[SECURITY ADVISORY] curl - SASL password overflow via integer overflow

[Daniel Stenberg]

SASL password overflow via integer overflow
===========================================

Project curl Security Advisory, October 31st 2018 -
[Permalink](https://curl.haxx.se/docs/CVE-2018-16839.html)

VULNERABILITY
-------------

libcurl contains a buffer overrun in the SASL authentication code.

The internal function `Curl_auth_create_plain_message` fails to correctly
verify that the passed in lengths for name and password aren't too long, then
calculates a buffer size to allocate.

On systems with a 32 bit `size_t`, the math to calculate the buffer size
triggers an integer overflow when the user name length exceeds 2GB (2^31
bytes). This integer overflow usually causes a very small buffer to actually
get allocated instead of the intended very huge one, making the use of that
buffer end up in a heap buffer overflow.

(This bug is very similar to
[CVE-2017-14618](https://curl.haxx.se/docs/CVE-2018-14618.html).)

We are not aware of any exploit of this flaw.

INFO
----

The affected function can only be invoked when using POP3(S), IMAP(S) or
SMTP(S).

This bug was introduced in [commit
c56f9797e7feb7c2dc](https://github.com/curl/curl/commit/c56f9797e7feb7c2dc),
August 2013.

The Common Vulnerabilities and Exposures (CVE) project has assigned the name
CVE-2018-16839 to this issue.

CWE-131: Incorrect Calculation of Buffer Size

Severity: 3.2 (Low)

AFFECTED VERSIONS
-----------------

This issue is only present on 32 bit systems. It also requires the username
field to use more than 2GB of memory, which should be rare.

- Affected versions: libcurl 7.33.0 to and including 7.61.1
- Not affected versions: libcurl < 7.33.0 and >= 7.62.0

curl is used by many applications, but not always advertised as such.

THE SOLUTION
------------

In libcurl version 7.62.0, the integer overflow is avoided. An error will be
returned if a too long user name is attempted.

A [patch for
CVE-2018-16839](https://github.com/curl/curl/commit/f3a24d7916b9173c69a3e0ee790102993833d6c5)
is available.

RECOMMENDATIONS
---------------

We suggest you take one of the following actions immediately, in order of
preference:

A - Upgrade curl to version 7.62.0

B - Apply the patch to your version and rebuild

C - Put length restrictions on the username field you can pass to libcurl

TIME LINE
---------

It was reported to the curl project on September 6, 2018. We contacted
***@openwall on October 22.

curl 7.62.0 was released on October 31 2018, coordinated with the publication
of this advisory.

CREDITS
-------

Reported by Harry Sintonen. Patch by Daniel Stenberg.

Thanks a lot!