Google Android up to 4.2 APK Package Signature cryptographic issues

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A vulnerability classified as critical has been found in Google Android (Smartphone Operating System). This affects an unknown code block of the component APK Package Signature Handler. The manipulation with an unknown input leads to a weak encryption vulnerability. CWE is classifying the issue as CWE-310. This is going to have an impact on confidentiality, integrity, and availability. The summary by CVE is:

Android 1.6 Donut through 4.2 Jelly Bean does not properly check cryptographic signatures for applications, which allows attackers to execute arbitrary code via an application package file (APK) that is modified in a way that does not violate the cryptographic signature, probably involving multiple entries in a Zip file with the same name in which one entry is validated but the other entry is installed, aka Android security bug 8219321 and the "Master Key" vulnerability.

The weakness was published 07/03/2013 by Jeff Forristal with Bluebox Security as Android Security Bug 8219321 as not defined blog post (Website). It is possible to read the advisory at The public release has been coordinated with Google. The blog post contains:

[A] vulnerability in Android’s security model that allows a hacker to modify APK code without breaking an application’s cryptographic signature, to turn any legitimate application into a malicious Trojan, completely unnoticed by the app store, the phone, or the end user. (…) This vulnerability, around at least since the release of Android 1.6 (codename: “Donut” ), could affect any Android phone released in the last 4 years – or nearly 900 million devices – and depending on the type of application, a hacker can exploit the vulnerability for anything from data theft to creation of a mobile botnet.
Technical details of the issue, and related tools/material, will be released as part of a Black Hat USA 2013 talk. This vulnerability is uniquely identified as CVE-2013-4787 since 07/09/2013. It is possible to initiate the attack remotely. No form of authentication is needed for exploitation. Technical details are unknown but a public exploit is available. The pricing for an exploit might be around USD $0-$5k at the moment (estimation calculated on 05/14/2017). It is expected to see the exploit prices for this product increasing in the near future.Due to its background and reception, this vulnerability has a historic impact. The advisory points out:
All Android applications contain cryptographic signatures, which Android uses to determine if the app is legitimate and to verify that the app hasn’t been tampered with or modified. This vulnerability makes it possible to change an application’s code without affecting the cryptographic signature of the application – essentially allowing a malicious author to trick Android into believing the app is unchanged even if it has been.

A public exploit has been developed by Jeff Forristal and been published 2 months after the advisory. It is declared as proof-of-concept. The exploit is shared for download at We expect the 0-day to have been worth approximately $25k-$100k. The real existence of this vulnerability is still doubted at the moment. The advisory illustrates:

Installation of a Trojan application from the device manufacturer can grant the application full access to Android system and all applications (and their data) currently installed. The application then not only has the ability to read arbitrary application data on the device (email, SMS messages, documents, etc.), retrieve all stored account & service passwords, it can essentially take over the normal functioning of the phone and control any function thereof (make arbitrary phone calls, send arbitrary SMS messages, turn on the camera, and record calls). Finally, and most unsettling, is the potential for a hacker to take advantage of the always-on, always-connected, and always-moving (therefore hard-to-detect) nature of these “zombie” mobile devices to create a botnet.
Working PoCs for major Android device vendors will be made available to coincide with the presentation at Black Hat USA 2013.

Upgrading to version 2013-07-07 eliminates this vulnerability. Applying a patch is able to eliminate this problem. The problem might be mitigated by replacing the product with Apple iOS or Microsoft Windows Phone as an alternative. The best possible mitigation is suggested to be patching the affected component. A possible mitigation has been published even before and not after the disclosure of the vulnerability. The blog post contains the following remark:

It’s up to device manufacturers to produce and release firmware updates for mobile devices (and furthermore for users to install these updates). The availability of these updates will widely vary depending upon the manufacturer and model in question.

The vulnerability is also documented in the databases at SecurityFocus (BID 60952), X-Force (85500) and Vulnerability Center (SBV-42084). Further details are available at Similar entry is available at 9515.





CPE 2.3infoedit

CPE 2.2infoedit



VulDB Meta Base Score: 8.1
VulDB Meta Temp Score: 7.3

VulDB Base Score: 8.1
VulDB Temp Score: 7.3
VulDB Vector: 🔍
VulDB Reliability: 🔍



VulDB Base Score: 🔍
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NVD Base Score: 🔍


Class: Weak encryption (CWE-310)
Local: No
Remote: Yes

Availability: 🔍
Access: Public
Status: Proof-of-Concept
Author: Jeff Forristal
Download: 🔍

Price Prediction: 🔍
Current Price Estimation: 🔍


Threat Intelligenceinfoedit

Threat: 🔍
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Recommended: Patch
Status: 🔍

0-Day Time: 🔍
Exploit Delay Time: 🔍

Upgrade: Android 2013-07-07
Alternative: Apple iOS/Microsoft Windows Phone


02/01/2013 🔍
07/03/2013 +152 days 🔍
07/03/2013 +0 days 🔍
07/04/2013 +1 days 🔍
07/09/2013 +5 days 🔍
07/09/2013 +0 days 🔍
08/01/2013 +23 days 🔍
10/24/2013 +84 days 🔍
04/21/2017 +1275 days 🔍
05/14/2017 +23 days 🔍



Advisory: Android Security Bug 8219321
Researcher: Jeff Forristal
Organization: Bluebox Security
Status: Not defined
Coordinated: 🔍
Disputed: 🔍

CVE: CVE-2013-4787 (🔍)
SecurityFocus: 60952
X-Force: 85500
Vulnerability Center: 42084 - Google Android 1.6 - 4.2 Remote Code Execution Vulnerability Using Master Key to Change APK Code, Critical
OSVDB: 94773

scip Labs:
Misc.: 🔍
See also: 🔍


Created: 07/04/2013 11:22 AM
Updated: 05/14/2017 09:34 AM
Changes: (18) software_type vulnerability_cwe vulnerability_cvss2_nvd_av vulnerability_cvss2_nvd_ac vulnerability_cvss2_nvd_au vulnerability_cvss2_nvd_ci vulnerability_cvss2_nvd_ii vulnerability_cvss2_nvd_ai source_cve_assigned source_cve_nvd_published source_cve_nvd_summary source_securityfocus source_vulnerabilitycenter source_vulnerabilitycenter_title source_vulnerabilitycenter_severity source_vulnerabilitycenter_creationdate source_vulnerabilitycenter_lastupdatedate source_vulnerabilitycenter_reportingdate
Complete: 🔍


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