HOME VULNERABILITIESCVE-2021-26906

MEDIUM

CVE-2021-26906

CWE-404Published: February 18, 2021· Updated: Jun 17, 2026

5.9

CVSS v3.1

Official Description

An issue was discovered in res_pjsip_session.c in Digium Asterisk through 13.38.1; 14.x, 15.x, and 16.x through 16.16.0; 17.x through 17.9.1; and 18.x through 18.2.0, and Certified Asterisk through 16.8-cert5. An SDP negotiation vulnerability in PJSIP allows a remote server to potentially crash Asterisk by sending specific SIP responses that cause an SDP negotiation failure.

Technical Analysis

CVE-2021-26906 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.

The vulnerability requires no privileges and no user interaction, making it a prime target for automated exploitation campaigns and worm-like propagation.

A successful exploit results in availability disruption (denial of service), with a CVSS base score of 5.9.

CVSS v3.1 Vector Breakdown

Exploitability

Attack VectorNetwork

Attack ComplexityHigh

Privileges Req.None

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityNone

IntegrityNone

AvailabilityHigh

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

Affected Vendors & Products

digium2 product(s)

asteriskcertified asterisk

Source: NVD CPE · 2 total CPE entries

Exploit & PoC Resources

NO KNOWN EXPLOITNo public exploit confirmed at this time

Offensive Security exploit database

GitHub PoC Search

Community PoC repositories

Rapid7 / Metasploit

Metasploit module search

Security advisories & exploits

Official NIST entry

CVE Program entry

External links open in a new tab. Always verify in a controlled environment before use.

Official Patches & Advisories

PATCHhttp://seclists.org/fulldisclosure/2021/Feb/61

PATCHhttps://issues.asterisk.org/jira/browse/ASTERISK-29196

PATCHhttp://seclists.org/fulldisclosure/2021/Feb/61

PATCHhttps://issues.asterisk.org/jira/browse/ASTERISK-29196

ADVISORYhttp://packetstormsecurity.com/files/161477/Asterisk-Project-Security-Advisory-AST-2021-005.html

ADVISORYhttps://downloads.asterisk.org/pub/security/

ADVISORYhttps://downloads.asterisk.org/pub/security/AST-2021-005.html

ADVISORYhttp://packetstormsecurity.com/files/161477/Asterisk-Project-Security-Advisory-AST-2021-005.html

ADVISORYhttps://downloads.asterisk.org/pub/security/

ADVISORYhttps://downloads.asterisk.org/pub/security/AST-2021-005.html

All References (10)

→

http://packetstormsecurity.com/files/161477/Asterisk-Project-Security-Advisory-AST-2021-005.htmlThird Party Advisory

→

http://seclists.org/fulldisclosure/2021/Feb/61Mailing List · Patch · Third Party Advisory

→

https://downloads.asterisk.org/pub/security/Vendor Advisory

→

https://downloads.asterisk.org/pub/security/AST-2021-005.htmlVendor Advisory

→

https://issues.asterisk.org/jira/browse/ASTERISK-29196Issue Tracking · Patch · Vendor Advisory

→

http://packetstormsecurity.com/files/161477/Asterisk-Project-Security-Advisory-AST-2021-005.htmlThird Party Advisory

→

http://seclists.org/fulldisclosure/2021/Feb/61Mailing List · Patch · Third Party Advisory

→

https://downloads.asterisk.org/pub/security/Vendor Advisory

→

https://downloads.asterisk.org/pub/security/AST-2021-005.htmlVendor Advisory

→

https://issues.asterisk.org/jira/browse/ASTERISK-29196Issue Tracking · Patch · Vendor Advisory

Quick Facts

CVE IDCVE-2021-26906

CVSS Score5.9 / 10

SeverityMEDIUM

WeaknessCWE-404

CISA KEVNo

Affected1 vendor(s)

PublishedFeb 18, 2021

Related CVEs (CWE-404)

Recommended Actions

→Apply vendor patches immediately
→Monitor CVE-2021-26906 in threat intel feeds
→Review IDS/IPS signatures for exploitation attempts

Data sourced from NVD (NIST), CISA KEV, and EPSS (FIRST). Analysis generated by CTIWATCH.COM. CVE data is provided under the NVD usage policy.

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