CVE-2020-35776Network attack vector

Service crash via repeated SIP 181 responses

Published Feb 18, 2021 · Updated Aug 4, 2024

Buffer overflow in Sangoma Asterisk 13.38.1, 16.15.1, 17.9.1, and 18.1.1 allows remote attackers to crash the service via SIP 181 responses. The res_pjsip_diversion module repeatedly adds entries to the outbound Supported header without rejecting duplicates or enforcing the entry-array limit. Exploitation requires a registered user to dial a malicious destination that returns enough SIP 181 responses to overflow the array and terminate Asterisk.

CVSS severity6.5
Medium
EPSS probability3.91%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Buffer overflow in Sangoma Asterisk 13.38.1, 16.15.1, 17.9.1, and 18.1.1 allows remote attackers to crash the service via SIP 181 responses. The res_pjsip_diversion module repeatedly adds entries to the outbound Supported header without rejecting duplicates or enforcing the entry-array limit. Exploitation requires a registered user to dial a malicious destination that returns enough SIP 181 responses to overflow the array and terminate Asterisk.

The record

CVE
CVE-2020-35776
Published
Feb 18, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-120, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Feb 18, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

6.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
4.3NIST NVDAV:N/AC:M/Au:N/C:N/I:N/A:P

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-120Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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