CVE-2019-8646 : Detail

CVE-2019-8646

7.5
/
High
Overflow
12.76%V3
Network
2019-12-18
16h33 +00:00
2019-12-18
16h33 +00:00
CVE.org
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CVE Descriptions

An out-of-bounds read was addressed with improved input validation. This issue is fixed in iOS 12.4, macOS Mojave 10.14.6, tvOS 12.4, watchOS 5.3. A remote attacker may be able to leak memory.

CVE Informations

Related Weaknesses

CWE-ID Weakness Name Source
CWE-125 Out-of-bounds Read
The product reads data past the end, or before the beginning, of the intended buffer.

Metrics

Metrics Score Severity CVSS Vector Source
V3.1 7.5 HIGH CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

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.

Network

The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed below, up to and including the entire Internet. Such a vulnerability is often termed “remotely exploitable” and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).

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.

None

The vulnerable system can be exploited without interaction from any user.

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.

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 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 5 AV:N/AC:L/Au:N/C:P/I:N/A:N [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 : 47194

Publication date : 2019-07-29 22h00 +00:00
Author : Google Security Research
EDB Verified : Yes

The class _NSDataFileBackedFuture can be deserialized even if secure encoding is enabled. This class is a file-backed NSData object that loads a local file into memory when the [NSData bytes] selector is called. This presents two problems. First, it could potentially allow undesired access to local files if the code deserializing the buffer ever shares it (this is more likely to cause problems in components that use serialized objects to communicate locally than in iMessage). Second, it allows an NSData object to be created with a length that is different than the length of its byte array. This violates a very basic property that should always be true of NSData objects. This can allow out of bounds reads, and could also potentially lead to out-of-bounds writes, as it is now possible to create NSData objects with very large sizes that would not be possible if the buffer was backed. To reproduce the issue with the files in filebacked.zip: 1) install frida (pip3 install frida) 2) open sendMessage.py, and replace the sample receiver with the phone number or email of the target device 3) in injectMessage.js replace the marker "PATH" with the path of the obj file 4) in the local directory, run: python3 sendMessage.py Please note that the attached repro case is a simple example to demonstrate the reach-ability of the class in Springboard. The actual consequences of the bug are likely more serious. This PoC only works on devices with iOS 12 or later. I've written up a PoC of this issue leaking memory from a remote device. To use the PoC, replace all instances of "natashenka.party" in the attached files with the domain of the server you are using to reproduce the issue. Then run myserver.py on the server, and use the files in filebackedleak.zip to send a message to a target device, using the instructions in the issue above. Leaked bytes of memory from Springboard in the target device will be displayed in the output of myserver.py. A quick summary of how this PoC works: 1) iMessage attempts to decode the object in the file obj to display the message notification 2) A _NSDataFileBackedFuture instance is decoded, with a fileURL of http://natashenka.party//System/Library/ColorSync/Resources/ColorTables.data and a long length. 3) An ACZeroingString instance is decoded, using the previous _NSDataFileBackedFuture as its bytes. When the bytes are accessed, they will be fetched from the above URL. The _NSDataFileBackedFuture class attempts to prevent remote URLs from being fetched by checking that the path of the URL exists on the system, but it does not check the scheme, so a remote URL can be fetched so long as its path component is a path that exists on the filesystem 4) The remote server responds with a buffer that contains the URL http://natashenka.party//System/Library/ColorSync/Resources/ColorTables.data?val=a. Since the length of the _NSDataFileBackedFuture is long, this will lead to a buffer that contains the URL as well as some unallocated, uninitialized memory 5) Unfortunately, it is not possible to leak the memory by accessing the URL with the leaked memory created in step 4 using another _NSDataFileBackedFuture at this stage, because the NSURL class greatly restricts the characters allowed in a URL, so it is necessary to bypass these checks. It is possible to do this with the INDeferredLocalizedString class, which is a string that can have different values based on localization 6) An INDeferredLocalizedString instance is decoded with one property being a string that is a legal URL, and the other being the string with the invalid characters. There is a cycle in initialization that causes an NSURL instance to be initialized using the valid string, but then the string moves into a state where it will return the invalid characters when the NSURL is used. 7) A _NSDataFileBackedFuture is used to access the URL, and the leaked bytes are send to the server as the URL parameter I've got this issue to read files from a remote device. To use the PoC, replace all instances of "natashenka.party" in the attached files with the domain of the server you are using to reproduce the issue. Then run myserver.py on the server, and use the files in messageleak.zip to send a message to a target device, using the instructions in the issue above. There are two possible objects to send the device: obj_db: sends back the file in an escaped format that omits nulls. Good for leaking the SMS database obj_image: sends back the file in a url encoded format. Good for leaking binary files like images The file contents will be output on the commandline of myserver.py. There are some length limits in the server file that can be removed to see more data. The server will also output a file named 'buf'. Processing this file with uni.py (requires python3) will output the file. This only works with the the obj_image object. This PoC works similarly to the one above, but it encodes the string by using the formatting options in INDeferredLocalizedString. Proof of Concept: https://gitlab.com/exploit-database/exploitdb-bin-sploits/-/raw/main/bin-sploits/47194.zip

Products Mentioned

Configuraton 0

Apple>>Iphone_os >> Version To (excluding) 12.4

Apple>>Mac_os_x >> Version To (excluding) 10.14.6

Apple>>Tvos >> Version To (excluding) 12.4

Apple>>Watchos >> Version To (excluding) 5.3

References