Browser Cache

I Know Where You’ve Been: Geo-­‐Inference A6acks via the Browser Cache Yaoqi JIA Department of Computer Science Na2onal University of Singapore Do You Care About your Geo-­‐locaCon? Video:How to Infer Your Geo-­‐
locaCon without Your Consent Our Agenda Ø  Background of geo-­‐loca2ons in browsers, browser cache, and 2ming channels Ø  Geo-­‐inference aBacks via the browser cache Ø  Prevalence of geo-­‐inference aBacks Ø  Pros & cons of poten2al solu2ons Ø  Demo Video for aBacks in TorBrowser Ø  Q & A 4!
Geo-­‐locaCon in Browsers 5!
Geo-­‐locaCon in Browsers 6!
Geo-­‐locaCon in Browsers: Benefits & Threats Benefits Threats 7!
May I Access Your Geo-­‐locaCon? 8!
Sources of Users’ Geo-­‐locaCons Browser Not reliable 9!
Problem Statement ? Browser Can the aBacker infer the user’s geo-­‐loca2on from his browser? 10!
Background: Browser Cache Web Application
①
Network
Module
②
④
Parser
③
Cache
Browser
11!
DirecCves in Response Headers to Control Cache Ø StaCc resources: Ø Expires, Cache-­‐Control: max-­‐age, Last-­‐Modified Ø Dynamic and sensiCve resources: Ø Cache-­‐Control: no-­‐cache, no store; Pragma: no-­‐cache; Expires: 0 12!
Browser Cache Stores StaCc Resources Browser stores site-­‐related states Browser!
13!
Benefits of Browser Cache 1st: 1360ms
2nd: 320ms
3rd: 350ms
Save Time! Browser Cache!
14!
Timing Channels via the Browser Cache 1st: 1360ms
2nd: 320ms
3rd: 350ms
Browser Cache!
15!
Geo-­‐Inference A6acks via the Browser Cache Browser cache is shared across all sites Infer users’ geo-­‐loca2ons! Browser Cache!
16!
Our A6acks: Infer a User’s Geo-­‐locaCon without the Manual Input, Accessing GPS Sensors or IP Addresses 17!
What are the Techniques to Determine the Cache Status of Targeted Resources? 18!
A6ack Vector (I) : Measuring Image Load Time Before Loading img.onload Fires var image = document.createElement(`img');
image.setAttribute(`startTime', (new
Date().getTime()));
image.onload = function()
{
var endTime = new Date().getTime();
var loadTime = endTime parseInt(this.getAttribute(`startTime'));
......
}
aBacker.com 19!
A6ack Vector (II) : Measuring Page Load Time Before Loading iframe.onload Fires var page = document.createElement(`iframe');
page.setAttribute(`startTime', (new
Date()).getTime());
page.onload = function ()
{
var endTime = (new Date()).getTime();
var loadTime = ( endTime parseInt(this.getAttribute(`startTime')));
......
}
aBacker.com 20!
A6ack Vector (III) :Measure the Load Time of XMLH6pRequests onloadstart Fires onloadend Fires var starTime, endTime, loadTime;
var xmlhttp = new XMLHttpRequest();
xmlhttp.onloadstart = function(){
startTime = (new Date()).getTime();
}
xmlhttp.onloadend = function(){
endTime = (new Date()).getTime();
loadTime = endTime - startTime;
......}
aBacker.com 21!
A6ack Vector (IV) : Use <img>’s complete Property function cached(url)
{
var image = document.createElement(`img');
image.src = url;
return image.complete || image.width+image.height >
0;
}
aBacker.com 22!
Examples: What Can We Achieve? Ø User’s country? Ø User’s city? Ø User’s streets or neighborhood? 23!
How to Infer a User’s Country? (I) •  Google has 191 regional sites. •  One site represents one country or region. google.com.sg/images/srpr/
logo11w.png 24!
How to Infer a User’s Country? (II) Cached! Browser Cache!
25!
How to Infer a User’s City? (I) •  Craigslist provides local classifieds adver2sements and forums for jobs, housing, etc. •  Craigslist has 712 city-­‐specific sites. •  Users buy or sell second-­‐hand stuff in their Craigslist’s city-­‐specific sites. 26!
How to Infer a User’s City? (II) chicago.craigslist.org s^ay.craigslist.org newyork.craigslist.org singapore.craigslist. com.sg tokyo.craigslist.jp Cached! Browser Cache!
27!
How to Infer a User’s Neighborhood?(I) Predictable URLs Map Tiles 28!
How to Infer a User’s Neighborhood? (II) Cached! Browser Cache!
29!
EvaluaCon Ques2ons to be answered: Ø (Prevalence) How many websites and browsers can be u2lized to conduct aBacks? Ø (Reliability) How big is the 2me difference between the loading 2me of resources without cache and that with cache? 30!
EvaluaCon Setup Ø Websites: 191 Google’s sites, 100 Craigslist’s sites, and 55 top Alexa sites. Ø Maps: Google Maps, and other 10 map service sites. Ø Browsers: Five mainstream browsers and TorBrowser Ø Loca2ons: US, UK, Australia, Singapore, and Japan. 31!
How Many Websites and Browsers can be UClized to Conduct A6acks? 32!
Alexa Top Websites with LocaCon-­‐Related Resources 62% of 55 top Alexa global sites singapore.craigslist. com.sg sg.yahoo.com www.ebay.com.sg 33!
Map Websites with LocaCon-­‐Related Resources All of 11 map service sites 34!
SuscepCble Browsers & Plaaorms Mainstream Browsers Desktop Plakorms Par2al Mobile Plakorms 35!
How Significant is the Time Difference between the Loading Time of Resources without Cache and that with Cache? 36!
Loading Time: Without Cache v.s. With Cache I 1200 1000 800 Without Cache 600 With Cache 400 200 120ms 1 7 13 19 25 31 37 43 49 55 61 67 73 79 85 91 97 103 109 115 121 127 133 139 145 151 157 163 169 175 181 187 0 Difference in image load /me (in millisecond): Without Cache (> 129 ms) v.s. With Cache (0 ∼ 1 ms), for 191 Google’s regional domains in Chrome on Mac OS X 37!
Loading Time: Without Cache v.s. With Cache II 2000 1500 1000 700ms 500 0 1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64 67 70 73 76 79 82 85 88 91 94 97 100 Without Cache With Cache The significant difference between the page load 2me (in millisecond) of 100 Craigslist sites without cache (> 1000 ms) and with cache (≈ 220 ms) indicates geo-­‐inference aBacks with Craigslist 38!
Loading Time: Without Cache v.s. With Cache III 250 200 150 Without Cache With Cache 100 50 0 1 127 253 379 505 631 757 883 1009 1135 1261 1387 1513 1639 1765 1891 2017 2143 2269 2395 2521 2647 2773 2899 3025 3151 3277 3403 3529 3655 3781 3907 4033 4159 4285 4411 4537 50ms Difference in page load /me (in millisecond): Without Cache (> 50 ms) v.s. With Cache (0 ∼ 1 ms), for 4,646 map 2les of New York City from Google Maps in Chrome on Mac OS X. 39!
Loading Time (Android) 2500 2000 1500 1000 700ms 500 0 1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64 67 70 73 76 79 82 85 88 91 94 97 100 Without Cache With Cache The page load 2me of 100 Craigslist sites on Android. 40!
How to Protect Users from Geo-­‐
inference A6acks Discussion of Defense SoluCons Ø Private Browsing Mode Ø Randomizing 2ming measurements Ø TorBrowser and Segrega2ng browser cache 42!
Private Browsing Mode is not the Cure Private Browsing Mode Ø Clear browser cache aser closing the window. Ø Disable disk cache, not the in-­‐ memory cache. Ø It cannot prevent one site from inferring the user’s geo-­‐loca2on from other sites. Browser Cache!
43!
Randomizing Timing Measurements Ø Add noise into 2ming measurement mechanisms. Ø Affect web applica2ons’ func2onali2es Ø Intricate engineering effort. Browser Cache!
44!
TorBrowser is not Perfect Ø Adds an addi2onal “id=string” property to label every cache entry with the top-­‐level window’s domain. Ø Insufficient for mashup websites, all the embedded sites in frames share the same top-­‐level window’s domain, i.e., the mashup’s domain. Browser Cache!
45!
Demo Video 46!
Video: Geo-­‐inference A6acks in TorBrowser 47!
SegregaCng Browser Cache Ø 400% Deploy Same-­‐Origin Policy on browser cache. 300% Ø We experimented in 200% Chromium 34 Ø 100% High performance overhead for Alexa Top 100 0% 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53 55 57 59 61 63 65 67 69 71 73 75 77 79 81 83 85 87 89 91 93 95 97 websites Browser Cache!
48!
To Cache or Not To Cache? Ø No cache for loca2on-­‐sensi2ve resources (0.7% to 20.7% overhead). Ø Cache-­‐Control: no-­‐cache for HTTP response header Ø Pre-­‐fetch redundant loca2on-­‐sensi2ve resources. Ø Open challenge to design an efficient and secure caching mechanism in browsers. 49!
Take-­‐away Ø  Timing channels are s2ll open on mainstream browsers. Ø  Knowing the power and prevalence of geo-­‐inference aBack (inferring country, city, neighbourhood) and be cau2ous about it. Ø Disable cache? No JavaScript? Ø  Never give addi2onal permissions to unfamiliar sites or open it for a long 2me. Ø  Clear cache before and aser visi2ng a site with your private informa2on, e.g., online banking site. 50!
Yaoqi JIA E-­‐mail: [email protected] References D. Akhawe, A. Barth, P. E. Lam, J. Mitchell, and D. Song, “Towards a formal founda2on of web security,” in Computer Security Founda/ons Symposium (CSF), 2010 23rd IEEE, 2010. A. Bortz and D. Boneh, “Exposing private informa2on by 2ming web applica2ons,” in Proceedings of the 16th interna/onal conference on World Wide Web, 2007. G. Wondracek, T. Holz, E. Kirda, and C. Kruegel, “A prac2cal aBack to de-­‐anonymize social network users,” in Security and Privacy (SP), 2010 IEEE Symposium on, 2010. Z. Weinberg, E. Y. Chen, P. R. Jayaraman, and C. Jackson, “I s2ll know what you visited last summer: Leaking browsing history via user interac2on and side channel aBacks,” in Security and Privacy (SP), 2011 IEEE Symposium on, 2011. M. Jakobsson and S. Stamm, “Invasive browser sniffing and countermeasures,” in Proceedings of the 15th interna/onal conference on World Wide Web, 2006. G. Aggarwal, E. Bursztein, C. Jackson, and D. Boneh, “An analysis of private browsing modes in modern browsers,” in Proceedings of the 19th USENIX Conference on Security, ser. USENIX Security’10, 2010.