CVE-2021-34705

What it is

A vulnerability in the Voice Telephony Service Provider (VTSP) service of Cisco IOS Software and Cisco IOS XE Software could allow an unauthenticated, remote attacker to bypass configured destination patterns and dial arbitrary numbers. This vulnerability is due to insufficient validation of dial strings at Foreign Exchange Office (FXO) interfaces. An attacker could exploit this vulnerability by sending a malformed dial string to an affected device via either the ISDN protocol or SIP. A successful exploit could allow the attacker to conduct toll fraud, resulting in unexpected financial impact to affected customers.

At a glance

Exploitability

Can be exploited over the network without logging in. Limited direct impact.

Exploit odds

1.0% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2021-09-23 03:15 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-06-17 03:56 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 1.0% in the next 30 days (EPSS).
• Severity: 5.3 MEDIUM (CVSS).
• Fix: a patch or advisory is linked.

Details

Published

2021-09-23 03:15 UTC

Last modified

2026-06-17 03:56 UTC

Exploit probability

1.0% · EPSS, next 30 days

Weakness

CWE-232

Record status

Analyzed

Affected

• Cisco iOS 12.3\(7\)xm
• Cisco iOS 12.3\(7\)xr
• Cisco iOS 12.3\(7\)xr1
• Cisco iOS 12.3\(7\)xr2
• Cisco iOS 12.3\(7\)xr3
• Cisco iOS 12.3\(7\)xr4
• Cisco iOS 12.3\(7\)xr5
• Cisco iOS 12.3\(7\)xr6

Attack profile CVSS 3.1 · 5.3

Attack vector

Network

Complexity

Low

Privileges needed

None

User interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

Low

Availability

None

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2021-34705.md and follow it. Check whether this project is affected by CVE-2021-34705. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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