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support cram-md5 authentication for imap and smtp

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and change thunderbird autoconfiguration to use it.

unfortunately, for microsoft autodiscover, there appears to be no way to
request secure password negotiation. so it will default to plain text auth.

cram-md5 is less secure than scram-sha-*, but thunderbird does not yet support
scram auth. it currently chooses "plain", sending the literal password over the
connection (which is TLS-protected, but we don't want to receive clear text
passwords). in short, cram-md5 is better than nothing...

for cram-md5 to work, a new set of derived credentials need to be stored in the
database. so you need to save your password again to make it work. this was
also the case with the scram-sha-1 addition, but i forgot to mention it then.
This commit is contained in:
Mechiel Lukkien
2023-02-05 16:29:03 +01:00
parent f83fe79f96
commit e52c9d36a6
9 changed files with 306 additions and 22 deletions
Download Patch File Download Diff File Expand all files Collapse all files

75
smtpserver/server.go
View File

@ -5,6 +5,7 @@ import (
"bufio"
"bytes"
"context"
"crypto/md5"
"crypto/rsa"
"crypto/sha1"
"crypto/sha256"
@ -682,7 +683,7 @@ func (c *conn) cmdHello(p *parser, ehlo bool) {
if c.submission {
// ../rfc/4954:123
if c.tls || !c.requireTLSForAuth {
c.bwritelinef("250-AUTH PLAIN SCRAM-SHA-256 SCRAM-SHA-1")
c.bwritelinef("250-AUTH PLAIN SCRAM-SHA-256 SCRAM-SHA-1 CRAM-MD5")
} else {
c.bwritelinef("250-AUTH ")
}
@ -864,6 +865,75 @@ func (c *conn) cmdAuth(p *parser) {
// ../rfc/4954:276
c.writecodeline(smtp.C235AuthSuccess, smtp.SePol7Other0, "nice", nil)
case "CRAM-MD5":
authVariant = strings.ToLower(mech)
p.xempty()
// ../rfc/2195:82
chal := fmt.Sprintf("<%d.%d@%s>", uint64(mox.CryptoRandInt()), time.Now().UnixNano(), mox.Conf.Static.HostnameDomain.ASCII)
c.writelinef("%d %s", smtp.C334ContinueAuth, base64.StdEncoding.EncodeToString([]byte(chal)))
resp := xreadContinuation()
t := strings.Split(string(resp), " ")
if len(t) != 2 || len(t[1]) != 2*md5.Size {
xsmtpUserErrorf(smtp.C501BadParamSyntax, smtp.SeProto5BadParams4, "malformed cram-md5 response")
}
addr := t[0]
c.log.Info("cram-md5 auth", mlog.Field("address", addr))
acc, _, err := store.OpenEmail(addr)
if err != nil {
if errors.Is(err, store.ErrUnknownCredentials) {
xsmtpUserErrorf(smtp.C535AuthBadCreds, smtp.SePol7AuthBadCreds8, "bad user/pass")
}
}
xcheckf(err, "looking up address")
defer func() {
if acc != nil {
err := acc.Close()
if err != nil {
c.log.Errorx("closing account", err)
}
}
}()
var ipadhash, opadhash hash.Hash
acc.WithRLock(func() {
err := acc.DB.Read(func(tx *bstore.Tx) error {
password, err := bstore.QueryTx[store.Password](tx).Get()
if err == bstore.ErrAbsent {
xsmtpUserErrorf(smtp.C535AuthBadCreds, smtp.SePol7AuthBadCreds8, "bad user/pass")
}
if err != nil {
return err
}
ipadhash = password.CRAMMD5.Ipad
opadhash = password.CRAMMD5.Opad
return nil
})
xcheckf(err, "tx read")
})
if ipadhash == nil || opadhash == nil {
c.log.Info("cram-md5 auth attempt without derived secrets set, save password again to store secrets", mlog.Field("address", addr))
xsmtpUserErrorf(smtp.C535AuthBadCreds, smtp.SePol7AuthBadCreds8, "bad user/pass")
}
// ../rfc/2195:138 ../rfc/2104:142
ipadhash.Write([]byte(chal))
opadhash.Write(ipadhash.Sum(nil))
digest := fmt.Sprintf("%x", opadhash.Sum(nil))
if digest != t[1] {
xsmtpUserErrorf(smtp.C535AuthBadCreds, smtp.SePol7AuthBadCreds8, "bad user/pass")
}
authResult = "ok"
c.authFailed = 0
c.account = acc
acc = nil // Cancel cleanup.
c.username = addr
// ../rfc/4954:276
c.writecodeline(smtp.C235AuthSuccess, smtp.SePol7Other0, "nice", nil)
case "SCRAM-SHA-1", "SCRAM-SHA-256":
// 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
@ -910,6 +980,7 @@ func (c *conn) cmdAuth(p *parser) {
xscram = password.SCRAMSHA256
}
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", mlog.Field("address", ss.Authentication))
xsmtpUserErrorf(smtp.C454TempAuthFail, smtp.SeSys3Other0, "scram not possible")
}
xcheckf(err, "fetching credentials")
@ -947,8 +1018,6 @@ func (c *conn) cmdAuth(p *parser) {
c.writecodeline(smtp.C235AuthSuccess, smtp.SePol7Other0, "nice", nil)
default:
// todo future: implement scram-sha-256 ../rfc/7677
// todo future: possibly implement cram-md5, at least where we allow PLAIN. ../rfc/4954:348
// ../rfc/4954:176
xsmtpUserErrorf(smtp.C504ParamNotImpl, smtp.SeProto5BadParams4, "mechanism %s not supported", mech)
}