CVE-2019-8611

Score / Severity

8.8

High

CVE Descriptions

Multiple memory corruption issues were addressed with improved memory handling. This issue is fixed in iOS 12.3, macOS Mojave 10.14.5, tvOS 12.3, Safari 12.1.1, iTunes for Windows 12.9.5, iCloud for Windows 7.12. 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 More informations 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.	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.

Date	EPSS V0	EPSS V1	EPSS V2 (> 2022-02-04)	EPSS V3 (> 2025-03-07)	EPSS V4 (> 2025-03-17)
2021-04-18	1.66%	–	–	–	–
2021-09-05	–	1.66%	–	–	–
2021-11-07	–	1.66%	–	–	–
2022-01-09	–	1.66%	–	–	–
2022-02-06	–	–	49.16%	–	–
2022-04-03	–	–	15.95%	–	–
2023-03-12	–	–	–	91.91%	–
2023-07-23	–	–	–	91.91%	–
2023-08-20	–	–	–	91.52%	–
2023-08-27	–	–	–	91.52%	–
2023-09-10	–	–	–	91.64%	–
2023-10-08	–	–	–	91.73%	–
2023-10-22	–	–	–	92.54%	–
2023-11-26	–	–	–	92.66%	–
2024-06-02	–	–	–	92.66%	–
2024-07-14	–	–	–	90.25%	–
2024-08-04	–	–	–	90.71%	–
2024-08-25	–	–	–	88.97%	–
2024-09-08	–	–	–	90.08%	–
2024-12-15	–	–	–	91.12%	–
2024-12-22	–	–	–	69.54%	–
2024-12-29	–	–	–	65%	–
2025-02-09	–	–	–	58.72%	–
2025-01-19	–	–	–	65%	–
2025-02-16	–	–	–	58.72%	–
2025-03-18	–	–	–	–	28.04%
2025-03-18	–	–	–	–	28.04,%

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

Date	Percentile
2021-04-18	–
2021-09-05	74%
2021-11-07	75%
2022-01-09	34%
2022-02-06	98%
2022-04-03	96%
2023-03-12	98%
2023-07-23	99%
2023-08-20	98%
2023-08-27	99%
2023-09-10	99%
2023-10-08	99%
2023-10-22	99%
2023-11-26	99%
2024-06-02	99%
2024-07-14	99%
2024-08-04	99%
2024-08-25	99%
2024-09-08	99%
2024-12-15	99%
2024-12-22	98%
2024-12-29	98%
2025-02-09	98%
2025-01-19	98%
2025-02-16	98%
2025-03-18	96%
2025-03-18	96%

Exploit information

Exploit Database EDB-ID : 46890

Publication date : 2019-05-20 22h00 +00:00
Author : Google Security Research
EDB Verified : Yes

While fuzzing JavaScriptCore, I encountered the following JavaScript program which crashes jsc from current HEAD (git commit 3c46422e45fef2de6ff13b66cd45705d63859555) in debug and release builds (./Tools/Scripts/build-jsc --jsc-only [--debug or --release]): // Run with --useConcurrentJIT=false --thresholdForJITAfterWarmUp=10 --thresholdForFTLOptimizeAfterWarmUp=1000 function v0(v1) { function v7(v8) { function v12(v13, v14) { const v16 = v14 - -0x80000000; const v19 = [13.37, 13.37, 13.37]; function v20() { return v16; } return v19; } return v8(v12, v1); } const v27 = v7(v7); } for (let i = 0; i < 100; i++) { v0(i); } It appears that what is happening here is roughly the following: Initially, the call to v12 is inlined and the IR contains (besides others) the following instructions for the inlined v12: 1 <- GetScope() 2 <- CreateActivation(1) 3 <- GetLocal(v14) 4 <- JSConstant(-0x80000000) 5 <- ValueSub(3, 4) 6 <- NewArrayBuffer(...) Here, The CreateActivation instruction allocates a LexicalEnvironment object on the heap to store local variables into. The NewArrayBuffer allocates backing memory for the array. Next, the subtraction is (incorrectly?) speculated to not overflow and is thus replaced by an ArithSub, an instruction performing an integer subtraction and bailing out if an overflow occurs: 1 <- GetScope() 2 <- CreateActivation(1) 3 <- GetLocal(v14) 4 <- JSConstant(-0x80000000) 5 <- ArithSub(3, 4) 6 <- NewArrayBuffer(...) Next, the object allocation sinking phase runs, which determines that the created activation object doesn't leave the current scope and thus doesn't have to be allocated at all. It then replaces it with a PhancomCreateActivation, a node indicating that at this point a heap allocation used to happen which would have to be restored ("materialized") during a bailout because the interpreter/baseline JIT expects it to be there. As the scope object is required to materialize the Activation, a PutHint is created which indicates that during a bailout, the result of GetScope must be available somehow. 1 <- GetScope() 2 <- PhantomCreateActivation() 7 <- PutHint(2, 1) 3 <- GetLocal(v14) 4 <- JSConstant(-0x80000000) 5 <- ArithSub(3, 4) 6 <- NewArrayBuffer(...) The DFG IR code is then lowered to B3, yielding the following: Int64 @66 = Const64(16, DFG:@1) Int64 @67 = Add(@35, $16(@66), DFG:@1) Int64 @68 = Load(@67, ControlDependent|Reads:28, DFG:@1) Int32 @69 = Const32(-2147483648, DFG:@5) Int32 @70 = CheckSub(@48:WarmAny, $-2147483648(@69):WarmAny, @35:ColdAny, @48:ColdAny, @68:ColdAny, @41:ColdAny, ...) Int64 @74 = Patchpoint(..., DFG:@6) Here, the first three operations fetch the current scope, the next two instruction perform the checked integer subtraction, and the last instruction performs the array storage allocation. Note that the scope object (@68) is an operand for the subtraction as it is required for the materialization of the activation during a bailout. The B3 code is then (after more optimizations) lowered to AIR: Move %tmp2, (stack0), @65 Move 16(%tmp2), %tmp28, @68 Move $-2147483648, %tmp29, $-2147483648(@69) Move %tmp4, %tmp27, @70 Patch &BranchSub32(3,SameAsRep)4, Overflow, $-2147483648, %tmp27, %tmp2, %tmp4, %tmp28, %tmp5, @70 Patch &Patchpoint2, %tmp24, %tmp25, %tmp26, @74 Then, after optimizations on the AIR code and register allocation: Move %rax, (stack0), @65 Move 16(%rax), %rdx, @68 Patch &BranchSub32(3,SameAsRep)4, Overflow, $-2147483648, %rcx, %rax, %rcx, %rdx, %rsi, @70 Patch &Patchpoint2, %rax, %rcx, %rdx, @74 Finally, in the reportUsedRegisters phase (AirReportUsedRegisters.cpp), the following happens * The register rdx is marked as "lateUse" for the BranchSub32 and as "earlyDef" for the Patchpoint (this might ultimately be the cause of the issue). "early" and "late" refer to the time the operand is used/defined, either before the instruction executes or after. * As such, at the boundary (which is where register liveness is computed) between the last two instructions, rdx is both defined and used. * Then, when liveness is computed (in AirRegLiveness.cpp) for the boundary between the Move and the BranchSub32, rdx is determined to be dead as it is not used at the boundary and defined at the following boundary: // RegLiveness::LocalCalc::execute void execute(unsigned instIndex) { m_workset.exclude(m_actions[instIndex + 1].def); m_workset.merge(m_actions[instIndex].use); } As a result, the assignment to rdx (storing the pointer to the scope object), is determined to be a store to a dead register and is thus discarded, leaving the following code: Move %rax, (stack0), @65 Patch &BranchSub32(3,SameAsRep)4, Overflow, $-2147483648, %rcx, %rax, %rcx, %rdx, %rsi, @70 Patch &Patchpoint2, %rax, %rcx, %rdx, @74 As such, whatever used to be in rdx will then be treated as a pointer to a scope object during materialization of the activation in the case of a bailout, leading to a crash similar to the following: * thread #1, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1, address=0xbbadbeef) * frame #0: 0x0000000101a88b20 JavaScriptCore`::WTFCrash() at Assertions.cpp:255 frame #1: 0x00000001000058fb jsc`WTFCrashWithInfo((null)=521, (null)="../../Source/JavaScriptCore/runtime/JSCJSValueInlines.h", (null)="JSC::JSCell *JSC::JSValue::asCell() const", (null)=1229) at Assertions.h:560 frame #2: 0x000000010000bdbb jsc`JSC::JSValue::asCell(this=0x00007ffeefbfcf78) const at JSCJSValueInlines.h:521 frame #3: 0x0000000100fe5fbd JavaScriptCore`::operationMaterializeObjectInOSR(exec=0x00007ffeefbfd230, materialization=0x0000000106350f00, values=0x00000001088e7448) at FTLOperations.cpp:217 frame #4: ... (lldb) up 2 frame #2: 0x000000010000bdbb jsc`JSC::JSValue::asCell(this=0x00007ffeefbfcf78) const at JSCJSValueInlines.h:521 (lldb) p *this (JSC::JSValue) $2 = { u = { asInt64 = -281474976710656 ptr = 0xffff000000000000 asBits = (payload = 0, tag = -65536) } } In this execution, the register rdx contained the value 0xffff000000000000, used in the JITed code as a mask to e.g. quickly determine whether a value is an integer. However, depending on the compiled code, the register could store different (and potentially attacker controlled) data. Moreover, it might be possible to trigger the same misbehaviour in other situations in which the dangling register is expected to hold some other value. This particular sample seems to require the ValueSub DFG instruction, introduced in git commit 5ea7781f2acb639eddc2ec8041328348bdf72877, to produce this type of AIR code. However, it is possible that other DFG IR operations can result in the same AIR code and thus trigger this issue. I have a few other samples that appear to be triggering the same bug with different thresholds and potentially with concurrent JIT enabled which I can share if that is helpful.