CVE-2021-26713Network attack vector

Authenticated crash via signed packet-size comparison

Published Feb 19, 2021 · Updated Aug 3, 2024

Stack overflow in Sangoma Asterisk before 16.16.1, 17.9.2, or 18.2.1 allows remote authenticated users to crash it via WebRTC. The res_rtp_asterisk.c module compares packet sizes with mismatched signedness, allowing rapid hold/unhold requests to overflow a stack buffer. An authenticated WebRTC session is required; the same crash affects Certified Asterisk before 16.8-cert6 and interrupts call processing.

CVSS severity6.5
Medium
EPSS probability1.85%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Stack overflow in Sangoma Asterisk before 16.16.1, 17.9.2, or 18.2.1 allows remote authenticated users to crash it via WebRTC. The res_rtp_asterisk.c module compares packet sizes with mismatched signedness, allowing rapid hold/unhold requests to overflow a stack buffer. An authenticated WebRTC session is required; the same crash affects Certified Asterisk before 16.8-cert6 and interrupts call processing.

The record

CVE
CVE-2021-26713
Published
Feb 19, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-787, T1499.004
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Feb 19, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 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 privilegesauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

4.0NIST NVDAV:N/AC:L/Au:S/C:N/I:N/A:P
6.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

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
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-787Out-of-bounds Write
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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