Catching IMSI Catchers

Geoffrey Vaughan@mrvaughan

Security Engineer

What you will learn today1. What IMSI Catchers do and how they work2. Detection Strategies3. Hear an exciting tale of adventures in Vegas4. Learn how to avoid being caught up in an IMSI Catcher

Whoami• Geoffrey Vaughan @MrVaughan• Security Engineer @SecurityInnovation• Appsec pentesting/advisory at all areas of SDLC• Former High School/Prison/University Teacher• Occasionally I’m let out of my basement• Travelled from Toronto to be here with you today

IMSI Catchers / StingraysIMSI Catcher:

Can be any rogue cellular device designed to capture cell phone data or traffic

Often used by police/governmentsStingray - Most popular brand of IMSI Catcher sold to police/governments made by Harris Corp

IMSI:International mobile subscriber identity

Your unique cell phone ID.Privacy constraints:

Strict NDA’s often prevent users from disclosing the device capabilities or naming the device publically (even in case of warrants)

IMSI Catcher Specs• Can intercept 2G, 3G, 4G communication

simultaneously as well as CMDA/GSM networks• Devices can launch attacks requesting devices connect

over weaker channels (2G)• Operates in either passive or active mode• Passive mode – Simply captures all available traffic in

the area• Active mode – Acts as a full duplex proxy forcing all

traffic through the device then onward to a normal cellular tower

How they are used• Confirming presence of a device in a target’s home prior to a search thereof• Identifying an individual responsible for sending harassing text messages• Locating a stolen mobile device as a precursor to searching homes in the vicinity• Locating specific individuals by driving around a city until a known IMSI is found• Mounted on airplanes by the United States Marshall Service to sweep entire cities for a

specific mobile device• To monitor all devices within range of a prison to determine whether prisoners are using

cell phones• Reportedly at political protests to identify devices of individuals attending• To monitor activity in the offices of an independent Irish police oversight body

Source: https://citizenlab.org/wp-content/uploads/2016/09/20160818-Report-Gone_Opaque.pdf

Where they are used• 1400+ cases confirmed use in Baltimore mapping show

disproportionate use in predominately black neighborhoods'• http://www.citylab.com/crime/2016/10/racial-disparities-in-poli

ce-stingray-surveillance-mapped/502715/?utm_source=feed

• Thousands of times in Florida since 2007 for crimes as small as 911 hang ups • http://arstechnica.com/tech-policy/2016/08/Baltimore-police-a

ccused-of-illegal-mobile-spectrum-use-with-stingrays/

Manual LeakThe Intercept acquired a device manual and published it:

https://theintercept.com/2016/09/12/long-secret-stingray-manuals-detail-how-police-can-spy-on-phones/

Where to buy• Only sold to governments, police, and military• Alibaba: Good luck (mostly 2G only), Import laws, buyer

assumes risk• But for ~1400USD you can build your own:http://arstechnica.com/security/2015/10/low-cost-imsi-catcher-for-4glte-networks-track-phones-precise-locations/ • Or hide one in a printer and make it call to say I love

youhttps://julianoliver.com/output/stealth-cell-tower

How to find and detect an IMSI CatcherCurrent Detection Methods are entirely anomaly based1. War walk your neighborhood and make note of all Cell

Tower ID’s you find and their locations2. Repeat this until you are sure you have all known

devices cataloged3. Constantly monitor your area to see if any new

devices are added4. Go find the new device

Tools to help you outOpenCellID.org – Database of mostly user reported cellular tower devices, their location, and their identifiersAISMICD – Android IMSI Catcher Detector app. Tool used to collect cell data. It also reports/syncs with OpenCellID (sometimes).• https://github.com/CellularPrivacy/Android-IMSI-Catcher-Detector Rooted Android Device – Required for AISMICD - Means you need a dedicated device for detectionEric Escobar – Detecting Rogue Cell Towers, built a 50$ device to better triangulate devices (Presented this year) • https

://media.defcon.org/DEF%20CON%2024/DEF%20CON%2024%20presentations/DEFCON-24-Eric-Escobar-Rogue-Cell-Towers-UPDATED.pdf

Story Time

How hostile is it for your devices at Def Con?

• Def Con = “Most hostile network on earth” ????• Sure don’t use the hotel Wi Fi but how bad is it for your

cell phones?• Personal experiment to see if I could find any IMSI

Catchers

Setup

• AIMSICD App• Burner Android Phone

(rooted)• Next time: Pre-install

opencellid.org dataWar Driving the Strip in style

Don’t Freak out!Pre Def Con War Walk Post Def Con Data

Lots of false positives• Devices on multiple floors?• Multiple redundant devices in same location• Potential issues with GPS accuracy

Still Unknown Devices

Red dots represent devices that I did not see in my preliminary walk and were not already known to opencellid.org

Caesar’s• 3 Nights in Caesar’s

before Def Con• Lots of towers picked up• Suggest a sort of ‘drive by

attack’• Also observed a lot of LTE

to GSM downgrade attacks, my device was hopping networks quite frequently

Caesar’s• At least 4 of these devices

were previously not known to opencellid.org• There were a couple

others that had only been seen once before

Defense• Depends on your personal threat model• Don’t use your device• Wi Fi calling with vpn?• Signal / OpenWhisper app for calling/SMS, although you

would still be tracked• If all Wireless Carriers published the tower id’s you could at

least know if an id did not match. • Device spoofing would still be possible

• Pressure Wireless Carriers to implement mutual authentication between devices

Conclusions• The devices are very hard to detect, this is part of what

makes them so dangerous• You rarely know when you are connected to these

devices

All data collected is available on my Github Pagehttps://github.com/MrVaughan/Defcon2016GSMData

Shameless Plug• CMD+CTRL CTF Saturday

Night• Accessible web app CTF

for beginners and pros a like • Lots of challenges to keep

you busy• Prizes

Thank youGeoffrey Vaughan@mrvaughan@SecurityInnovation