How severe is CVE-2021-26906?

CVE-2021-26906 has a CVSS 3.x base score of 5.9, rated medium severity. It is exploitable over network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2021-26906 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 3% (83rd percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-26906?

CVE-2021-26906 primarily affects Digium Asterisk. In total, 14 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-26906?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2021-26906 published?

CVE-2021-26906 was published on 2021-02-18 and last updated on 2026-06-17.

CVE-2021-26906

CVE-2021-26906 is a medium-severity vulnerability in Digium Asterisk with a CVSS 3.x base score of 5.9. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-404.

Key facts

Severity: Medium (CVSS 3.x base score 5.9)
CVSS v2: 4.3
EPSS exploit prediction: 3% (83rd percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-404
Affected product: Digium Asterisk
Published: 2021-02-18
Last modified: 2026-06-17

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.

Frequently asked questions

What is 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.
How severe is CVE-2021-26906?: CVE-2021-26906 has a CVSS 3.x base score of 5.9, rated medium severity. It is exploitable over network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2021-26906 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 3% (83rd percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-26906?: CVE-2021-26906 primarily affects Digium Asterisk. In total, 14 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-26906?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2021-26906 published?: CVE-2021-26906 was published on 2021-02-18 and last updated on 2026-06-17.

References

Affected products (14)

cpe:2.3:a:digium:asterisk:*:*:*:*:*:*:*:*
cpe:2.3:a:digium:certified_asterisk:16.8:-:*:*:*:*:*:*
cpe:2.3:a:digium:certified_asterisk:16.8:cert1-rc1:*:*:*:*:*:*
cpe:2.3:a:digium:certified_asterisk:16.8:cert1-rc2:*:*:*:*:*:*
cpe:2.3:a:digium:certified_asterisk:16.8:cert1-rc3:*:*:*:*:*:*
cpe:2.3:a:digium:certified_asterisk:16.8:cert1-rc4:*:*:*:*:*:*
cpe:2.3:a:digium:certified_asterisk:16.8:cert2:*:*:*:*:*:*
cpe:2.3:a:digium:certified_asterisk:16.8:cert3:*:*:*:*:*:*
cpe:2.3:a:digium:certified_asterisk:16.8:cert4:*:*:*:*:*:*
cpe:2.3:a:digium:certified_asterisk:16.8:cert4-rc1:*:*:*:*:*:*
cpe:2.3:a:digium:certified_asterisk:16.8:cert4-rc2:*:*:*:*:*:*
cpe:2.3:a:digium:certified_asterisk:16.8:cert4-rc3:*:*:*:*:*:*
cpe:2.3:a:digium:certified_asterisk:16.8:cert4-rc4:*:*:*:*:*:*
cpe:2.3:a:digium:certified_asterisk:16.8:cert5:*:*:*:*:*:*

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