Merge branch 'master' of git://git.exim.org/exim

[exim.git] / src / src / smtp_in.c

diff --git a/src/src/smtp_in.c b/src/src/smtp_in.c
index 2ef6977024d543a459be6d72fc5be17ba138922a..38c7afcf6fbd1bdad10078f6904e71777aebfdf2 100644 (file)
--- a/src/src/smtp_in.c
+++ b/src/src/smtp_in.c
@@ -3844,6 +3844,32 @@ while (done <= 0)
     toomany = FALSE;
     cmd_list[CMD_LIST_STARTTLS].is_mail_cmd = FALSE;
 
+    /* There's an attack where more data is read in past the STARTTLS command
+    before TLS is negotiated, then assumed to be part of the secure session
+    when used afterwards; we use segregated input buffers, so are not
+    vulnerable, but we want to note when it happens and, for sheer paranoia,
+    ensure that the buffer is "wiped".
+    Pipelining sync checks will normally have protected us too, unless disabled
+    by configuration. */
+
+    if (receive_smtp_buffered())
+      {
+      DEBUG(D_any)
+        debug_printf("Non-empty input buffer after STARTTLS; naive attack?");
+      if (tls_active < 0)
+        smtp_inend = smtp_inptr = smtp_inbuffer;
+      /* and if TLS is already active, tls_server_start() should fail */
+      }
+
+    /* There is nothing we value in the input buffer and if TLS is succesfully
+    negotiated, we won't use this buffer again; if TLS fails, we'll just read
+    fresh content into it.  The buffer contains arbitrary content from an
+    untrusted remote source; eg: NOOP <shellcode>\r\nSTARTTLS\r\n
+    It seems safest to just wipe away the content rather than leave it as a
+    target to jump to. */
+
+    memset(smtp_inbuffer, 0, in_buffer_size);
+
     /* Attempt to start up a TLS session, and if successful, discard all
     knowledge that was obtained previously. At least, that's what the RFC says,
     and that's what happens by default. However, in order to work round YAEB,