Why Eve & Mallory Love Android
An Analysis of Android SSL
(In)Security
Android Apps
 Android is the most used Smartphone OS in the
world with 48% market share
 Over 400,000 apps in the Google Play Market
 Android apps have been installed over 10 billion
times
 Apps process a lot of privacy-related user data
and have valid reasons to transmit it over the
internet
Problem
 Apps are not forced to use SSL
 Apps are allowed to customize SSL so many
Android apps use SSL incorrectly and are
vulnerable to MITM attacks
 User has no idea when Android uses SSL
 Users are misinformed about the security of
the connection or misinterpret warning signs
 Able to inject virus code into an antivirus app to
disable virus detection and detect arbitrary apps as a
virus.
 Able to capture credentials from American Express,
Paypal, various bank accounts, Facebook, Twitter,
Google, Yahoo, Microsoft Live ID, etc
Secure Sockets Layer (SSL)
 Used to establish a secure connection between a
client and server.
 Client receives a X.509 certificate containing the
server’s public key that is signed by a certificate
authority.
 Client should validate certificate but this is not yet
required by the SSL and X.509 standards.
SSL Validation Checks
 Does the subject (CN) of the certificate match the
client’s desired destination?
 Is it a trusted Certificate Authority (CA)?
 Is the signature correct?
 Has the certificate expired?
 Has the certificate been revoked?
 Check Certificate Revocation Lists (CRLs)?
 Use Online Certificate Status Protocol (OCSP)?
SSL Misuses in Android
 Trusting all certificates
 Disregards the signer of the certificate and the subject
 Allowing all hostnames
 Does not check if certificate was issued for a given address
 Trusting many Certificate Authorities
 Attacks on CAs in 2011 makes trusting 134 root
authorities questionable
 Mixed-Mode / No SSL
 Can mix secure with insecure connections or use no SSL
Man-in-the-Middle Attacks
 MITMA: an attacker can intercept messages between
conversation partners
 Passive (eavesdropping) vs. active (tampering)
 Mixed-Mode/No SSL allows for passive MITMA by
eavesdropping on non-protected communication or
allowing for SSL stripping
 SSL stripping avoids SSL by replacing https:// with
http://
 Can occur if a browsing session begins using HTTP and
switches to HTTPS via a link or a redirect.
Evaluating Android SSL Usage
 Built MalloDroid to perform static code analysis on 13,500
free apps from Google’s Play Market
 Permissions
 Request INTERNET and other privacy related permissions
 Network API calls
 HTTP transport and Non-HTTP (direct socket connections)
 HTTP vs. HTTPS
 HTTP only, mixed-mode (HTTP and HTTPS), or HTTPS only
 HTTPS available
 Able to establish a secure connection to the HTTP urls?
 Deployed certificates
 Evaluates SSL certificates of hosts referenced in apps
 SSL Validation
Android SSL Usage
 HTTP vs. HTTPS
 74% could have used HTTPS instead of HTTP
 46% mixed-mode, 43% HTTP only, 0.8% HTTPS only
 Deployed SSL Certificates
 17.3% bypass effective SSL verification by accepting all
certificates or all hostnames for a from a trusted CA
 Many apps include HTTPS URLs for hosts that have
certificates that are either expired, self-signed, have
mismatching CNs (site’s common name) or are signed by
non-default-trusted CAs.
MITMA: Trusting All Certificates
 51% use the INTERNET permission in addition to
permissions to access privacy related information
 Trusting all certificates
 Attack: MITMA proxy with self-signed certificate
 Over half of the banking apps tested leaked login
credentials, affecting an install base of 100,000 – half a
million users
 Windows Live Messenger service app with 10-50 million
users leaks login credentials for email, messaging, or
SkyDrive cloud storage
MITMA: Trusting All Hostnames
 Attack: Cert for an unrelated domain signed by startSSL
 Apps, including one used by 82% of Fortune 500 companies,
leaked credentials for sensitive data
 Antivirus app updated virus signatures via broken SSL
 Install base of 500,000 – 1 million users
 Trusted that connection was secure and did no further
validation
 Able to send empty signature database that was accepted
without informing the user
 Able to create a virus signature for the antivirus which
caused it to recognize itself as a virus and delete itself
Overcoming MITMA
 SSL stripping
 Used to go to secure login page from insecure landing page
 Apps with 1.5 million - 6 million installs leak login
credentials for Yahoo, Facebook, and Google
 Overcome by forcing HTTPS
 Lazy SSL
 Poor SSL validation
 Overcome with SSL pinning
 A custom list of trusted CAs or a custom list of specific
certificates
Feedback to Users
 Apps don’t always display visual feedback about whether the
communication is secure.
 Email clients did login and registration in SSL, but sending
and receiving mail defaulted to HTTP without alerting the
user.
 Apps indicate that the connection is secure but are vulnerable
 MITMA when they fail to establish an SSL connection or
do SSL validation
 Replay attack when the logins are encrypted but not fresh
 Apps that did prevent MITMA failed and gave confusing
error messages
Countermeasures: OS Solutions
 Enforced certificate checking
 Disallow custom SSL handling by forcing users to use standard
Android API implementation
 HTTPS everywhere
 Integrated into communication APIs to prevent SSL stripping
 Improved permissions and policies
 Separate permissions for SSL and PLAIN so apps can specify
 Policies like GSM_ONLY, NO_OPEN_WIFI,
TRUSTED_NETWORKS to prevent MITMA
 Visual security feedback
 Properly inform users about connection type and security status.
 MalloDroid installation protection
 Integrated into app installers to warn user of unsafe apps
Countermeasures: Other Solutions
 App Market Solutions
 MalloDroid could be integrated into app market
 Automatically checks apps
 Could prevent apps from entering market or display the
warnings in the app description
 Standalone Solution: The MalloDroid App and
Service
 Easily deployed
 Allows user to perform checks on apps before install
Conclusion
 Google apps handle a lot of personal information for a lot of
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different people
Users wrongly assume, or are incorrectly informed, that they
are transmitting your securely when apps are not required to
use SSL
Apps are vulnerable to MITMA by failing to correctly
validate the SSL certificates or by mixing HTTP with HTTPS
Instead of allowing for SSL customization, proper certificate
validation should be enforced, HTTPS should be used
everywhere, and permissions and policies should be
separated so that apps can better protect users’ data.
Users should be better informed about how secure the
connection is.