Security features bypass in Cisco IOS and IOS XE Software

Published: 2021-09-23
Risk Medium
Patch available YES
Number of vulnerabilities 1
CVE-ID CVE-2021-34705
Exploitation vector Network
Public exploit N/A
Vulnerable software
Cisco IOS
Operating systems & Components / Operating system

Cisco IOS XE
Operating systems & Components / Operating system

Vendor Cisco Systems, Inc

Security Bulletin

This security bulletin contains one medium risk vulnerability.

1) Security features bypass

EUVDB-ID: #VU56841

Risk: Medium

CVSSv3.1: 4.6 [CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N/E:U/RL:O/RC:C]

CVE-ID: CVE-2021-34705

CWE-ID: CWE-254 - Security Features

Exploit availability: No


The vulnerability allows a remote attacker to compromise the target system.

The vulnerability exists due to insufficient validation of dial strings at Foreign Exchange Office (FXO) interfaces in the Voice Telephony Service Provider (VTSP) service. A remote attacker can send a specially crafted dial string and conduct toll fraud, resulting in unexpected financial impact to affected customers.


Install updates from vendor's website.

Vulnerable software versions

Cisco IOS: 15.1(4)M

Cisco IOS XE: 15.1(4)M

CPE2.3 External links

Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote non-authenticated attacker via the Internet.

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability.