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FedoraOperating system · Fedoraproject

CVE-2020-28242

MEDIUM · 6.5 CVSS v3.1 Published 2020-11-06
Fix available
A fix is available. Upgrade to 13.37.1 / 16.14.1 or later.
See remediation →
71/100
Remediation priority · Elevated
Remotely reachable Zero-click

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 · unedited
An issue was discovered in Asterisk Open Source 13.x before 13.37.1, 16.x before 16.14.1, 17.x before 17.8.1, and 18.x before 18.0.1 and Certified Asterisk before 16.8-cert5. If Asterisk is challenged on an outbound INVITE and the nonce is changed in each response, Asterisk will continually send INVITEs in a loop. This causes Asterisk to consume more and more memory since the transaction will never terminate (even if the call is hung up), ultimately leading to a restart or shutdown of Asterisk. Outbound authentication must be configured on the endpoint for this to occur.

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 confidence

A denial-of-service vulnerability in Asterisk allows an authentication loop when a server changes the nonce in each 401/407 challenge response to an outbound INVITE. Asterisk continually resends INVITEs without termination, causing unbounded memory consumption that leads to process failure and restart.

MitigationUpgrade Asterisk to version 13.37.1, 16.14.1, 17.8.1, 18.0.1, or Certified Asterisk 16.8-cert5 or later. Consider rate limiting or monitoring for repeated authentication attempts as a defensive measure.

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
FedoraOperating system
Affected:= 33
Debian LinuxOperating system
Affected:= 9.0
Certified AsteriskApplication
Affected:<= 16.8.0
AsteriskApplication
Affected:>= 13.0, < 13.37.1>= 16.0, < 16.14.1>= 17.0, < 17.8.1>= 18.0, < 18.0.1

CVSS 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
Low
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

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 checks

Work through these to decide whether this CVE applies to you.

  1. Determine installed Asterisk version
    Run `asterisk -V` or `asterisk --version` to obtain the exact version number
    Affected if The version falls within any of the affected ranges: Asterisk Certified <= 16.8.0; Sangoma Asterisk 13.0 to 13.37.0, 16.0 to 16.14.0, 17.0 to 17.8.0, or 18.0.0; or running on Fedora 33 or Debian 9.0 with Asterisk installed
  2. Identify if outbound INVITE with authentication is configured
    Examine Asterisk configuration files (typically in /etc/asterisk/) for PJSIP or SIP endpoints configured with outbound authentication, looking for entries under pjsip.conf or sip.conf that include auth= or outbound_auth= statements
    Affected if Any PJSIP or SIP trunk/peer is configured with outbound authentication credentials for INVITE requests
  3. Check for active SIP trunk or outbound registration
    Review Asterisk configuration for sip.conf (peers/trunks) or pjsip.conf (endpoints/auth) that establish outbound calls to remote SIP servers, particularly any that require 401 or 407 authentication challenges
    Affected if Asterisk is configured to place outbound INVITE requests to remote SIP servers that respond with authentication challenges
  4. Monitor for repeated INVITE retransmissions
    Use `sip show peers` or `pjsip show contacts` CLI commands to observe if the same endpoints are being repeatedly contacted, or check Asterisk logs for patterns of INVITE retries without successful authentication
    Affected if Logs or CLI show continuous INVITE retransmission attempts to the same remote hosts, indicating the authentication loop is occurring

A user is affected if Asterisk is installed with a version matching the affected ranges AND the system is configured to send outbound INVITE requests that trigger 401/407 authentication challenges from remote SIP servers.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

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 data
Upgrade available Upgrade to 13.37.1 / 16.14.1 / 17.8.1 or later
Fixed in 13.37.116.14.117.8.1
Interim mitigation

Upgrade Asterisk to version 13.37.1, 16.14.1, 17.8.1, 18.0.1, or Certified Asterisk 16.8-cert5 or later. Consider rate limiting or monitoring for repeated authentication attempts as a defensive measure.

Fix this in Fedora Scoped from the published advisory
  • Consultation2.0 h
  • Implementation2.0 h
  • Testing3.0 h
  • Review / QA2.0 h
9.0 hours of engineering $1,570
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2020-28242 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • 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
  • No spam, self-promotion, credentials, or personal data