CVE-2019-8514 : Detail

CVE-2019-8514

7.8
/
High
0.62%V3
Local
2019-12-18
16h33 +00:00
2019-12-18
16h33 +00:00
CVE.org
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CVE Descriptions

A logic issue was addressed with improved state management. This issue is fixed in iOS 12.2, macOS Mojave 10.14.4, tvOS 12.2, watchOS 5.2. An application may be able to gain elevated privileges.

CVE Informations

Related Weaknesses

CWE-ID Weakness Name Source
CWE Other No informations.

Metrics

Metrics Score Severity CVSS Vector Source
V3.1 7.8 HIGH CVSS:3.1/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

The vulnerable component is not bound to the network stack and the attacker’s path is via read/write/execute capabilities.

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 when attacking 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 of the vulnerable system to carry out an attack.

User Interaction

This metric captures the requirement for a human 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

The Scope metric captures whether a vulnerability in one vulnerable component impacts resources in components beyond its security scope.

Scope

Formally, a security authority is a mechanism (e.g., an application, an operating system, firmware, a sandbox environment) that defines and enforces access control in terms of how certain subjects/actors (e.g., human users, processes) can access certain restricted objects/resources (e.g., files, CPU, memory) in a controlled manner. All the subjects and objects under the jurisdiction of a single security authority are considered to be under one security scope. If a vulnerability in a vulnerable component can affect a component which is in a different security scope than the vulnerable component, a Scope change occurs. Intuitively, whenever the impact of a vulnerability breaches a security/trust boundary and impacts components outside the security scope in which vulnerable component resides, a Scope change occurs.

Unchanged

An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.

Base: Impact Metrics

The Impact metrics capture the effects of a successfully exploited vulnerability on the component that suffers the worst outcome that is most directly and predictably associated with the attack. Analysts should constrain impacts to a reasonable, final outcome which they are confident an attacker is able to achieve.

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 a 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 a 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 in the description of a vulnerability.

Environmental Metrics

These metrics enable the analyst to customize the CVSS score depending on the importance of the affected IT asset to a user’s organization, measured in terms of Confidentiality, Integrity, and Availability.

 [email protected]
V2 6.8 AV:N/AC:M/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 : 46648

Publication date : 2019-04-02 22h00 +00:00
Author : Google Security Research
EDB Verified : Yes

Privileged IPC services in userspace often have to verify the security context of their client processes (such as whether the client is sandboxed, has a specific entitlement, or is signed by some code signing authority). This, in turn, requires a way to identify a client process. If PIDs are used for that purpose, the following attack becomes possible: 1. The (unprivileged) client process sends an IPC message to a privileged service 2. The client process terminates and spawns a privileged process into its PID 3. The privileged service performs the security check, but since the PID has been reused it performs it on the wrong process This attack is feasible because the PID space is usually fairly small (e.g. 100000 for XNU) and PIDs can thus be wrapped around relatively quickly (in step 2 or up front). As such, on darwin platforms the recommended way to identify IPC clients for the purpose of performing security checks in userspace is to rely on the audit_token. In contrast to the PID, which wraps around at 100000, the audit_token additionally contains the pidversion, which is in essence a 32-bit PID (from bsd/kern/kern_fork.c): proc_t forkproc(proc_t parent_proc) { static int nextpid = 0, pidwrap = 0, nextpidversion = 0; ...; /* Repeat until nextpid is a currently unused PID. */ nextpid++; ...; nprocs++; child_proc->p_pid = nextpid; child_proc->p_responsible_pid = nextpid; child_proc->p_idversion = nextpidversion++; ...; When using audit_tokens, the previously described attack would now require creating two different processes which have the same pair of (pid, pidversion), which in turn would require spawning roughly 2**32 processes to wrap around the pidversion. However, the pidversion is additionally incremented during execve (from bsd/kern/kern_exec.c): /* Update the process' identity version and set the security token */ p->p_idversion++; This is likely done to prevent another attack where a process sends an IPC message, then immediately execve's a privileged binary. The problem here is that the pidversion is incremented "ad-hoc", without updating the global nextpidversion variable. With that it becomes possible to create two processes with the same (pid, pidversion) pair without wrapping around the 32-bit pidversion: 1. The initial exploit process is identified by the pair (pid: X, pidversion: Y) 2. The exploit performs 10000 execves to get (X, Y + 100000) 3. The exploit interacts with a privileged service which stores the client's audit_token (or directly uses it, in which case the following part becomes a race) 4. The exploit forks, with the parent processes immediately terminating, until it has the same PID again. This could, for example, require 99000 forks (because some PIDs are in use). The process now has (X, Y + 99000) 5. The exploit execves until it has (X, Y + 99999) 6. The exploit execves a privileged binary. The privileged binary will have (X, Y + 100000) 7. At this time the privileged service performs a security check of the client but will perform this check on the entitled process even though the request came from an unprivileged process The attached PoC demonstrates this by showing that an IPC service can be tricked into believing that the client has a specific entitlement. To reproduce: 1. compile the attached code: `make` 2. start the helper service: `./service`. The service simply prints the value of a predefined entitlement (currently "com.apple.private.AuthorizationServices") of a connected client 3. in a separate shell start the exploit: `./exploit`. 4. once the exploit prints "[+] All done. Spawning sudo now", press enter in the shell where the helper service is running. It should now print the value of the entitlement. The gained primitive (obtaining more or less arbitrary entitlements) can then e.g. be used as described here: https://gist.github.com/ChiChou/e3a50f00853b2fbfb1debad46e501121. Besides entitlements, it should also be possible to spoof code signatures this way. Furthermore, it might be possible to use this bug for a sandbox escape if one is able to somehow perform execve (there are multiple sandboxed services and applications that have (allow process-exec) in their sandbox profile for example). In that case, one could spawn a non-sandboxed system service into the same (pid, pidversion) pair prior to performing some IPC operations where the endpoint will do a sandbox_check_by_audit_token. However, precisely spawning a non-sandboxed process into the same (pid, pidversion) will likely be a lot less reliable. Proof of Concept: https://gitlab.com/exploit-database/exploitdb-bin-sploits/-/raw/main/bin-sploits/46648.zip

Products Mentioned

Configuraton 0

Apple>>Iphone_os >> Version To (excluding) 12.2

Apple>>Mac_os_x >> Version To (excluding) 10.14.4

Apple>>Tvos >> Version To (excluding) 12.2

Apple>>Watchos >> Version To (excluding) 5.2

References