CVE-2017-12240
CriticalExploitedPublic exploitThe DHCP relay subsystem of Cisco IOS 12.2 through 15.6 and Cisco IOS XE Software contains a vulnerability that could allow an unauthenticated, remote attacker to execute arbitrary code and gain full control of an affected system.
Published Sep 28, 2017 · Updated Apr 21, 2026
Key Facts
Patch immediately- CVE-2017-12240 is a critical-severity vulnerability (CVSS 9.8 v3.1) affecting IOS (Cisco), Cisco IOS and IOS XE.
- It is exploited in the wild, listed in CISA KEV, Industry KEV feed, CIRCL KEV, ENISA EUVD since Mar 3, 2022. Public exploit code is available.
- EPSS estimates a 14% probability of exploitation in the next 30 days.
- Fixed versions are available, including IOS 15.6.
- Brandefense priority: patch immediately, because it is listed as exploited in the wild.
CVSS v3.1
9.8
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
EPSS (30-day exploit likelihood)
14%
Higher than 96.4% of all scored CVEs
Exploited in the wild
Yes
4 catalog listings
Public exploit code
Available
Proof-of-concept or weaponized module
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Description
The DHCP relay subsystem of Cisco IOS 12.2 through 15.6 and Cisco IOS XE Software contains a vulnerability that could allow an unauthenticated, remote attacker to execute arbitrary code and gain full control of an affected system. The attacker could also cause an affected system to reload, resulting in a denial of service (DoS) condition. The vulnerability is due to a buffer overflow condition in the DHCP relay subsystem of the affected software. An attacker could exploit this vulnerability by sending a crafted DHCP Version 4 (DHCPv4) packet to an affected system. A successful exploit could allow the attacker to execute arbitrary code and gain full control of the affected system or cause the affected system to reload, resulting in a DoS condition. Cisco Bug IDs: CSCsm45390, CSCuw77959.
Known-Exploited Catalog Listings
| Catalog | Added | Remediation due | Ransomware use |
|---|---|---|---|
| CISA KEV | Mar 3, 2022 | Mar 24, 2022 | Not reported |
| Industry KEV feed | Mar 3, 2022 | Mar 24, 2022 | Not reported |
| CIRCL KEV | Mar 3, 2022 | Mar 24, 2022 | Not reported |
| ENISA EUVD | Mar 3, 2022 | n/a | Not reported |
Required action: Apply updates per vendor instructions.
Affected Products
2 affected entries in total| Product | Affected versions | Fixed in |
|---|---|---|
| IOSCisco | See advisory | 15.6 |
| Cisco IOS and IOS XE | >= Cisco IOS and IOS XE | n/a |
Patched Releases
IOS
15.6
Timeline
Publicly disclosed
Sep 28, 2017
Added to CISA KEV
Mar 3, 2022
Added to Industry KEV feed
Mar 3, 2022
Added to CIRCL KEV
Mar 3, 2022
Added to ENISA EUVD
Mar 3, 2022
Last updated
Apr 21, 2026
Weakness Type
- CWE-20 Improper Input Validation
- CWE-119 Improper Restriction of Operations within the Bounds of a Memory Buffer
References
- advisoryhttps://quickview.cloudapps.cisco.com/quickview/bug/CSCsm45390
- advisoryhttps://quickview.cloudapps.cisco.com/quickview/bug/CSCuw77959
- advisoryhttps://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20170927-dhcp
- advisory101034
- advisory1039445
FAQ
Common Questions.
The DHCP relay subsystem of Cisco IOS 12.2 through 15.6 and Cisco IOS XE Software contains a vulnerability that could allow an unauthenticated, remote attacker to execute arbitrary code and gain full control of an affected system.
Affected: IOS (Cisco); Cisco IOS and IOS XE versions >= Cisco IOS and IOS XE. The full list is in the CVE brief.
It is exploited in the wild, listed in CISA KEV, Industry KEV feed, CIRCL KEV, ENISA EUVD since Mar 3, 2022.
Yes. It was added on Mar 3, 2022 with a federal remediation due date of Mar 24, 2022.
Public exploit code is available.
Fixed versions are available, including IOS 15.6.
Brandefense priority: patch immediately, because it is listed as exploited in the wild.
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