A vulnerability in the DHCP code for the Zero Touch Provisioning feature of Cisco ASR 920 Series Aggregation Services Routers could allow an unauthenticated, remote attacker to cause an affected device to reload. The vulnerability is due to a format string vulnerability when processing a crafted DHCP packet for Zero Touch Provisioning. An attacker could exploit this vulnerability by sending a specially crafted DHCP packet to an affected device. An exploit could allow the attacker to cause the device to reload, resulting in a denial of service (DoS) condition. This vulnerability affects Cisco ASR 920 Series Aggregation Services Routers that are running an affected release of Cisco IOS XE Software (3.13 through 3.18) and are listening on the DHCP server port. By default, the devices do not listen on the DHCP server port. Cisco Bug IDs: CSCuy56385.
The product uses a function that accepts a format string as an argument, but the format string originates from an external source.
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Ios_xe | Cisco | 3.13.4s (including) | 3.13.4s (including) |
| Ios_xe | Cisco | 3.13.5as (including) | 3.13.5as (including) |
| Ios_xe | Cisco | 3.13.5s (including) | 3.13.5s (including) |
| Ios_xe | Cisco | 3.13.6as (including) | 3.13.6as (including) |
| Ios_xe | Cisco | 3.13.6s (including) | 3.13.6s (including) |
| Ios_xe | Cisco | 3.14.3s (including) | 3.14.3s (including) |
| Ios_xe | Cisco | 3.14.4s (including) | 3.14.4s (including) |
| Ios_xe | Cisco | 3.15.2s (including) | 3.15.2s (including) |
| Ios_xe | Cisco | 3.15.3s (including) | 3.15.3s (including) |
| Ios_xe | Cisco | 3.15.4s (including) | 3.15.4s (including) |
| Ios_xe | Cisco | 3.16.0cs (including) | 3.16.0cs (including) |
| Ios_xe | Cisco | 3.16.0s (including) | 3.16.0s (including) |
| Ios_xe | Cisco | 3.16.1as (including) | 3.16.1as (including) |
| Ios_xe | Cisco | 3.16.1s (including) | 3.16.1s (including) |
| Ios_xe | Cisco | 3.16.2as (including) | 3.16.2as (including) |
| Ios_xe | Cisco | 3.16.2bs (including) | 3.16.2bs (including) |
| Ios_xe | Cisco | 3.16.2s (including) | 3.16.2s (including) |
| Ios_xe | Cisco | 3.16.3as (including) | 3.16.3as (including) |
| Ios_xe | Cisco | 3.16.3s (including) | 3.16.3s (including) |
| Ios_xe | Cisco | 3.17.0s (including) | 3.17.0s (including) |
| Ios_xe | Cisco | 3.17.1as (including) | 3.17.1as (including) |
| Ios_xe | Cisco | 3.17.1s (including) | 3.17.1s (including) |
| Ios_xe | Cisco | 3.17.2s (including) | 3.17.2s (including) |
| Ios_xe | Cisco | 3.18.0as (including) | 3.18.0as (including) |
| Ios_xe | Cisco | 3.18.0s (including) | 3.18.0s (including) |
| Ios_xe | Cisco | 3.18.0sp (including) | 3.18.0sp (including) |
| Ios_xe | Cisco | 3.18.1asp (including) | 3.18.1asp (including) |
| Ios_xe | Cisco | 3.18.1bsp (including) | 3.18.1bsp (including) |
| Ios_xe | Cisco | 3.18.1csp (including) | 3.18.1csp (including) |
| Ios_xe | Cisco | 3.18.1s (including) | 3.18.1s (including) |
| Ios_xe | Cisco | 3.18.1sp (including) | 3.18.1sp (including) |
| Ios_xe | Cisco | 3.18.2s (including) | 3.18.2s (including) |
| Ios_xe | Cisco | 3.18.3vs (including) | 3.18.3vs (including) |
When an attacker can modify an externally-controlled format string, this can lead to buffer overflows, denial of service, or data representation problems. It should be noted that in some circumstances, such as internationalization, the set of format strings is externally controlled by design. If the source of these format strings is trusted (e.g. only contained in library files that are only modifiable by the system administrator), then the external control might not itself pose a vulnerability.