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https://github.com/mjl-/mox.git
synced 2025-07-10 09:54:40 +03:00
add faq for smtp smuggling, fix bug around handling "\nX\n" for any X, reject bare carriage returns and possibly smtp-smuggling attempts
mox was already strict in its "\r\n.\r\n" handling for end-of-message in an smtp transaction. due to a mostly unrelated bug, sequences of "\nX\n", including "\n.\n" were rejected with a "local processing error". the sequence "\r\n.\n" dropped the dot, not necessarily a big problem, this is unlikely to happen in a legimate transaction and the behaviour not unreasonable. we take this opportunity to reject all bare \r. we detect all slightly incorrect combinations of "\r\n.\r\n" with an error mentioning smtp smuggling, in part to appease the tools checking for it. smtp errors are 500 "bad syntax", and mention smtp smuggling.
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@ -9,13 +9,24 @@ import (
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)
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func TestDataWrite(t *testing.T) {
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if err := DataWrite(io.Discard, strings.NewReader("bad")); err == nil || !errors.Is(err, errMissingCRLF) {
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t.Fatalf("got err %v, expected errMissingCRLF", err)
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}
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if err := DataWrite(io.Discard, strings.NewReader(".")); err == nil || !errors.Is(err, errMissingCRLF) {
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t.Fatalf("got err %v, expected errMissingCRLF", err)
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checkBad := func(s string, expErr error) {
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t.Helper()
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if err := DataWrite(io.Discard, strings.NewReader(s)); err == nil || !errors.Is(err, expErr) {
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t.Fatalf("got err %v, expected %v", err, expErr)
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}
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}
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checkBad("bad", errMissingCRLF)
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checkBad(".", errMissingCRLF)
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checkBad("bare \r is bad\r\n", ErrCRLF)
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checkBad("bare \n is bad\r\n", ErrCRLF)
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checkBad("\n.\nis bad\r\n", ErrCRLF)
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checkBad("\r.\ris bad\r\n", ErrCRLF)
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checkBad("\r\n.\ris bad\r\n", ErrCRLF)
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checkBad("\r\n.\nis bad\r\n", ErrCRLF)
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checkBad("\n.\ris bad\r\n", ErrCRLF)
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checkBad("\n.\r\nis bad\r\n", ErrCRLF)
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check := func(msg, want string) {
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t.Helper()
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w := &strings.Builder{}
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@ -58,13 +69,15 @@ func TestDataReader(t *testing.T) {
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return wrote, nil
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}
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check := func(data, want string) {
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check := func(data, want string, expErr error) {
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t.Helper()
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s := &strings.Builder{}
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dr := NewDataReader(bufio.NewReader(strings.NewReader(data)))
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if _, err := io.Copy(s, dr); err != nil {
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t.Fatalf("got err %v", err)
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if expErr == nil || !errors.Is(err, expErr) {
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t.Fatalf("got err %v, expected %v", err, expErr)
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}
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} else if got := s.String(); got != want {
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t.Fatalf("got %q, expected %q, for %q", got, want, data)
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}
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@ -72,16 +85,43 @@ func TestDataReader(t *testing.T) {
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s = &strings.Builder{}
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dr = NewDataReader(bufio.NewReader(strings.NewReader(data)))
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if _, err := smallCopy(s, dr); err != nil {
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t.Fatalf("got err %v", err)
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if expErr == nil || !errors.Is(err, expErr) {
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t.Fatalf("got err %v, expected %v", err, expErr)
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}
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} else if got := s.String(); got != want {
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t.Fatalf("got %q, expected %q, for %q", got, want, data)
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}
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}
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check("test\r\n.\r\n", "test\r\n")
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check(".\r\n", "")
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check(".test\r\n.\r\n", "test\r\n") // Unnecessary dot, but valid in SMTP.
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check("..test\r\n.\r\n", ".test\r\n")
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check("test\r\n.\r\n", "test\r\n", nil)
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check(".\r\n", "", nil)
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check(".test\r\n.\r\n", "test\r\n", nil) // Unnecessary dot, but valid in SMTP.
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check("..test\r\n.\r\n", ".test\r\n", nil)
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check("..test\ntest.\n\r\n.\r\n", ".test\ntest.\n\r\n", nil) // Bare newlines are allowed.
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check("..test\ntest\n", "", io.ErrUnexpectedEOF) // Missing end-of-message.
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// Bare \r is rejected.
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check("bare \r is rejected\r\n.\r\n", "", ErrCRLF)
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check("bad:\r.\ris rejected\r\n.\r\n", "", ErrCRLF)
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check("bad:\r.\nis rejected\r\n.\r\n", "", ErrCRLF)
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// Suspicious bare newlines around a dot are rejected.
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check("bad:\n.\nis rejected\r\n.\r\n", "", ErrCRLF)
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check("bad:\n.\r\nis rejected\r\n.\r\n", "", ErrCRLF)
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check("bad:\r\n.\nis rejected\r\n.\r\n", "", ErrCRLF)
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// Suspicious near-smtp-endings at start of message.
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check(".\ris rejected\r\n.\r\n", "", ErrCRLF)
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check(".\nis rejected\r\n.\r\n", "", ErrCRLF)
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check("\n.\ris rejected\r\n.\r\n", "", ErrCRLF)
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check("\r.\ris rejected\r\n.\r\n", "", ErrCRLF)
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check("\n.\nis rejected\r\n.\r\n", "", ErrCRLF)
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check("\r.\nis rejected\r\n.\r\n", "", ErrCRLF)
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check("\r.\r\nis rejected\r\n.\r\n", "", ErrCRLF)
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check("\n.\r\nis rejected\r\n.\r\n", "", ErrCRLF)
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check("\r\n.\ris rejected\r\n.\r\n", "", ErrCRLF)
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check("\r\n.\nis rejected\r\n.\r\n", "", ErrCRLF)
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s := &strings.Builder{}
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dr := NewDataReader(bufio.NewReader(strings.NewReader("no end")))
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