CVE-2016-9938 Auth bypass in n/a
Attackers can bypass authentication and process unauthorized calls when Asterisk uses the chan_sip driver behind a non-dialog-aware SIP proxy.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2016-9938?
CVE-2016-9938 is a medium-severity authentication bypass vulnerability in Digium Asterisk, published on 12 Dec 2016. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
An issue was discovered in Asterisk Open Source 11.x before 11.25.1, 13.x before 13.13.1, and 14.x before 14.2.1 and Certified Asterisk 11.x before 11.6-cert16 and 13.x before 13.8-cert4. 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.
Weakness: CWE-285
Which versions are affected by CVE-2016-9938?
It affects 2 products.
Products include Digium Asterisk, Digium Certified Asterisk.
How do I fix CVE-2016-9938?
Upgrade to a fixed version.
Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.
Is CVE-2016-9938 being exploited?
There is no known exploitation of CVE-2016-9938 in the wild and no public exploit code.
Other vulnerabilities in Digium Asterisk
Sources
Also known as DEBIAN-CVE-2016-9938, GHSA-4h4c-qgxg-p3qv, UBUNTU-CVE-2016-9938.