fabian19941220-gmail-com / salvation

Parse Content Security Policy headers, warn about policy errors, safely manipulate, render, and optimise policies

salvation

This is a general purpose library for working with Content Security Policy policies.

• parse CSP policies into an easy-to-use representation
• ask questions about what a CSP policy allows or restricts
• warn about nonsensical CSP policies and deprecated or nonstandard features
• safely create, manipulate, and merge CSP policies
• render and optimise CSP policies

cspvalidator.org demonstrates some of the features of Salvation in action.

Install

mvn install

Create a Policy

Parse a policy using one of the Parser.parse static methods. An Origin or String may be given as the origin. The third parameter, if given, will be populated with notices.

ArrayList<Notice> notices = new ArrayList<>();
Origin origin = URI.parse("http://example.com");
String policyText = "...";
Policy p = Parser.parse(policyText, origin, notices);

To include location information, use ParserWithLocation.parse in place of Parser.parse.

ArrayList<Notice> notices = new ArrayList<>();
ParserWithLocation.parse("image-src *; script-src none; report-uri /report", "https://example.com", notices);

Notice.getAllErrors(notices).get(0).show(); 
// 1:1: Unrecognised directive-name: "image-src".

Notice.getAllWarnings(notices).get(0).show();
// 1:25: This host name is unusual, and likely meant to be a keyword that is missing the required quotes: 'none'.

Notice.getAllInfos(notices).get(0).show(); 
// 1:31: A draft of the next version of CSP deprecates report-uri in favour of a new report-to directive.

A policy may also be created using the Policy constructor and populated using the addDirective method.

Origin origin = URI.parse("http://example.com");
Policy p = new Policy(origin);
Set<SourceExpression> scriptSourceValues = new HashSet<>();
scriptSourceValues.add(None.INSTANCE;
p.addDirective(new ScriptSrcDirective(scriptSourceValues));

Query a Policy

Policy p = Parser.parse("script-src a; default-src b", "http://example.com");
p.allowsScriptFromSource(URI.parse("http://a")); // true
p.allowsScriptFromSource(URI.parse("http://b")); // false
p.allowsStyleFromSource(URI.parse("http://b")); // true

Perform source-expression-specific queries and manipulations:

Policy p = Parser.parse("default-src *.example.com 'unsafe-inline' 'nonce-123' 'strict-dynamic'", "http://example.com");
p.containsSourceExpression(ScriptSrcDirective.class, x -> x == KeywordSource.UnsafeInline)); // true
p.allowsUnsafeInlineScript(); // false
p.getEffectiveSourceExpressions(ScriptSrcDirective.class).filter(x -> x instanceof HostSource).count(); // 1

Manipulate Policies

Intersection merge:

Policy p = Parser.parse("script-src a; default-src b", "http://example.com");
Policy q = Parser.parse("script-src b;", "http://example.com");
p.intersect(q);
p.show(); // script-src; default-src b

Union merge:

Policy p = Parser.parse("script-src a; default-src b", "http://example.com");
Policy q = Parser.parse("script-src b;", "http://example.com");
p.union(q);
p.show(); // script-src a b