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A library for performing fast, configurable cleansing of HTML coming from untrusted sources.
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/*
* Copyright (c) 2007-2022, Arshan Dabirsiaghi, Jason Li
*
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
* - Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
* - Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
* - Neither the name of OWASP nor the names of its contributors may be used to
* endorse or promote products derived from this software without specific
* prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
package org.owasp.validator.css;
import java.util.Iterator;
import java.util.regex.Pattern;
import org.owasp.validator.html.Policy;
import org.owasp.validator.html.ScanException;
import org.owasp.validator.html.model.AntiSamyPattern;
import org.owasp.validator.html.model.Property;
import org.owasp.validator.html.util.HTMLEntityEncoder;
import org.w3c.css.sac.AttributeCondition;
import org.w3c.css.sac.CombinatorCondition;
import org.w3c.css.sac.Condition;
import org.w3c.css.sac.ConditionalSelector;
import org.w3c.css.sac.DescendantSelector;
import org.w3c.css.sac.LexicalUnit;
import org.w3c.css.sac.NegativeCondition;
import org.w3c.css.sac.NegativeSelector;
import org.w3c.css.sac.Selector;
import org.w3c.css.sac.SiblingSelector;
import org.w3c.css.sac.SimpleSelector;
/**
* Encapsulates all the necessary operations for validating individual elements of a stylesheet
* (namely: selectors, conditions, and properties).
*
* @author Jason Li
*/
public class CssValidator {
private final Policy policy;
/**
* Constructs a validator for CSS selectors, conditions, and properties based on the given
* AntiSamy policy.
*
* @param policy the policy file to use with this validator
*/
public CssValidator(Policy policy) {
this.policy = policy;
}
/**
* Determines whether the given property (both name and value) are valid according to this
* validator's policy.
*
* @param name the name of the property
* @param lu the value of the property
* @return true if this property name/value is valid; false otherwise
*/
public boolean isValidProperty(String name, LexicalUnit lu) {
boolean isValid = false;
Property property = null;
if (name != null) {
property = policy.getPropertyByName(name.toLowerCase());
}
// if we were able to find the property by name, validate the value
if (property != null) {
// validate all values attached to this property
isValid = true;
while (lu != null) {
String value = lexicalValueToString(lu);
if (value == null || !validateValue(property, value)) {
isValid = false;
break;
}
lu = lu.getNextLexicalUnit();
}
}
return isValid;
}
/**
* Determines whether the given selector name is valid according to this validator's policy.
*
* @param selectorName the name of the selector
* @param selector the object representation of the selector
* @return true if this selector name is valid; false otherwise
* @throws ScanException When there is a problem encountered while scanning this selector
*/
public boolean isValidSelector(String selectorName, Selector selector) throws ScanException {
// determine correct behavior
switch (selector.getSelectorType()) {
case Selector.SAC_ANY_NODE_SELECTOR:
case Selector.SAC_ELEMENT_NODE_SELECTOR:
case Selector.SAC_PSEUDO_ELEMENT_SELECTOR:
case Selector.SAC_ROOT_NODE_SELECTOR:
// these selectors are the most base selectors
return validateSimpleSelector((SimpleSelector) selector);
case Selector.SAC_CHILD_SELECTOR:
case Selector.SAC_DESCENDANT_SELECTOR:
// these are compound selectors - decompose into simple selectors
DescendantSelector descSelector = (DescendantSelector) selector;
return isValidSelector(selectorName, descSelector.getSimpleSelector())
&& isValidSelector(selectorName, descSelector.getAncestorSelector());
case Selector.SAC_CONDITIONAL_SELECTOR:
// this is a compound selector - decompose into simple selectors
ConditionalSelector condSelector = (ConditionalSelector) selector;
return isValidSelector(selectorName, condSelector.getSimpleSelector())
&& isValidCondition(selectorName, condSelector.getCondition());
case Selector.SAC_DIRECT_ADJACENT_SELECTOR:
// this is a compound selector - decompose into simple selectors
SiblingSelector sibSelector = (SiblingSelector) selector;
return isValidSelector(selectorName, sibSelector.getSiblingSelector())
&& isValidSelector(selectorName, sibSelector.getSelector());
case Selector.SAC_NEGATIVE_SELECTOR:
// this is a compound selector with one simple selector
return validateSimpleSelector((NegativeSelector) selector);
case Selector.SAC_CDATA_SECTION_NODE_SELECTOR:
case Selector.SAC_COMMENT_NODE_SELECTOR:
case Selector.SAC_PROCESSING_INSTRUCTION_NODE_SELECTOR:
case Selector.SAC_TEXT_NODE_SELECTOR:
default:
throw new UnknownSelectorException(HTMLEntityEncoder.htmlEntityEncode(selector.toString()));
}
}
/**
* Validates a basic selector against the policy
*
* @param selector the object representation of the selector
* @return true if this selector name is valid; false otherwise
*/
private boolean validateSimpleSelector(SimpleSelector selector) {
// ensure the name follows the valid pattern and is not blacklisted
// by the exclusion pattern.
// NOTE: intentionally using non-short-circuited AND operator to
// generate all relevant error messages
String selectorLowerCase = selector.toString().toLowerCase();
return policy.getCommonRegularExpressions("cssElementSelector").matches(selectorLowerCase)
&& !policy.getCommonRegularExpressions("cssElementExclusion").matches(selectorLowerCase);
}
/**
* Determines whether the given condition is valid according to this validator's policy.
*
* @param selectorName the name of the selector that contains this condition
* @param condition the object representation of this condition
* @return true if this condition is valid; false otherwise
* @throws ScanException When there is a problem encountered while scanning this condition
*/
public boolean isValidCondition(String selectorName, Condition condition) throws ScanException {
switch (condition.getConditionType()) {
case Condition.SAC_AND_CONDITION:
case Condition.SAC_OR_CONDITION:
// these are compound condition - decompose into simple conditions
CombinatorCondition comboCondition = (CombinatorCondition) condition;
return isValidCondition(selectorName, comboCondition.getFirstCondition())
&& isValidCondition(selectorName, comboCondition.getSecondCondition());
case Condition.SAC_CLASS_CONDITION:
// this is a basic class condition; compare condition against
// valid pattern and is not blacklisted by exclusion pattern
return validateCondition(
(AttributeCondition) condition,
policy.getCommonRegularExpressions("cssClassSelector"),
policy.getCommonRegularExpressions("cssClassExclusion"));
case Condition.SAC_ID_CONDITION:
// this is a basic ID condition; compare condition against
// valid pattern and is not blacklisted by exclusion pattern
return validateCondition(
(AttributeCondition) condition,
policy.getCommonRegularExpressions("cssIDSelector"),
policy.getCommonRegularExpressions("cssIDExclusion"));
case Condition.SAC_PSEUDO_CLASS_CONDITION:
// this is a basic psuedo element condition; compare condition
// against valid pattern and is not blacklisted by exclusion pattern
return validateCondition(
(AttributeCondition) condition,
policy.getCommonRegularExpressions("cssPseudoElementSelector"),
policy.getCommonRegularExpressions("cssPsuedoElementExclusion"));
case Condition.SAC_BEGIN_HYPHEN_ATTRIBUTE_CONDITION:
case Condition.SAC_ONE_OF_ATTRIBUTE_CONDITION:
case Condition.SAC_ATTRIBUTE_CONDITION:
// this is a basic class condition; compare condition against
// valid pattern and is not blacklisted by exclusion pattern
return validateCondition(
(AttributeCondition) condition,
policy.getCommonRegularExpressions("cssAttributeSelector"),
policy.getCommonRegularExpressions("cssAttributeExclusion"));
case Condition.SAC_NEGATIVE_CONDITION:
// this is a compound condition; decompose to simple condition
return isValidCondition(selectorName, ((NegativeCondition) condition).getCondition());
case Condition.SAC_ONLY_CHILD_CONDITION:
case Condition.SAC_ONLY_TYPE_CONDITION:
// :only-child and :only-of-type are constants
return true;
case Condition.SAC_POSITIONAL_CONDITION:
case Condition.SAC_CONTENT_CONDITION:
case Condition.SAC_LANG_CONDITION:
default:
throw new UnknownSelectorException(HTMLEntityEncoder.htmlEntityEncode(selectorName));
}
}
/**
* Validates a basic condition against the white list pattern and the blacklist pattern
*
* @param condition the object representation of the condition
* @param pattern the positive pattern of valid conditions
* @param exclusionPattern the negative pattern of excluded conditions
* @return true if this selector name is valid; false otherwise
*/
private boolean validateCondition(
AttributeCondition condition, AntiSamyPattern pattern, AntiSamyPattern exclusionPattern) {
// check that the name of the condition matches valid pattern and does
// not match exclusion pattern
// NOTE: intentionally using non-short-circuited AND operator to
// generate all relevant error messages
String otherLower = condition.toString().toLowerCase();
return pattern.matches(otherLower) && !exclusionPattern.matches(otherLower);
}
/**
* Determines whether the given property value is valid according to this validator's policy.
*
* @param property the object representation of the property and its associated policy
* @param value the string representation of the value
* @return true if the property is valid; false otherwise
*/
private boolean validateValue(Property property, String value) {
boolean isValid = false;
// normalize the value to lowercase
value = value.toLowerCase();
// check if the value matches any of the allowed literal values
Iterator allowedValues = property.getAllowedValues().iterator();
while (allowedValues.hasNext() && !isValid) {
String allowedValue = (String) allowedValues.next();
if (allowedValue != null && allowedValue.equals(value)) {
isValid = true;
}
}
// check if the value matches any of the allowed regular expressions
Iterator allowedRegexps = property.getAllowedRegExp().iterator();
while (allowedRegexps.hasNext() && !isValid) {
Pattern pattern = (Pattern) allowedRegexps.next();
if (pattern != null && pattern.matcher(value).matches()) {
isValid = true;
}
}
// check if the value matches any of the allowed shorthands
Iterator shorthandRefs = property.getShorthandRefs().iterator();
while (shorthandRefs.hasNext() && !isValid) {
String shorthandRef = (String) shorthandRefs.next();
Property shorthand = policy.getPropertyByName(shorthandRef);
if (shorthand != null) {
isValid = validateValue(shorthand, value);
}
}
return isValid;
}
/**
* Converts the given lexical unit to a String representation. This method does not
* perform any validation - it is meant to be used in conjunction with the validator/logging
* methods.
*
* @param lu the lexical unit to convert
* @return a String representation of the given lexical unit
*/
public String lexicalValueToString(LexicalUnit lu) {
switch (lu.getLexicalUnitType()) {
case LexicalUnit.SAC_PERCENTAGE:
case LexicalUnit.SAC_DIMENSION:
case LexicalUnit.SAC_EM:
case LexicalUnit.SAC_EX:
case LexicalUnit.SAC_PIXEL:
case LexicalUnit.SAC_INCH:
case LexicalUnit.SAC_CENTIMETER:
case LexicalUnit.SAC_MILLIMETER:
case LexicalUnit.SAC_POINT:
case LexicalUnit.SAC_PICA:
case LexicalUnit.SAC_DEGREE:
case LexicalUnit.SAC_GRADIAN:
case LexicalUnit.SAC_RADIAN:
case LexicalUnit.SAC_MILLISECOND:
case LexicalUnit.SAC_SECOND:
case LexicalUnit.SAC_HERTZ:
case LexicalUnit.SAC_KILOHERTZ:
// these are all measurements
return lu.getFloatValue() + lu.getDimensionUnitText();
case LexicalUnit.SAC_INTEGER:
// just a number
return String.valueOf(lu.getIntegerValue());
case LexicalUnit.SAC_REAL:
// just a number
return String.valueOf(lu.getFloatValue());
case LexicalUnit.SAC_STRING_VALUE:
case LexicalUnit.SAC_IDENT:
// just a string/identifier
String stringValue = lu.getStringValue();
if (stringValue.indexOf(" ") != -1) stringValue = "'" + stringValue + "'";
return stringValue;
case LexicalUnit.SAC_URI:
// this is a URL
return "url(" + lu.getStringValue() + ")";
case LexicalUnit.SAC_RGBCOLOR:
// this is a rgb encoded color
StringBuffer sb = new StringBuffer("rgb(");
LexicalUnit param = lu.getParameters();
sb.append(param.getIntegerValue()); // R value
sb.append(',');
param = param.getNextLexicalUnit(); // comma
param = param.getNextLexicalUnit(); // G value
sb.append(param.getIntegerValue());
sb.append(',');
param = param.getNextLexicalUnit(); // comma
param = param.getNextLexicalUnit(); // B value
sb.append(param.getIntegerValue());
sb.append(')');
return sb.toString();
case LexicalUnit.SAC_INHERIT:
// constant
return "inherit";
case LexicalUnit.SAC_OPERATOR_COMMA:
return ",";
case LexicalUnit.SAC_ATTR:
case LexicalUnit.SAC_COUNTER_FUNCTION:
case LexicalUnit.SAC_COUNTERS_FUNCTION:
case LexicalUnit.SAC_FUNCTION:
case LexicalUnit.SAC_RECT_FUNCTION:
case LexicalUnit.SAC_SUB_EXPRESSION:
case LexicalUnit.SAC_UNICODERANGE:
default:
// these are properties that shouldn't be necessary for most run
// of the mill HTML/CSS
return null;
}
}
}