An investigation of Chrysaor Malware on Android

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Posted by Rich Cannings, Jason Woloz, Neel Mehta, Ken Bodzak, Wentao Chang, Megan Ruthven

Google is constantly working to improve our systems that protect users from Potentially
Harmful Applications (PHAs). Usually, PHA authors attempt to install their
harmful apps on as many devices as possible. However, a few PHA authors spend
substantial effort, time, and money to create and install their harmful app on
one or a very small number of devices. This is known as a targeted attack.

In this blog post, we describe Chrysaor, a newly discovered family of spyware
that was used in a targeted attack on a small number of Android devices, and how
investigations like this help Google protect Android users from a variety of

What is Chrysaor?

Chrysaor is spyware believed to be created by NSO Group Technologies,
specializing in the creation and sale of software and infrastructure for
targeted attacks. Chrysaor is believed to be related to the Pegasus spyware that
was first
identified on iOS and analyzed by Citizen
Lab and Lookout.

Late last year, after receiving a list of suspicious package names from Lookout,
we discovered that a few dozen Android devices may have installed an application
related to Pegasus, which we named Chrysaor. Although the applications were
never available in Google Play, we immediately identified the scope of the
problem by using Verify Apps.
We gathered information from affected devices, and concurrently, attempted to
acquire Chrysaor apps to better understand its impact on users. We’ve contacted
the potentially affected users, disabled the applications on affected devices,
and implemented changes in Verify Apps to protect all users.

What is the scope of Chrysaor?

Chrysaor was never available in Google Play and had a very low volume of
installs outside of Google Play. Among the over 1.4 billion devices protected by
Verify Apps, we observed fewer than 3 dozen installs of Chrysaor on victim
devices. These devices were located in the following countries:

How we protect you

To protect Android devices and users, Google Play provides a complete set of
security services that update outside of platform releases. Users don’t have to
install any additional security services to keep their devices safe. In 2016,
these services protected over 1.4 billion devices, making Google one of the
largest providers of on-device security services in the world:

  • Identify
    PHAs using people, systems in the cloud, and data sent to us from devices
  • Warn users
    about or blocking users from installing PHAs
  • Continually
    scan devices for PHAs and other harmful threats

Additionally, we are providing detailed technical information to help the
security industry in our collective work against PHAs.

What do I need to do?

It is extremely unlikely you or someone you know was affected by Chrysaor
malware. Through our investigation, we identified less than 3 dozen devices
affected by Chrysaor, we have disabled Chrysaor on those devices, and we have
notified users of all known affected devices. Additionally, the improvements we
made to our protections have been enabled for all users of our security

To ensure you are fully protected against PHAs and other threats, we recommend
these 5 basic steps:

  • Install apps only from reputable sources: Install apps from
    a reputable source, such as Google Play. No
    Chrysaor apps were on Google Play.
  • Enable a
    secure lock screen
    : Pick a PIN, pattern, or password that is easy
    for you to remember and hard for others to guess.
  • Update
    your device
    : Keep your device up-to-date with the latest security
  • Verify
    Ensure Verify Apps is enabled.
  • Locate your device: Practice finding your device with Android Device Manager
    because you are far more likely to lose your device than install a

How does Chrysaor work?

To install Chrysaor, we believe an attacker coaxed specifically targeted
individuals to download the malicious software onto their device. Once Chrysaor
is installed, a remote operator is able to surveil the victim’s activities on
the device and within the vicinity, leveraging microphone, camera, data
collection, and logging and tracking application activities on communication
apps such as phone and SMS.

One representative sample Chrysaor app that we analyzed was tailored to devices
running Jellybean (4.3) or earlier. The following is a review of scope and
impact of the Chrysaor app named tailored for a
Samsung device target, with SHA256 digest:


Upon installation, the app uses known framaroot exploits to escalate privileges
and break Android’s application sandbox. If the targeted device is not
vulnerable to these exploits, then the app attempts to use a superuser binary
pre-positioned at /system/csk to elevate privileges.

After escalating privileges, the app immediately protects itself and starts to
collect data, by:

  • Installing itself on the /system partition to persist across
    factory resets
  • Removing Samsung’s system update app
    ( and disabling auto-updates to maintain
    persistence (sets Settings.System.SOFTWARE_UPDATE_AUTO_UPDATE to 0)
  • Deleting WAP push messages and changing WAP message settings, possibly for
    anti-forensic purpose.
  • Starting content observers and the main task loop to receive remote commands
    and exfiltrate data

The app uses six techniques to collect user data:

  • Repeated commands: use alarms to periodically repeat
    actions on the device to expose data, including gathering location data.
  • Data collectors: dump all existing content on the device
    into a queue. Data collectors are used in conjunction with repeated commands to
    collect user data including, SMS settings, SMS messages, Call logs, Browser
    History, Calendar, Contacts, Emails, and messages from selected messaging apps,
    including WhatsApp, Twitter, Facebook, Kakoa, Viber, and Skype by making
    /data/data directories of the apps world readable.
  • Content observers: use Android’s ContentObserver
    framework to gather changes in SMS, Calendar, Contacts, Cell info, Email,
    WhatsApp, Facebook, Twitter, Kakao, Viber, and Skype.
  • Screenshots: captures an image of the current screen via
    the raw frame buffer.
  • Keylogging: record input events by hooking
    IPCThreadState::Transact from
    /system/lib/, and intercepting android::parcel with the
  • RoomTap: silently answers a telephone call and stays
    connected in the background, allowing the caller to hear conversations within
    the range of the phone’s microphone. If the user unlocks their device, they will
    see a black screen while the app drops the call, resets call settings and
    prepares for the user to interact with the device normally.

Finally, the app can remove itself through three ways:

  • Via a command from the server
  • Autoremove if the device has not been able to check in to the server after
    60 days
  • Via an antidote file. If /sdcard/MemosForNotes was present on
    the device, the Chrysaor app removes itself from the device.

Samples uploaded to VirusTotal

To encourage further research in the security community, we’ve uploaded these sample Chrysaor apps to Virus Total.

Package Name
SHA256 digest
SHA1 certificate

Additional digests with links to Chrysaor

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As a result of our investigation we have identified these additional Chrysaor-related apps.

Package Name
SHA256 digest
SHA1 certificate
Lookout has completed their own independent analysis of the samples we acquired, their report can be viewed here.

Android Developers Blog

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