CVE-2021-34705 | Cisco IOS and IOS XE Software FXO Interface Destination Pattern Bypass Vulnerability

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.

Published: 2021-09-23 Last update: 2025-10-30 Assigner: [email protected] Source: [email protected]
NVD Status：Analyzed，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-34705 is rated Moderate Risk (45/100): CVSS Medium severity, with medium exploitation likelihood (EPSS 0.55%). Review affected assets and schedule remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2021-34705

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2025-12-28 0.34% 0.55% +0.21%
2 2025-12-27 0.55% 0.34% -0.21%
3 2025-11-21 — 0.55% —

Full EPSS history (16 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-34705

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
5.3 3.1 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:L)
Attackers could change some data, but it’s limited—not everything goes.
Availability (A:N)
Service keeps running; no real outage angle.
 3.9 1.4 [email protected]
5.3 3.1 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:L)
Attackers could change some data, but it’s limited—not everything goes.
Availability (A:N)
Service keeps running; no real outage angle.
 3.9 1.4 [email protected]
4.3 2.0 MEDIUM
AV:N/AC:M/Au:N/C:N/I:P/A:N Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:M)
Exploitation needs some favorable conditions, but not exceptional ones.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:N)
No confidentiality impact.
Integrity impact (I:P)
Partial integrity impact.
Availability impact (A:N)
No availability impact.
 8.6 2.9 [email protected]

Weakness enumeration for CVE-2021-34705

Affected software / configurations for CVE-2021-34705

Vendor Product Version Raw CPE
cisco ios 12.3\(7\)xm cpe:2.3:o:cisco:ios:12.3\(7\)xm:*:*:*:*:*:*:*
cisco ios 12.3\(7\)xr cpe:2.3:o:cisco:ios:12.3\(7\)xr:*:*:*:*:*:*:*
cisco ios 12.3\(7\)xr1 cpe:2.3:o:cisco:ios:12.3\(7\)xr1:*:*:*:*:*:*:*
cisco ios 12.3\(7\)xr2 cpe:2.3:o:cisco:ios:12.3\(7\)xr2:*:*:*:*:*:*:*
cisco ios 12.3\(7\)xr3 cpe:2.3:o:cisco:ios:12.3\(7\)xr3:*:*:*:*:*:*:*
cisco ios 12.3\(7\)xr4 cpe:2.3:o:cisco:ios:12.3\(7\)xr4:*:*:*:*:*:*:*
cisco ios 12.3\(7\)xr5 cpe:2.3:o:cisco:ios:12.3\(7\)xr5:*:*:*:*:*:*:*
cisco ios 12.3\(7\)xr6 cpe:2.3:o:cisco:ios:12.3\(7\)xr6:*:*:*:*:*:*:*
cisco ios 12.3\(7\)xr7 cpe:2.3:o:cisco:ios:12.3\(7\)xr7:*:*:*:*:*:*:*
cisco ios 12.3\(8\)ja2 cpe:2.3:o:cisco:ios:12.3\(8\)ja2:*:*:*:*:*:*:*
cisco ios 12.3\(8\)jea1 cpe:2.3:o:cisco:ios:12.3\(8\)jea1:*:*:*:*:*:*:*
cisco ios 12.3\(8\)jea2 cpe:2.3:o:cisco:ios:12.3\(8\)jea2:*:*:*:*:*:*:*
cisco ios 12.3\(8\)jea3 cpe:2.3:o:cisco:ios:12.3\(8\)jea3:*:*:*:*:*:*:*
cisco ios 12.3\(8\)jeb cpe:2.3:o:cisco:ios:12.3\(8\)jeb:*:*:*:*:*:*:*
cisco ios 12.3\(8\)jeb1 cpe:2.3:o:cisco:ios:12.3\(8\)jeb1:*:*:*:*:*:*:*
cisco ios 12.3\(8\)jec3 cpe:2.3:o:cisco:ios:12.3\(8\)jec3:*:*:*:*:*:*:*
cisco ios 12.3\(8\)jed1 cpe:2.3:o:cisco:ios:12.3\(8\)jed1:*:*:*:*:*:*:*
cisco ios 12.3\(8\)jee cpe:2.3:o:cisco:ios:12.3\(8\)jee:*:*:*:*:*:*:*
cisco ios 12.3\(8\)jk cpe:2.3:o:cisco:ios:12.3\(8\)jk:*:*:*:*:*:*:*
cisco ios 12.3\(8\)jk1 cpe:2.3:o:cisco:ios:12.3\(8\)jk1:*:*:*:*:*:*:*
cisco ios 12.3\(8\)t cpe:2.3:o:cisco:ios:12.3\(8\)t:*:*:*:*:*:*:*
cisco ios 12.3\(8\)t0a cpe:2.3:o:cisco:ios:12.3\(8\)t0a:*:*:*:*:*:*:*
cisco ios 12.3\(8\)t1 cpe:2.3:o:cisco:ios:12.3\(8\)t1:*:*:*:*:*:*:*
cisco ios 12.3\(8\)t2 cpe:2.3:o:cisco:ios:12.3\(8\)t2:*:*:*:*:*:*:*
cisco ios 12.3\(8\)t3 cpe:2.3:o:cisco:ios:12.3\(8\)t3:*:*:*:*:*:*:*
cisco ios 12.3\(8\)t4 cpe:2.3:o:cisco:ios:12.3\(8\)t4:*:*:*:*:*:*:*
cisco ios 12.3\(8\)t5 cpe:2.3:o:cisco:ios:12.3\(8\)t5:*:*:*:*:*:*:*
cisco ios 12.3\(8\)t6 cpe:2.3:o:cisco:ios:12.3\(8\)t6:*:*:*:*:*:*:*
cisco ios 12.3\(8\)t7 cpe:2.3:o:cisco:ios:12.3\(8\)t7:*:*:*:*:*:*:*
cisco ios 12.3\(8\)t8 cpe:2.3:o:cisco:ios:12.3\(8\)t8:*:*:*:*:*:*:*
cisco ios 12.3\(8\)t9 cpe:2.3:o:cisco:ios:12.3\(8\)t9:*:*:*:*:*:*:*
cisco ios 12.3\(8\)t10 cpe:2.3:o:cisco:ios:12.3\(8\)t10:*:*:*:*:*:*:*
cisco ios 12.3\(8\)t11 cpe:2.3:o:cisco:ios:12.3\(8\)t11:*:*:*:*:*:*:*
cisco ios 12.3\(8\)xu cpe:2.3:o:cisco:ios:12.3\(8\)xu:*:*:*:*:*:*:*
cisco ios 12.3\(8\)xu1 cpe:2.3:o:cisco:ios:12.3\(8\)xu1:*:*:*:*:*:*:*
cisco ios 12.3\(8\)xu2 cpe:2.3:o:cisco:ios:12.3\(8\)xu2:*:*:*:*:*:*:*
cisco ios 12.3\(8\)xu3 cpe:2.3:o:cisco:ios:12.3\(8\)xu3:*:*:*:*:*:*:*
cisco ios 12.3\(8\)xu4 cpe:2.3:o:cisco:ios:12.3\(8\)xu4:*:*:*:*:*:*:*
cisco ios 12.3\(8\)xu5 cpe:2.3:o:cisco:ios:12.3\(8\)xu5:*:*:*:*:*:*:*
cisco ios 12.3\(8\)xw cpe:2.3:o:cisco:ios:12.3\(8\)xw:*:*:*:*:*:*:*
cisco ios 12.3\(8\)xw1 cpe:2.3:o:cisco:ios:12.3\(8\)xw1:*:*:*:*:*:*:*
cisco ios 12.3\(8\)xw1a cpe:2.3:o:cisco:ios:12.3\(8\)xw1a:*:*:*:*:*:*:*
cisco ios 12.3\(8\)xw1b cpe:2.3:o:cisco:ios:12.3\(8\)xw1b:*:*:*:*:*:*:*
cisco ios 12.3\(8\)xw2 cpe:2.3:o:cisco:ios:12.3\(8\)xw2:*:*:*:*:*:*:*
cisco ios 12.3\(8\)xw3 cpe:2.3:o:cisco:ios:12.3\(8\)xw3:*:*:*:*:*:*:*
cisco ios 12.3\(8\)xx cpe:2.3:o:cisco:ios:12.3\(8\)xx:*:*:*:*:*:*:*
cisco ios 12.3\(8\)xx1 cpe:2.3:o:cisco:ios:12.3\(8\)xx1:*:*:*:*:*:*:*
cisco ios 12.3\(8\)xx2 cpe:2.3:o:cisco:ios:12.3\(8\)xx2:*:*:*:*:*:*:*
cisco ios 12.3\(8\)xx2a cpe:2.3:o:cisco:ios:12.3\(8\)xx2a:*:*:*:*:*:*:*
cisco ios 12.3\(8\)xx2b cpe:2.3:o:cisco:ios:12.3\(8\)xx2b:*:*:*:*:*:*:*
cisco ios 12.3\(8\)xx2c cpe:2.3:o:cisco:ios:12.3\(8\)xx2c:*:*:*:*:*:*:*
cisco ios 12.3\(8\)xx2d cpe:2.3:o:cisco:ios:12.3\(8\)xx2d:*:*:*:*:*:*:*
cisco ios 12.3\(8\)xx2e cpe:2.3:o:cisco:ios:12.3\(8\)xx2e:*:*:*:*:*:*:*
cisco ios 12.3\(8\)xy cpe:2.3:o:cisco:ios:12.3\(8\)xy:*:*:*:*:*:*:*
cisco ios 12.3\(8\)xy1 cpe:2.3:o:cisco:ios:12.3\(8\)xy1:*:*:*:*:*:*:*
cisco ios 12.3\(8\)xy2 cpe:2.3:o:cisco:ios:12.3\(8\)xy2:*:*:*:*:*:*:*
cisco ios 12.3\(8\)xy3 cpe:2.3:o:cisco:ios:12.3\(8\)xy3:*:*:*:*:*:*:*
cisco ios 12.3\(8\)xy4 cpe:2.3:o:cisco:ios:12.3\(8\)xy4:*:*:*:*:*:*:*
cisco ios 12.3\(8\)xy5 cpe:2.3:o:cisco:ios:12.3\(8\)xy5:*:*:*:*:*:*:*
cisco ios 12.3\(8\)xy6 cpe:2.3:o:cisco:ios:12.3\(8\)xy6:*:*:*:*:*:*:*
cisco ios 12.3\(8\)xy7 cpe:2.3:o:cisco:ios:12.3\(8\)xy7:*:*:*:*:*:*:*
cisco ios 12.3\(8\)yc cpe:2.3:o:cisco:ios:12.3\(8\)yc:*:*:*:*:*:*:*
cisco ios 12.3\(8\)yc1 cpe:2.3:o:cisco:ios:12.3\(8\)yc1:*:*:*:*:*:*:*
cisco ios 12.3\(8\)yc2 cpe:2.3:o:cisco:ios:12.3\(8\)yc2:*:*:*:*:*:*:*
cisco ios 12.3\(8\)yc3 cpe:2.3:o:cisco:ios:12.3\(8\)yc3:*:*:*:*:*:*:*
cisco ios 12.3\(8\)yd cpe:2.3:o:cisco:ios:12.3\(8\)yd:*:*:*:*:*:*:*
cisco ios 12.3\(8\)yd1 cpe:2.3:o:cisco:ios:12.3\(8\)yd1:*:*:*:*:*:*:*
cisco ios 12.3\(8\)yg cpe:2.3:o:cisco:ios:12.3\(8\)yg:*:*:*:*:*:*:*
cisco ios 12.3\(8\)yg1 cpe:2.3:o:cisco:ios:12.3\(8\)yg1:*:*:*:*:*:*:*
cisco ios 12.3\(8\)yg2 cpe:2.3:o:cisco:ios:12.3\(8\)yg2:*:*:*:*:*:*:*
cisco ios 12.3\(8\)yg3 cpe:2.3:o:cisco:ios:12.3\(8\)yg3:*:*:*:*:*:*:*
cisco ios 12.3\(8\)yg4 cpe:2.3:o:cisco:ios:12.3\(8\)yg4:*:*:*:*:*:*:*
cisco ios 12.3\(8\)yg5 cpe:2.3:o:cisco:ios:12.3\(8\)yg5:*:*:*:*:*:*:*
cisco ios 12.3\(8\)yg6 cpe:2.3:o:cisco:ios:12.3\(8\)yg6:*:*:*:*:*:*:*
cisco ios 12.3\(8\)yg7 cpe:2.3:o:cisco:ios:12.3\(8\)yg7:*:*:*:*:*:*:*
cisco ios 12.3\(8\)yi cpe:2.3:o:cisco:ios:12.3\(8\)yi:*:*:*:*:*:*:*
cisco ios 12.3\(8\)yi1 cpe:2.3:o:cisco:ios:12.3\(8\)yi1:*:*:*:*:*:*:*
cisco ios 12.3\(8\)yi2 cpe:2.3:o:cisco:ios:12.3\(8\)yi2:*:*:*:*:*:*:*
cisco ios 12.3\(8\)yi3 cpe:2.3:o:cisco:ios:12.3\(8\)yi3:*:*:*:*:*:*:*
cisco ios 12.3\(8\)za cpe:2.3:o:cisco:ios:12.3\(8\)za:*:*:*:*:*:*:*

References for CVE-2021-34705

cvelogic Threat Intelligence