CVE-2016-9938
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedAn 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.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceThe chan_sip channel driver in Asterisk incorrectly treats any non-printable ASCII character as whitespace when parsing SIP headers, instead of only stripping spaces and horizontal tabs per RFC 3261. This allows attackers to craft SIP headers like 'Contact\x01:' that bypass authentication when Asterisk sits behind a dialog-unaware SIP proxy—the proxy sees the request as in-dialog (allowing it through), while Asterisk treats it as out-of-dialog (processing it without authentication).
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data= 11.0.0= 11.0.1= 11.0.2= 11.1.0= 11.1.1= 11.1.2= 11.2.0= 11.2.1= 11.2.2= 11.3.0= 11.4.0= 11.5.0= 11.0.0= 11.1.0= 11.2.0= 11.3.0= 11.4.0= 11.5.0= 11.6= 11.6.0CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- Low
- Availability
- None
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Identify Asterisk versionRun 'asterisk -V' or 'core show version' to get the installed Asterisk versionAffected if Version is 11.0.0 through 11.5.0, or is Digium Certified Asterisk 11.0.0 through 11.6.0
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Verify chan_sip is loadedRun 'module show like chan_sip' to check if the chan_sip module is loadedAffected if chan_sip module is loaded and in use (not commented out or replaced by chan_pjsip)
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Check SIP peer/user authentication settingsExamine sip.conf for peers/users with 'secret' or 'auth' defined, or query realtime database if using dynamic peers. Look for entries under [peer] or [user] sections that include authentication credentials.Affected if SIP peers or users are configured with authentication (secret field present) and chan_sip is handling them
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Confirm SIP proxy topologyInspect SIP configuration and network topology to determine if Asterisk receives SIP traffic from an upstream proxy. Check for 'host=' pointing to another SIP server or examine network diagrams.Affected if Asterisk is deployed behind a SIP proxy that may be dialog-unaware, and chan_sip is processing requests that arrive via that proxy
You are affected if you run an affected Asterisk version (11.0.0-11.5.0 or certified 11.0.0-11.6.0), use chan_sip module, and have SIP peers with authentication configured, especially if Asterisk sits behind a SIP proxy.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
From vendor dataIf using chan_sip with an upstream SIP proxy, upgrade to the patched versions (11.25.1, 13.13.1, 14.2.1, 11.6-cert16, or 13.8-cert4) or migrate to chan_pjsip. Alternatively, ensure the proxy is dialog-aware or handle authentication before the proxy.
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- Implementation4.0 h
- Testing3.0 h
- Review / QA2.0 h
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Free · runs locallyCheck whether your project pulls in CVE-2016-9938 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2016-9938 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
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