블로그 구독

Red Hat Product Security was made aware of a vulnerability affecting the Linux kernel's implementation of the Bluetooth L2CAP protocol.  The vulnerability was named BlueBorne and was assigned an ID - CVE-2017-1000251.

A vulnerable system would need to have Bluetooth (hardware + service) enabled and an attacking device would need to be within 

its operating range.

Bluetooth is a short-range wireless communication technology meant to connect devices over radio channels without need for a physical connection. The radio channel forms a physical layer in the Bluetooth stack, analogous to cables in other networks. Above this physical channel, the Bluetooth stack hosts different logical channels and their associated protocols, such as Link Manager Protocol (LMP), Logical Link Control and Adaptation Protocol (L2CAP) and others. These protocols help with controlling the operation of devices in the Bluetooth network and provide services such as segmentation/reassembly of application data, error detection, retransmission and multiplexing of channels over a shared link.

A typical Bluetooth operation includes device discovery, connection establishment and configuration followed by data transmission. A radio channel provides a physical link between two devices. The L2CAP (Logical link control and adaptation protocol) channel provides a logical connection between two devices which could serve a single application. Multiple such logical connections share a physical link between two devices.

Kernel buffer overflow

Once a physical connection is established, L2CAP configures a logical link between two end-points to be used by an application. It is during this configuration of a channel that the stack buffer overflow issue can occur. L2CAP implementation in the Linux kernel stores these configuration parameters in a stack buffer object:

case L2CAP_CONF_PENDING:
    ....
    if (test_bit(CONF_LOC_CONF_PEND, &chan->conf_state)) {
        char buf[64];  <= Kernel stack buffer stores L2CAP parameters

        len = l2cap_parse_conf_rsp(chan, rsp->data, len, buf, &result);
A Bluetooth client sends configuration parameters to a host, these are temporarily stored in the “buf” array above.

A malicious client can send L2CAP configuration packets with configuration parameters set to exceed 64 byte length of the “buf” array passed to the l2cap_parse_conf_rsp() routine. When these parameters are copied to the "buf" array, adjacent kernel stack memory is overwritten with their content. This exchange occurs prior to any authentication, while establishing a Bluetooth connection. As a result, an unauthenticated user who is able to connect to a system via Bluetooth, can use this flaw to overwrite kernel stack memory with malicious data.

System guards

Kernel stack memory corruption can be easily leveraged to execute arbitrary code with kernel ring 0 (above root) privileges on a system. Red Hat Enterprise Linux kernels are hardened with gcc(1) compile time options which protect against such memory corruption. On supported architectures the gcc(1) -fstack-protector option adds a canary value at the beginning of a function and before the function return address. The -fstack-protector-strong extends this canary protection around local stack variables including arrays of any type and length. As can be seen below,

BlueBorne - CVE-2017-1000251

After copying data to these stack variables, kernel validates the stack canary value stored in the stack frame to detect any memory corruption and aborts the impending attack by resorting to a kernel panic.

void __stack_chk_fail(void)
{
    panic("stack-protector: Kernel stack is corrupted in: %p\n",
            __builtin_return_address(0));
}

The stack protection thus helps to prevent the arbitrary code execution with the kernel/root privileges.  Ie. on cpu architectures with support for this feature, this vulnerability is reduced to a denial of service, rather than a remote code execution one.

Response

Red Hat Enterprise Linux kernels have received updates to address this buffer overflow.  The kernel functions 'L2cap_parse_conf_rsp' and 'l2cap_add_conf_opt' have been augmented to accept a new parameter specifying the length of the "buf" array. These functions then use the length parameter to contain the data copied from an incoming packet within "buf" limits, so as to prevent the stack buffer overflow.

 

Acknowledgements:

Red Hat would like to thank Armis Labs (https://armis.com) for reporting this issue.


[*] https://access.redhat.com/security/vulnerabilities/blueborne


저자 소개

채널별 검색

automation icon

오토메이션

기술, 팀, 인프라를 위한 IT 자동화 최신 동향

AI icon

인공지능

고객이 어디서나 AI 워크로드를 실행할 수 있도록 지원하는 플랫폼 업데이트

open hybrid cloud icon

오픈 하이브리드 클라우드

하이브리드 클라우드로 더욱 유연한 미래를 구축하는 방법을 알아보세요

security icon

보안

환경과 기술 전반에 걸쳐 리스크를 감소하는 방법에 대한 최신 정보

edge icon

엣지 컴퓨팅

엣지에서의 운영을 단순화하는 플랫폼 업데이트

Infrastructure icon

인프라

세계적으로 인정받은 기업용 Linux 플랫폼에 대한 최신 정보

application development icon

애플리케이션

복잡한 애플리케이션에 대한 솔루션 더 보기

Original series icon

오리지널 쇼

엔터프라이즈 기술 분야의 제작자와 리더가 전하는 흥미로운 스토리