CVE-2016-3861 : Detail

CVE-2016-3861

7.8
/
High
Overflow
A01-Broken Access Control
3.55%V3
Local
2016-09-11
19h00 +00:00
2017-09-02
07h57 +00:00
CVE.org
NVD
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CVE Descriptions

LibUtils in Android 4.x before 4.4.4, 5.0.x before 5.0.2, 5.1.x before 5.1.1, 6.x before 2016-09-01, and 7.0 before 2016-09-01 mishandles conversions between Unicode character encodings with different encoding widths, which allows remote attackers to execute arbitrary code or cause a denial of service (heap-based buffer overflow) via a crafted file, aka internal bug 29250543.

CVE Informations

Related Weaknesses

CWE-ID Weakness Name Source
CWE-119 Improper Restriction of Operations within the Bounds of a Memory Buffer
The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.
CWE-264 Category : Permissions, Privileges, and Access Controls
Weaknesses in this category are related to the management of permissions, privileges, and other security features that are used to perform access control.

Metrics

Metrics Score Severity CVSS Vector Source
V3.0 7.8 HIGH CVSS:3.0/AV:L/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.

Local

A vulnerability exploitable with Local access means that the vulnerable component is not bound to the network stack, and the attacker's path is via read/write/execute capabilities. In some cases, the attacker may be logged in locally in order to exploit the vulnerability, otherwise, she may rely on User Interaction to execute a malicious file.

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

 [email protected]
V2 9.3 AV:N/AC:M/Au:N/C:C/I:C/A:C [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 : 40354

Publication date : 2016-09-07 22h00 +00:00
Author : Google Security Research
EDB Verified : Yes

Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=840 There's an inconsistency between the way that the two functions in libutils/Unicode.cpp handle invalid surrogate pairs in UTF16, resulting in a mismatch between the size calculated by utf16_to_utf8_length and the number of bytes written by utf16_to_utf8. This results in a heap-buffer-overflow; one route to this code is the String8 constructor initialising a String8 from a String16. This can be reached via binder calls to the core system service "android.security.keystore" from a normal app context without any additional permissions. There are probably other routes to reach this code with attacker controlled data. ssize_t utf16_to_utf8_length(const char16_t *src, size_t src_len) { if (src == NULL || src_len == 0) { return -1; } size_t ret = 0; const char16_t* const end = src + src_len; while (src < end) { if ((*src & 0xFC00) == 0xD800 && (src + 1) < end && (*++src & 0xFC00) == 0xDC00) { // <---- increment src here even if condition is false // surrogate pairs are always 4 bytes. ret += 4; src++; } else { ret += utf32_codepoint_utf8_length((char32_t) *src++); // <---- increment src again } } return ret; } void utf16_to_utf8(const char16_t* src, size_t src_len, char* dst) { if (src == NULL || src_len == 0 || dst == NULL) { return; } const char16_t* cur_utf16 = src; const char16_t* const end_utf16 = src + src_len; char *cur = dst; while (cur_utf16 < end_utf16) { char32_t utf32; // surrogate pairs if((*cur_utf16 & 0xFC00) == 0xD800 && (cur_utf16 + 1) < end_utf16 && (*(cur_utf16 + 1) & 0xFC00) == 0xDC00) { // <---- no increment if condition is false utf32 = (*cur_utf16++ - 0xD800) << 10; utf32 |= *cur_utf16++ - 0xDC00; utf32 += 0x10000; } else { utf32 = (char32_t) *cur_utf16++; // <---- increment src } const size_t len = utf32_codepoint_utf8_length(utf32); utf32_codepoint_to_utf8((uint8_t*)cur, utf32, len); cur += len; } *cur = '\0'; } An example character sequence would be the following: \x41\xd8 \x41\xd8 \x41\xdc \x00\x00 This will be processed by utf16_to_utf8_len like this: first loop iteration: \x41\xd8 \x41\xd8 \x41\xdc \x00\x00 ^ invalid surrogate; skip at (*++src & 0xfc00 == 0xdc00) \x41\xd8 \x41\xd8 \x41\xdc \x00\x00 ^ invalid surrogate; emit length 0 at (utf32_codepoint_utf8_length(*src++)) second loop iteration: \x41\xd8 \x41\xd8 \x41\xdc \x00\x00 ^ invalid surrogate; emit length 0 at (utf32_codepoint_utf8_length(*src++)) And will be processed by utf16_to_utf8 like this: first loop iteration: \x41\xd8 \x41\xd8 \x41\xdc \x00\x00 ^ invalid surrogate; write 0 length character to output second loop iteration \x41\xd8 \x41\xd8 \x41\xdc \x00\x00 ^ valid surrogate pair 0xd841 0xdc41; emit length 4 character to output We can then construct a crash PoC using this sequence for the String16 passed to the keystore method 'getKeyCharacteristics' that will perform the String8(String16&) constructor on attacker supplied input; and provide a massive input string. The crash PoC should write 0x20000 * 2/3 bytes into a 2 byte heap allocation. It has been tested on a recent nexus5x userdebug build; resulting in the following crash (the object backing an android::vectorImpl has been corrupted by the overwrite, and "\xf0\xa0\x91\x81" is the utf8 encoding for the utf16 "\x41\xd8 \x41\xdc"): pid: 16669, tid: 16669, name: keystore >>> /system/bin/keystore <<< signal 11 (SIGSEGV), code 1 (SEGV_MAPERR), fault addr 0x91a0f08191a110 x0 8191a0f08191a108 x1 0000000000000000 x2 0000000000000000 x3 0000000000000020 x4 00000000ffffffa0 x5 0000000000000010 x6 0000000000000001 x7 0000007f802c0018 x8 0000000000000000 x9 000000000a7c5ac5 x10 0000000000000000 x11 0000000000000000 x12 000000000000d841 x13 0000000000000841 x14 0000000000000041 x15 0000007f8067bd9e x16 0000005565984f08 x17 0000007f80aeee48 x18 00000000ffffff91 x19 0000007fd1de26c0 x20 8191a0f08191a108 x21 8191a0f08191a0f0 x22 0000000000000000 x23 0000005565984000 x24 8191a0f08191a0f0 x25 0000007fd1dea7b8 x26 0000007f806690e0 x27 0000007fd1de25d0 x28 000000556596f000 x29 0000007fd1de2550 x30 0000005565961188 sp 0000007fd1de2550 pc 0000007f80aeee58 pstate 0000000060000000 backtrace: #00 pc 0000000000016e58 /system/lib64/libutils.so (_ZN7android10VectorImpl13editArrayImplEv+16) #01 pc 000000000000a184 /system/bin/keystore #02 pc 00000000000112d0 /system/bin/keystore #03 pc 000000000000b7f4 /system/lib64/libkeystore_binder.so (_ZN7android17BnKeystoreService10onTransactEjRKNS_6ParcelEPS1_j+1560) #04 pc 0000000000024c9c /system/lib64/libbinder.so (_ZN7android7BBinder8transactEjRKNS_6ParcelEPS1_j+168) #05 pc 000000000002dd98 /system/lib64/libbinder.so (_ZN7android14IPCThreadState14executeCommandEi+1240) #06 pc 000000000002de4c /system/lib64/libbinder.so (_ZN7android14IPCThreadState20getAndExecuteCommandEv+140) #07 pc 000000000002def4 /system/lib64/libbinder.so (_ZN7android14IPCThreadState14joinThreadPoolEb+76) #08 pc 0000000000007a04 /system/bin/keystore (main+1940) #09 pc 000000000001bc98 /system/lib64/libc.so (__libc_init+100) #10 pc 0000000000007c20 /system/bin/keystore ###################################################### Actually you can compromise many native system services using this bug (ie those not implemented in Java); because of the interface token checking code in Parcel.cpp. See attached for another PoC that takes as a first command line argument the name of the service to crash. On my nexus 5x with very unscientific testing, this includes the following services: - phone, iphonesubinfo, isub (com.android.phone) - telecom, voiceinteraction, backup, audio, location, notification, connectivity, wifi, network_management, statusbar, device_policy, mount, input_method, window, content, account, telephony.registry, user, package, batterystats (system_server) - media.audio_policy, media.audio_flinger (mediaserver) - drm.drmManager (drmserver) - android.security.keystore (keystore) - SurfaceFlinger (surfaceflinger) bool Parcel::enforceInterface(const String16& interface, IPCThreadState* threadState) const { int32_t strictPolicy = readInt32(); if (threadState == NULL) { threadState = IPCThreadState::self(); } if ((threadState->getLastTransactionBinderFlags() & IBinder::FLAG_ONEWAY) != 0) { // For one-way calls, the callee is running entirely // disconnected from the caller, so disable StrictMode entirely. // Not only does disk/network usage not impact the caller, but // there's no way to commuicate back any violations anyway. threadState->setStrictModePolicy(0); } else { threadState->setStrictModePolicy(strictPolicy); } const String16 str(readString16()); if (str == interface) { return true; } else { ALOGW("**** enforceInterface() expected '%s' but read '%s'", String8(interface).string(), String8(str).string()); return false; } } Proofs of Concept: https://gitlab.com/exploit-database/exploitdb-bin-sploits/-/raw/main/bin-sploits/40354.zip

Products Mentioned

Configuraton 0

Google>>Android >> Version 4.0

Google>>Android >> Version 4.0.1

Google>>Android >> Version 4.0.2

Google>>Android >> Version 4.0.3

Google>>Android >> Version 4.0.4

Google>>Android >> Version 4.1

Google>>Android >> Version 4.1.2

Google>>Android >> Version 4.2

Google>>Android >> Version 4.2.1

Google>>Android >> Version 4.2.2

Google>>Android >> Version 4.3

Google>>Android >> Version 4.3.1

Google>>Android >> Version 4.4

Google>>Android >> Version 4.4.1

Google>>Android >> Version 4.4.2

Google>>Android >> Version 4.4.3

Google>>Android >> Version 5.0

Google>>Android >> Version 5.0.1

Google>>Android >> Version 5.1

Google>>Android >> Version 5.1.0

Google>>Android >> Version 6.0

Google>>Android >> Version 6.0.1

Google>>Android >> Version 7.0

References

http://www.securitytracker.com/id/1036763
Tags : vdb-entry, x_refsource_SECTRACK
http://www.securityfocus.com/bid/92811
Tags : vdb-entry, x_refsource_BID
https://www.exploit-db.com/exploits/40354/
Tags : exploit, x_refsource_EXPLOIT-DB