Auth bypass in Digium Asterisk
CVE-2016-9938
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.
Published · last modified .
CVSS v3 metric
CVSS v3 base score 5.3 (Medium). Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N.
EPSS exploit prediction
EPSS: 0.034 (88.5th percentile), scored .
Low probability of exploitation in the next 30 days, but still tracked. 89th percentile — 88.5% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.034 · newest: 0.034 · change: 0.000
Affected products
- Digium Asterisk — versions 11.0.0, 11.0.1, 11.0.2
- Digium Certified Asterisk — versions 11.0.0, 11.1.0, 11.2.0
Weakness classification (CWE)
Public proof-of-concept exploits
References
- downloads.asterisk.org/pub/security/AST-2016-009.html (Mitigation, Vendor Advisory)
- www.securityfocus.com/bid/94789 (VDB Entry, Third Party Advisory, vdb-entry)
- www.securitytracker.com/id/1037408 (vdb-entry)
Frequently asked questions
- What is CVE-2016-9938?
- CVE-2016-9938 is a medium-severity vulnerability in Digium Asterisk, classified under Improper Authorization. CVSS score: 5.3/10. Published 2016-12-12.
- How severe is CVE-2016-9938?
- Medium severity. CVSS v3 base score is 5.3 out of 10.
- Is CVE-2016-9938 known to be exploited?
- 1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.