[SR-Users] Asterisk Security Advisory (AST-2016-009)

[Matthew Jordan]

Hey all -

The Asterisk project just released a security advisory for a security
vulnerability in which Asterisk using chan_sip with a proxy can allow for
unauthenticated calls. This affects all supported versions of Asterisk (11,
13, 14). Since that may be relevant to those on this mailing list who are
not also on the asterisk-users mailing list, I thought it prudent to
mention it here as well.

A description of the vulnerability follows:

    Description  The chan_sip channel driver has a liberal definition for
                 whitespace when attempting to strip the content between a
                 SIP header name and a colon character. Rather than
                 following RFC 3261 and stripping only spaces and horizontal
                 tabs, Asterisk treats any non-printable ASCII character as
                 if it were whitespace. This means that headers such as

                 Contact\x01:

                 will be seen as a valid Contact header.

                 This mostly does not pose a problem until Asterisk is
                 placed in tandem with an authenticating SIP proxy. In such
                 a case, a crafty combination of valid and invalid To
                 headers can cause a proxy to allow an INVITE request into
                 Asterisk without authentication since it believes the
                 request is an in-dialog request. However, because of the
                 bug described above, the request will look like an
                 out-of-dialog request to Asterisk. Asterisk will then
                 process the request as a new call. The result is that
                 Asterisk can process calls from unvetted sources without
                 any authentication.

                 If you do not use a proxy for authentication, then this
                 issue does not affect you.

                 If your proxy is dialog-aware (meaning that the proxy keeps
                 track of what dialogs are currently valid), then this issue
                 does not affect you.

                 If you use chan_pjsip instead of chan_sip, then this issue
                 does not affect you.


The announcement can be seen here:

http://lists.digium.com/pipermail/asterisk-announce/2016-December/000662.html

Thanks again to Walter Doekes for reporting the vulnerability and providing
the patch to fix it.

Matt

-- 
Matthew Jordan
Digium, Inc. | CTO
445 Jan Davis Drive NW - Huntsville, AL 35806 - USA
Check us out at: http://digium.com & http://asterisk.org
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