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sftpd: remove diffie-hellman-group18-sha512 KEX

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Signed-off-by: Nicola Murino <nicola.murino@gmail.com>
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Nicola Murino 2023-08-04 21:10:39 +02:00
parent af0d7b48ad
commit 75e6ef6132
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4 changed files with 10 additions and 5 deletions
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2
docs/full-configuration.md
View file

@ -140,7 +140,7 @@ The configuration file contains the following sections:
- `host_certificates`, list of strings. Public host certificates. Each certificate can be defined as a path relative to the configuration directory or an absolute one. Certificate's public key must match a private host key otherwise it will be silently ignored. Default: empty.
- `host_key_algorithms`, list of strings. Public key algorithms that the server will accept for host key authentication. The supported values are: `rsa-sha2-512-cert-v01@openssh.com`, `rsa-sha2-256-cert-v01@openssh.com`, `ssh-rsa-cert-v01@openssh.com`, `ssh-dss-cert-v01@openssh.com`, `ecdsa-sha2-nistp256-cert-v01@openssh.com`, `ecdsa-sha2-nistp384-cert-v01@openssh.com`, `ecdsa-sha2-nistp521-cert-v01@openssh.com`, `ssh-ed25519-cert-v01@openssh.com`, `ecdsa-sha2-nistp256`, `ecdsa-sha2-nistp384`, `ecdsa-sha2-nistp521`, `rsa-sha2-512`, `rsa-sha2-256`, `ssh-rsa`, `ssh-dss`, `ssh-ed25519`. Default values: `rsa-sha2-512-cert-v01@openssh.com`, `rsa-sha2-256-cert-v01@openssh.com`, `ecdsa-sha2-nistp256-cert-v01@openssh.com`, `ecdsa-sha2-nistp384-cert-v01@openssh.com`, `ecdsa-sha2-nistp521-cert-v01@openssh.com`, `ssh-ed25519-cert-v01@openssh.com`, `ecdsa-sha2-nistp256`, `ecdsa-sha2-nistp384`, `ecdsa-sha2-nistp521`, `rsa-sha2-512`, `rsa-sha2-256`, `ssh-ed25519`.
- `moduli`, list of strings. Diffie-Hellman moduli files. Each moduli file can be defined as a path relative to the configuration directory or an absolute one. If set and valid, `diffie-hellman-group-exchange-sha256` and `diffie-hellman-group-exchange-sha1` KEX algorithms will be available, `diffie-hellman-group-exchange-sha256` will be enabled by default if you don't explicitly set KEXs. Invalid moduli file will be silently ignored. Default: empty.
- `kex_algorithms`, list of strings. Available KEX (Key Exchange) algorithms in preference order. Leave empty to use default values. The supported values are: `curve25519-sha256`, `curve25519-sha256@libssh.org`, `ecdh-sha2-nistp256`, `ecdh-sha2-nistp384`, `ecdh-sha2-nistp521`, `diffie-hellman-group14-sha256`, `diffie-hellman-group16-sha512`, `diffie-hellman-group18-sha512`, `diffie-hellman-group14-sha1`, `diffie-hellman-group1-sha1`. Default values: `curve25519-sha256`, `curve25519-sha256@libssh.org`, `ecdh-sha2-nistp256`, `ecdh-sha2-nistp384`, `ecdh-sha2-nistp521`, `diffie-hellman-group14-sha256`. SHA512 based KEXs are disabled by default because they are slow. If you set one or more moduli files, `diffie-hellman-group-exchange-sha256` and `diffie-hellman-group-exchange-sha1` will be available.
- `kex_algorithms`, list of strings. Available KEX (Key Exchange) algorithms in preference order. Leave empty to use default values. The supported values are: `curve25519-sha256`, `curve25519-sha256@libssh.org`, `ecdh-sha2-nistp256`, `ecdh-sha2-nistp384`, `ecdh-sha2-nistp521`, `diffie-hellman-group14-sha256`, `diffie-hellman-group16-sha512`, `diffie-hellman-group14-sha1`, `diffie-hellman-group1-sha1`. Default values: `curve25519-sha256`, `curve25519-sha256@libssh.org`, `ecdh-sha2-nistp256`, `ecdh-sha2-nistp384`, `ecdh-sha2-nistp521`, `diffie-hellman-group14-sha256`. SHA512 based KEXs are disabled by default because they are slow. If you set one or more moduli files, `diffie-hellman-group-exchange-sha256` and `diffie-hellman-group-exchange-sha1` will be available.
- `ciphers`, list of strings. Allowed ciphers in preference order. Leave empty to use default values. The supported values are: `aes128-gcm@openssh.com`, `aes256-gcm@openssh.com`, `chacha20-poly1305@openssh.com`, `aes128-ctr`, `aes192-ctr`, `aes256-ctr`, `aes128-cbc`, `aes192-cbc`, `aes256-cbc`, `3des-cbc`, `arcfour256`, `arcfour128`, `arcfour`. Default values: `aes128-gcm@openssh.com`, `aes256-gcm@openssh.com`, `chacha20-poly1305@openssh.com`, `aes128-ctr`, `aes192-ctr`, `aes256-ctr`. Please note that the ciphers disabled by default are insecure, you should expect that an active attacker can recover plaintext if you enable them.
- `macs`, list of strings. Available MAC (message authentication code) algorithms in preference order. Leave empty to use default values. The supported values are: `hmac-sha2-256-etm@openssh.com`, `hmac-sha2-256`, `hmac-sha2-512-etm@openssh.com`, `hmac-sha2-512`, `hmac-sha1`, `hmac-sha1-96`. Default values: `hmac-sha2-256-etm@openssh.com`, `hmac-sha2-256`.
- `trusted_user_ca_keys`, list of public keys paths of certificate authorities that are trusted to sign user certificates for authentication. The paths can be absolute or relative to the configuration directory.

6
internal/dataprovider/configs.go
View file

@ -30,8 +30,7 @@ import (
var (
supportedHostKeyAlgos = []string{ssh.KeyAlgoRSA, ssh.CertAlgoRSAv01}
supportedKexAlgos = []string{
"diffie-hellman-group16-sha512", "diffie-hellman-group18-sha512",
"diffie-hellman-group14-sha1", "diffie-hellman-group1-sha1",
"diffie-hellman-group16-sha512", "diffie-hellman-group14-sha1", "diffie-hellman-group1-sha1",
"diffie-hellman-group-exchange-sha256", "diffie-hellman-group-exchange-sha1",
}
supportedCiphers = []string{
@ -104,6 +103,9 @@ func (c *SFTPDConfigs) validate() error {
}
}
for _, algo := range c.KexAlgorithms {
if algo == "diffie-hellman-group18-sha512" {
continue
}
if !util.Contains(supportedKexAlgos, algo) {
return util.NewValidationError(fmt.Sprintf("unsupported KEX algorithm %q", algo))
}

3
internal/sftpd/server.go
View file

@ -468,6 +468,9 @@ func (c *Configuration) configureSecurityOptions(serverConfig *ssh.ServerConfig)
}
c.KexAlgorithms = util.RemoveDuplicates(c.KexAlgorithms, true)
for _, kex := range c.KexAlgorithms {
if kex == "diffie-hellman-group18-sha512" {
logger.Warn(logSender, "", "KEX %q is not supported and will be ignored", kex)
}
if !util.Contains(supportedKexAlgos, kex) {
return fmt.Errorf("unsupported key-exchange algorithm %q", kex)
}

4
internal/vfs/sftpfs.go
View file

@ -939,8 +939,8 @@ func (c *sftpConnection) openConnNoLock() error {
"aes128-ctr", "aes192-ctr", "aes256-ctr", "aes128-cbc", "aes192-cbc", "aes256-cbc"}
clientConfig.KeyExchanges = []string{"curve25519-sha256", "curve25519-sha256@libssh.org",
"ecdh-sha2-nistp256", "ecdh-sha2-nistp384", "ecdh-sha2-nistp521",
"diffie-hellman-group14-sha256", "diffie-hellman-group16-sha512", "diffie-hellman-group18-sha512",
"diffie-hellman-group-exchange-sha256", "diffie-hellman-group-exchange-sha1",
"diffie-hellman-group14-sha256", "diffie-hellman-group-exchange-sha256",
"diffie-hellman-group16-sha512", "diffie-hellman-group-exchange-sha1",
"diffie-hellman-group14-sha1", "diffie-hellman-group1-sha1"}
clientConfig.MACs = []string{"hmac-sha2-256-etm@openssh.com", "hmac-sha2-256",
"hmac-sha2-512-etm@openssh.com", "hmac-sha2-512",