CVE-2021-34790Public exploitNetwork attack vector

Unauthorized connection opening via insufficient SIP validation

Published Oct 27, 2021 · Updated Nov 7, 2024

SIP ALG bypass in Cisco ASA Software allows unauthenticated remote attackers to open unauthorized connections using crafted SIP traffic. The default-enabled SIP ALG insufficiently validates traffic and interprets attacker-controlled SIP data when creating NAT state for a host behind the appliance. A victim behind the appliance must visit attacker-controlled web content; successful exploitation opens a firewall pinhole to a chosen internal service.

CVSS severity4.7
Medium
EPSS probability1.14%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

SIP ALG bypass in Cisco ASA Software allows unauthenticated remote attackers to open unauthorized connections using crafted SIP traffic. The default-enabled SIP ALG insufficiently validates traffic and interprets attacker-controlled SIP data when creating NAT state for a host behind the appliance. A victim behind the appliance must visit attacker-controlled web content; successful exploitation opens a firewall pinhole to a chosen internal service.

The record

CVE
CVE-2021-34790
Published
Oct 27, 2021
Updated
Nov 7, 2024
Vendor
ClamAV
Product
Cisco Adaptive Security Appliance (ASA) Software
Classifications
CWE-358, T1189
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 27, 2021CVE publishedPublication date reported by the CVE source.
  2. Nov 7, 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?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=n/a

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

ClamAV · Cisco Adaptive Security Appliance (ASA) Softwareversion=n/a

Published CVSS scores

4.7CiscoCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:N/I:L/A:N

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.

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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 exploitPublished

Weakness, pattern, technique

CWE-358Improperly Implemented Security Check for Standard
T1189Drive-by Compromise

Public exploit references

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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