How severe is CVE-2021-34705?

CVE-2021-34705 has a CVSS 3.x base score of 5.3, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity low, and availability none.

Is CVE-2021-34705 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (58th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-34705?

CVE-2021-34705 primarily affects Cisco Ios. In total, 1721 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-34705?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2021-34705 published?

CVE-2021-34705 was published on 2021-09-23 and last updated on 2026-06-17.

CVE-2021-34705

CVE-2021-34705 is a medium-severity vulnerability in Cisco Ios with a CVSS 3.x base score of 5.3. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-232.

Key facts

Severity: Medium (CVSS 3.x base score 5.3)
CVSS v2: 4.3
EPSS exploit prediction: 1% (58th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-232
Affected product: Cisco Ios
Published: 2021-09-23
Last modified: 2026-06-17

Description

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.

Frequently asked questions

What is CVE-2021-34705?: 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.
How severe is CVE-2021-34705?: CVE-2021-34705 has a CVSS 3.x base score of 5.3, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity low, and availability none.
Is CVE-2021-34705 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (58th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-34705?: CVE-2021-34705 primarily affects Cisco Ios. In total, 1721 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-34705?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2021-34705 published?: CVE-2021-34705 was published on 2021-09-23 and last updated on 2026-06-17.

References

https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-fxo-pattern-bypass-jUXgygYv

Affected products (1721)

cpe:2.3:o:cisco:ios:12.3\(7\)xm:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:12.3\(7\)xr:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:12.3\(7\)xr1:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:12.3\(7\)xr2:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:12.3\(7\)xr3:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:12.3\(7\)xr4:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:12.3\(7\)xr5:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:12.3\(7\)xr6:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:12.3\(7\)xr7:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:12.3\(8\)ja2:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:12.3\(8\)jea1:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:12.3\(8\)jea2:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:12.3\(8\)jea3:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:12.3\(8\)jeb:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:12.3\(8\)jeb1:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:12.3\(8\)jec3:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:12.3\(8\)jed1:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:12.3\(8\)jee:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:12.3\(8\)jk:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:12.3\(8\)jk1:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:12.3\(8\)t:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:12.3\(8\)t0a:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:12.3\(8\)t1:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:12.3\(8\)t2:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:12.3\(8\)t3:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:12.3\(8\)t4:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:12.3\(8\)t5:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:12.3\(8\)t6:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:12.3\(8\)t7:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:12.3\(8\)t8:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:12.3\(8\)t9:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:12.3\(8\)t10:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:12.3\(8\)t11:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:12.3\(8\)xu:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:12.3\(8\)xu1:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:12.3\(8\)xu2:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:12.3\(8\)xu3:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:12.3\(8\)xu4:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:12.3\(8\)xu5:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios:12.3\(8\)xw:*:*:*:*:*:*:*

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