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implement the plus variants of scram, to bind the authentication exchange to the tls connection

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to get the security benefits (detecting mitm attempts), explicitly configure
clients to use a scram plus variant, e.g. scram-sha-256-plus. unfortunately,
not many clients support it yet.

imapserver scram plus support seems to work with the latest imtest (imap test
client) from cyrus-sasl. no success yet with mutt (with gsasl) though.
This commit is contained in:
Mechiel Lukkien
2023-12-23 23:07:21 +01:00
parent 4701857d7f
commit e7478ed6ac
23 changed files with 690 additions and 189 deletions
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50
imapserver/server.go
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@ -150,13 +150,18 @@ var authFailDelay = time.Second // After authentication failure.
// SPECIAL-USE: ../rfc/6154
// LIST-STATUS: ../rfc/5819
// ID: ../rfc/2971
// AUTH=SCRAM-SHA-256: ../rfc/7677 ../rfc/5802
// AUTH=SCRAM-SHA-1: ../rfc/5802
// AUTH=SCRAM-SHA-256-PLUS and AUTH=SCRAM-SHA-256: ../rfc/7677 ../rfc/5802
// AUTH=SCRAM-SHA-1-PLUS and AUTH=SCRAM-SHA-1: ../rfc/5802
// AUTH=CRAM-MD5: ../rfc/2195
// APPENDLIMIT, we support the max possible size, 1<<63 - 1: ../rfc/7889:129
// CONDSTORE: ../rfc/7162:411
// QRESYNC: ../rfc/7162:1323
const serverCapabilities = "IMAP4rev2 IMAP4rev1 ENABLE LITERAL+ IDLE SASL-IR BINARY UNSELECT UIDPLUS ESEARCH SEARCHRES MOVE UTF8=ONLY LIST-EXTENDED SPECIAL-USE LIST-STATUS AUTH=SCRAM-SHA-256 AUTH=SCRAM-SHA-1 AUTH=CRAM-MD5 ID APPENDLIMIT=9223372036854775807 CONDSTORE QRESYNC"
//
// We always announce support for SCRAM PLUS-variants, also on connections without
// TLS. The client should not be selecting PLUS variants on non-TLS connections,
// instead opting to do the bare SCRAM variant without indicating the server claims
// to support the PLUS variant (skipping the server downgrade detection check).
const serverCapabilities = "IMAP4rev2 IMAP4rev1 ENABLE LITERAL+ IDLE SASL-IR BINARY UNSELECT UIDPLUS ESEARCH SEARCHRES MOVE UTF8=ONLY LIST-EXTENDED SPECIAL-USE LIST-STATUS AUTH=SCRAM-SHA-256-PLUS AUTH=SCRAM-SHA-256 AUTH=SCRAM-SHA-1-PLUS AUTH=SCRAM-SHA-1 AUTH=CRAM-MD5 ID APPENDLIMIT=9223372036854775807 CONDSTORE QRESYNC"
type conn struct {
cid int64
@ -1654,22 +1659,34 @@ func (c *conn) cmdAuthenticate(tag, cmd string, p *parser) {
acc = nil // Cancel cleanup.
c.username = addr
case "SCRAM-SHA-1", "SCRAM-SHA-256":
case "SCRAM-SHA-256-PLUS", "SCRAM-SHA-256", "SCRAM-SHA-1-PLUS", "SCRAM-SHA-1":
// todo: improve handling of errors during scram. e.g. invalid parameters. should we abort the imap command, or continue until the end and respond with a scram-level error?
// todo: use single implementation between ../imapserver/server.go and ../smtpserver/server.go
authVariant = strings.ToLower(authType)
var h func() hash.Hash
if authVariant == "scram-sha-1" {
h = sha1.New
} else {
h = sha256.New
}
// No plaintext credentials, we can log these normally.
authVariant = strings.ToLower(authType)
var h func() hash.Hash
switch authVariant {
case "scram-sha-1", "scram-sha-1-plus":
h = sha1.New
case "scram-sha-256", "scram-sha-256-plus":
h = sha256.New
default:
xserverErrorf("missing case for scram variant")
}
var cs *tls.ConnectionState
requireChannelBinding := strings.HasSuffix(authVariant, "-plus")
if requireChannelBinding && !c.tls {
xuserErrorf("cannot use plus variant with tls channel binding without tls")
}
if c.tls {
xcs := c.conn.(*tls.Conn).ConnectionState()
cs = &xcs
}
c0 := xreadInitial()
ss, err := scram.NewServer(h, c0)
ss, err := scram.NewServer(h, c0, cs, requireChannelBinding)
if err != nil {
xsyntaxErrorf("starting scram: %s", err)
}
@ -1694,10 +1711,13 @@ func (c *conn) cmdAuthenticate(tag, cmd string, p *parser) {
acc.WithRLock(func() {
err := acc.DB.Read(context.TODO(), func(tx *bstore.Tx) error {
password, err := bstore.QueryTx[store.Password](tx).Get()
if authVariant == "scram-sha-1" {
switch authVariant {
case "scram-sha-1", "scram-sha-1-plus":
xscram = password.SCRAMSHA1
} else {
case "scram-sha-256", "scram-sha-256-plus":
xscram = password.SCRAMSHA256
default:
xserverErrorf("missing case for scram credentials")
}
if err == bstore.ErrAbsent || err == nil && (len(xscram.Salt) == 0 || xscram.Iterations == 0 || len(xscram.SaltedPassword) == 0) {
c.log.Info("scram auth attempt without derived secrets set, save password again to store secrets", slog.String("address", ss.Authentication))