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smtp: avoid risk of buffer overflow in strtol

If the incoming len 5, but the buffer does not have a termination
after 5 bytes, the strtol() call may keep reading through the line
buffer until is exceeds its boundary. Fix by ensuring that we are
using a bounded read with a temporary buffer on the stack.

Bug: https://curl.haxx.se/docs/CVE-2019-3823.html
Reported-by: Brian Carpenter (Geeknik Labs)
CVE-2019-3823
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danielgustafsson authored and bagder committed Jan 18, 2019
1 parent 50c9484 commit 39df4073e5413fcdbb5a38da0c1ce6f1c0ceb484
Showing with 6 additions and 2 deletions.
  1. +6 −2 lib/smtp.c
@@ -5,7 +5,7 @@
* | (__| |_| | _ <| |___
* \___|\___/|_| \_\_____|
*
* Copyright (C) 1998 - 2018, Daniel Stenberg, <daniel@haxx.se>, et al.
* Copyright (C) 1998 - 2019, Daniel Stenberg, <daniel@haxx.se>, et al.
*
* This software is licensed as described in the file COPYING, which
* you should have received as part of this distribution. The terms
@@ -207,8 +207,12 @@ static bool smtp_endofresp(struct connectdata *conn, char *line, size_t len,
Section 4. Examples of RFC-4954 but some e-mail servers ignore this and
only send the response code instead as per Section 4.2. */
if(line[3] == ' ' || len == 5) {
char tmpline[6];

result = TRUE;
*resp = curlx_sltosi(strtol(line, NULL, 10));
memset(tmpline, '\0', sizeof(tmpline));
memcpy(tmpline, line, (len == 5 ? 5 : 3));
*resp = curlx_sltosi(strtol(tmpline, NULL, 10));

/* Make sure real server never sends internal value */
if(*resp == 1)

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