CVE-2016-9938

What it is

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.

At a glance

Exploitability

Can be exploited over the network without logging in. Limited direct impact.

Exploit odds

3.4% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2016-12-12 21:59 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-06-17 00:56 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 3.4% in the next 30 days (EPSS).
• Severity: 5.3 MEDIUM (CVSS).
• Fix: a patch or advisory is linked.

Details

Published

2016-12-12 21:59 UTC

Last modified

2026-06-17 00:56 UTC

Exploit probability

3.4% · EPSS, next 30 days

Weakness

CWE-285

Record status

Modified

Affected

• Digium Asterisk 11.0.0
• Digium Asterisk 11.0.1
• Digium Asterisk 11.0.2
• Digium Asterisk 11.1.0
• Digium Asterisk 11.1.1
• Digium Asterisk 11.1.2
• Digium Asterisk 11.2.0
• Digium Asterisk 11.2.1

Attack profile CVSS 3.0 · 5.3

Attack vector

Network

Complexity

Low

Privileges needed

None

User interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

Low

Availability

None

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2016-9938.md and follow it. Check whether this project is affected by CVE-2016-9938. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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