KeygenPath:                    "ssh-keygen",
 		MinimumKeySizeCheck:           true,
 		MinimumKeySizes:               map[string]int{"ed25519": 256, "ed25519-sk": 256, "ecdsa": 256, "ecdsa-sk": 256, "rsa": 2048},