1.
• Web
►
• Cross Site Scripting (XSS)
► Web
► Web
► 3
• Client-Side XSS
1

2.
XSS Client-Side XSS
• Client-Side XSS ( : DOM Based XSS) [1]
2[1]. IPA, “IPA DOM Based XSS ”, https://www.ipa.go.jp/files/000024729.pdf , 2013

3.
XSS
3
Client-Side XSS [2]
HTML XSS
Content Security PolicyWeb Application Firewall
[2]. Sebastian Lekies, Krzysztof Kotowicz, Samuel Groß, Eduardo A. Vela Nava, Martin Johns,
“Code-Reuse Attacks for the Web: Breaking Cross-Site Scripting Mitigations via Script Gadgets”, The ACM CCS, 2017
XSS
JavaScript

4.
Client-Side XSS
• Client-Side XSS
► [3]
► [4]
► [5]
► … etc
4
JavaScript Web
[3]. Ben Stock, Sebastian Lekies, Tobias Mueller, Patrick Spiegel, Martin Johns,
“Precise Client-side Protection against DOM-based Cross-Site Scripting”, 23rd USENIX Security Symposium, 2014
[4]. Inian Parameshwaran, Enrico Budianto, Shweta Shinde, “Auto-Patching DOM-based XSS At Scale”,
Proceedings of the 2015 10th Joint Meeting on Foundations of Software Engineering, pp. 272-283, 2015.
[5]. Marius Musch, Marius Steffens, Sebastian Roth, Ben Stock, Martin Johns.
"Scriptprotect: Mitigating unsafe third-party javascript practices", AsiaCCS, 2019.

5.
Trusted Types
• [6]
► Trusted Types
5
$('div').innerHTML = '<img src=/ onerror="alert(10)">' // ERROR
const escapePolicy = TrustedTypes.createPolicy('mypolicy', {
createHTML: (unsafe) => {
return unsafe
.replace(/&/g, "&amp;")
.replace(/</g, "&lt;")
.replace(/>/g, "&gt;")
}
})
const trustedHTML = escapePolicy.createHTML('<img src=/ onerror="alert(10)">')
$('div').innerHTML = trustedHTML // SUCCESS
[6]. Krzysztof Kotowicz, Mike West, "Trusted Types", https://wicg.github.io/trusted-types/dist/spec/
Web

6.
Trusted Types
• 3
►
► Web
► DOM
• Trusted Types JavaScript
►
► Web Web
6

7.
let trusted = "https://example.co.jp/";
let host = location.host;
let hash = location.hash;
document.writeln(trusted); // SUCCESS
document.writeln(host); // ERROR
document.writeln(hash); // ERROR
Trusted Types
• Trusted Types 2
7
1
Trusted Types
let trusted = "https://example.co.jp/";
let host = location.host;
let hash = location.hash;
document.writeln(trusted); // SUCCESS
document.writeln(host); // SUCCESS
document.writeln(hash); // ERROR
Trusted Types
Input Source
URL document.location
baseURI location.hash
documentURI location.search
window.location location.href

8.
• OSS JavaScript Web
► V8: 7.7.299.11
► Chromium: 77.0.3865.90
81 2
let trusted = "https://example.co.jp/";
let host = location.host;
let hash = location.hash;
document.writeln(trusted);
document.writeln(host);
document.writeln(hash);

9.
• JavaScript
•
►
9
Stock
[3]
Parameshwaran
[4] 1 2
Web
×
Web Web
( ) 7~17% 5% 1.2% 0.4~1.2%
0.16% - 46.2% 10.9%

10.
•
► Trusted Types
• 2 URL ? #
10
2 1269 1.1%
))
(
047
12 4 7
36 36 58