FreeBSD VuXML: Documenting security issues in FreeBSD and the FreeBSD Ports Collection

asterisk -- Authentication Bypass

Affected packages
asterisk11 < 11.25.1
asterisk13 < 13.13.1


VuXML ID c0b13887-be44-11e6-b04f-001999f8d30b
Discovery 2016-11-28
Entry 2016-12-09

The Asterisk project reports:

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 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.