The vulnerable system is bound to the network stack and the set of possible attackers extends beyond the other options listed below, up to and including the entire Internet. Such a vulnerability is often termed “remotely exploitable” and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers). An example of a network attack is an attacker causing a denial of service by sending a specially crafted TCP packet across a wide area network (e.g., CVE-2004-0230).
Attack Complexity
Low
AC
The attacker must take no measurable action to exploit the vulnerability. The attack requires no target-specific circumvention to exploit the vulnerability. An attacker can expect repeatable success against the vulnerable system.
Privileges Required
None
PR
The attacker is unauthenticated prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.
Scope
Unchanged
S
An exploited vulnerability can only affect resources managed by the same security authority. In the case of a vulnerability in a virtualized environment, an exploited vulnerability in one guest instance would not affect neighboring guest instances.
Confidentiality
High
C
There is total information disclosure, resulting in all data on the system being revealed to the attacker, or there is a possibility of the attacker gaining control over confidential data.
Integrity
High
I
There is a total compromise of system integrity. There is a complete loss of system protection, resulting in the attacker being able to modify any file on the target system.
Availability
High
A
There is a total shutdown of the affected resource. The attacker can deny access to the system or data, potentially causing significant loss to the organization.
Broadcom Wi-Fi SoC dhd_handle_swc_evt Heap OverflowBroadcom produces Wi-Fi HardMAC SoCs which are used to handle the PHY and MAC layer processing. These chips are present in both mobile devices and Wi-Fi routers, and are capable of handling many Wi-Fi related events without delegating to the host OS. On Android devices, the "bcmdhd" driver is used in order to communicate with the Wi-Fi SoC (also referred to as "dongle").
When the dongle wishes to notify the host OS of an event, it does so by encoding a special "packet" and transmitting it to the host. These packets have an ether type of 0x886C (referred to as ETHER_TYPE_BRCM), and do not contain actual packet data, but rather encapsulate information about events which must be handled by the driver.
After reading packets from the SDIO interface, the "bcmdhd" driver calls the function "dhd_rx_frame" to handle each of the received frames. If a frame has the special Broadcom ether type, it is passed on to an internal handling function, "dhd_wl_host_event". This function inspects the event code, and passes it onto the registered handlers for the given event type.
The function "wl_notify_gscan_event" is the registered handler for events of the following types:
-WLC_E_PFN_BEST_BATCHING
-WLC_E_PFN_SCAN_COMPLETE
-WLC_E_PFN_GSCAN_FULL_RESULT
-WLC_E_PFN_SWC
-WLC_E_PFN_BSSID_NET_FOUND
-WLC_E_PFN_BSSID_NET_LOST
-WLC_E_PFN_SSID_EXT
-WLC_E_GAS_FRAGMENT_RX
(for reference, see "wl_init_event_handler")
Specifically, when the event code "WLC_E_PFN_SWC" is received, the gscan handler function calls "dhd_handle_swc_evt" in order to process the event's data, like so:
1. void * dhd_handle_swc_evt(dhd_pub_t *dhd, const void *event_data, int *send_evt_bytes)
2. {
3. ...
4. wl_pfn_swc_results_t *results = (wl_pfn_swc_results_t *)event_data;
5. ...
6. gscan_params = &(_pno_state->pno_params_arr[INDEX_OF_GSCAN_PARAMS].params_gscan);
7. ...
8. if (!params->results_rxed_so_far) {
9. if (!params->change_array) {
10. params->change_array = (wl_pfn_significant_net_t *)
11. kmalloc(sizeof(wl_pfn_significant_net_t) * results->total_count, GFP_KERNEL);
12. ...
13. }
14. }
15. ...
16. change_array = ¶ms->change_array[params->results_rxed_so_far];
17. memcpy(change_array, results->list, sizeof(wl_pfn_significant_net_t) * results->pkt_count);
18. params->results_rxed_so_far += results->pkt_count;
19. ...
20. }
(where "event_data" is the arbitrary data encapsulated in the event passed in from the dongle)
When the function above is first invoked, the value of "params->change_array" is NULL. An attacker controlling the dongle may send a crafted WLC_E_PFN_SWC event, with the following values:
- results->total_count = SMALL_VALUE
- result->pkt_count = LARGE_VALUE
Since the function fails to verify that "pkt_count" is not larger than "total_count", this would cause the allocated buffer (lines 10-11) to be smaller than the size used in the memcpy operation (line 17), thus overflowing the buffer.
I've been able to statically verify these issues on the "bcmdhd-3.10" driver, and in the corresponding "bcmdhd" driver on the Nexus 6P's kernel (angler).
Adding sample EtherType exploit which achieves kernel code execution on the Nexus 5.
This exploit uses scapy-fakeap to broadcast a dummy network. The exploit starts the attack once a client with the target MAC connects to the network and sends an ARP request.
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