CVE-2021-26906

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.

Published: 2021-02-18 Last update: 2026-06-16 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-26906 is rated Moderate Risk (54.4/100): CVSS Medium severity, with medium exploitation likelihood (EPSS 2.55%). EPSS rose +1.74% over the last day, indicating growing attacker interest. Review affected assets and schedule remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2021-26906

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 0.81% 2.55% +1.74%
2 2026-01-15 0.51% 0.81% +0.30%
3 2025-11-21 — 0.51% —

Full EPSS history (17 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-26906

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
5.9 3.1 MEDIUM
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:H)
Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 2.2 3.6 [email protected]
4.3 2.0 MEDIUM
AV:N/AC:M/Au:N/C:N/I:N/A:P Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:M)
Exploitation needs some favorable conditions, but not exceptional ones.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:N)
No confidentiality impact.
Integrity impact (I:N)
No integrity impact.
Availability impact (A:P)
Partial availability impact.
 8.6 2.9 [email protected]

Weakness enumeration for CVE-2021-26906

OS Trackers for CVE-2021-26906

vendor priority summary link
alpine medium CVE-2021-26906: 1 source package rows (asterisk); 41 state rows across 10 repos (3.10-main, 3.11-main, 3.12-main, 3.17-main, 3.18-main, 3.19-main, 3.20-main, 3.21-main, 3.22-main, edge-main); fixed 8, open 33. https://security.alpinelinux.org/vuln/CVE-2021-26906
debian not yet assigned CVE-2021-26906 not yet assigned priority: Debian including 1 source packages (asterisk), 2 status rows across 2 suites (bullseye, sid): resolved 2. https://security-tracker.debian.org/tracker/CVE-2021-26906
gentoo high CVE-2021-26906: 1 GLSA(s) (202412-03), 1 atom(s) (net-misc/asterisk); latest impact high. https://bugs.gentoo.org/buglist.cgi?quicksearch=CVE-2021-26906
ubuntu medium CVE-2021-26906 medium priority: Ubuntu including 1 source packages (asterisk), 6 status rows across 6 suites (bionic, focal, groovy, trusty, upstream, xenial): not-affected 4, DNE 1, needs-triage 1. https://ubuntu.com/security/CVE-2021-26906

Affected software / configurations for CVE-2021-26906

Vendor Product Version Raw CPE
digium asterisk >= 13.0.0, < 13.38.2 cpe:2.3:a:digium:asterisk:*:*:*:*:*:*:*:*
digium asterisk >= 16.0.0, < 16.16.1 cpe:2.3:a:digium:asterisk:*:*:*:*:*:*:*:*
digium asterisk >= 17.0.0, < 17.9.2 cpe:2.3:a:digium:asterisk:*:*:*:*:*:*:*:*
digium asterisk >= 18.0, < 18.2.1 cpe:2.3:a:digium:asterisk:*:*:*:*:*:*:*:*
digium certified_asterisk 16.8 cpe:2.3:a:digium:certified_asterisk:16.8:-:*:*:*:*:*:*
digium certified_asterisk 16.8 cpe:2.3:a:digium:certified_asterisk:16.8:cert1-rc1:*:*:*:*:*:*
digium certified_asterisk 16.8 cpe:2.3:a:digium:certified_asterisk:16.8:cert1-rc2:*:*:*:*:*:*
digium certified_asterisk 16.8 cpe:2.3:a:digium:certified_asterisk:16.8:cert1-rc3:*:*:*:*:*:*
digium certified_asterisk 16.8 cpe:2.3:a:digium:certified_asterisk:16.8:cert1-rc4:*:*:*:*:*:*
digium certified_asterisk 16.8 cpe:2.3:a:digium:certified_asterisk:16.8:cert2:*:*:*:*:*:*
digium certified_asterisk 16.8 cpe:2.3:a:digium:certified_asterisk:16.8:cert3:*:*:*:*:*:*
digium certified_asterisk 16.8 cpe:2.3:a:digium:certified_asterisk:16.8:cert4:*:*:*:*:*:*
digium certified_asterisk 16.8 cpe:2.3:a:digium:certified_asterisk:16.8:cert4-rc1:*:*:*:*:*:*
digium certified_asterisk 16.8 cpe:2.3:a:digium:certified_asterisk:16.8:cert4-rc2:*:*:*:*:*:*
digium certified_asterisk 16.8 cpe:2.3:a:digium:certified_asterisk:16.8:cert4-rc3:*:*:*:*:*:*
digium certified_asterisk 16.8 cpe:2.3:a:digium:certified_asterisk:16.8:cert4-rc4:*:*:*:*:*:*
digium certified_asterisk 16.8 cpe:2.3:a:digium:certified_asterisk:16.8:cert5:*:*:*:*:*:*

References for CVE-2021-26906

cvelogic Threat Intelligence