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/*
This file is part of the iText (R) project.
Copyright (c) 1998-2024 Apryse Group NV
Authors: Apryse Software.
This program is offered under a commercial and under the AGPL license.
For commercial licensing, contact us at https://itextpdf.com/sales. For AGPL licensing, see below.
AGPL licensing:
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU Affero General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU Affero General Public License for more details.
You should have received a copy of the GNU Affero General Public License
along with this program. If not, see
* Start with one of the defaults:
*
*
* - {@link #none}
*
- {@link #simpleText}
*
- {@link #basic}
*
- {@link #basicWithImages}
*
- {@link #relaxed}
*
*
* If you need to allow more through (please be careful!), tweak a base safelist with:
*
*
* - {@link #addTags(String... tagNames)}
*
- {@link #addAttributes(String tagName, String... attributes)}
*
- {@link #addEnforcedAttribute(String tagName, String attribute, String value)}
*
- {@link #addProtocols(String tagName, String attribute, String... protocols)}
*
*
* You can remove any setting from an existing safelist with:
*
*
* - {@link #removeTags(String... tagNames)}
*
- {@link #removeAttributes(String tagName, String... attributes)}
*
- {@link #removeEnforcedAttribute(String tagName, String attribute)}
*
- {@link #removeProtocols(String tagName, String attribute, String... removeProtocols)}
*
*
*
* The cleaner and these safelists assume that you want to clean a body fragment of HTML (to add user
* supplied HTML into a templated page), and not to clean a full HTML document. If the latter is the case, either wrap the
* document HTML around the cleaned body HTML, or create a safelist that allows html and head
* elements as appropriate.
*
*
* If you are going to extend a safelist, please be very careful. Make sure you understand what attributes may lead to
* XSS attack vectors. URL attributes are particularly vulnerable and require careful validation. See
* the XSS Filter Evasion Cheat Sheet for some
* XSS attack examples (that jsoup will safegaurd against the default Cleaner and Safelist configuration).
*/
public class Safelist {
private Set tagNames; // tags allowed, lower case. e.g. [p, br, span]
private Map> attributes; // tag -> attribute[]. allowed attributes [href] for a tag.
private Map> enforcedAttributes; // always set these attribute values
private Map>> protocols; // allowed URL protocols for attributes
private boolean preserveRelativeLinks; // option to preserve relative links
/**
* This safelist allows only text nodes: all HTML will be stripped.
*
* @return safelist
*/
public static Safelist none() {
return new Safelist();
}
/**
* This safelist allows only simple text formatting: b, em, i, strong, u. All other HTML (tags and
* attributes) will be removed.
*
* @return safelist
*/
public static Safelist simpleText() {
return new Safelist()
.addTags("b", "em", "i", "strong", "u")
;
}
/**
*
* This safelist allows a fuller range of text nodes: a, b, blockquote, br, cite, code, dd, dl, dt, em, i, li,
* ol, p, pre, q, small, span, strike, strong, sub, sup, u, ul, and appropriate attributes.
*
* Links (a elements) can point to http, https, ftp, mailto, and have an enforced
* rel=nofollow attribute.
*
* Does not allow images.
*
* @return safelist
*/
public static Safelist basic() {
return new Safelist()
.addTags(
"a", "b", "blockquote", "br", "cite", "code", "dd", "dl", "dt", "em",
"i", "li", "ol", "p", "pre", "q", "small", "span", "strike", "strong", "sub",
"sup", "u", "ul")
.addAttributes("a", "href")
.addAttributes("blockquote", "cite")
.addAttributes("q", "cite")
.addProtocols("a", "href", "ftp", "http", "https", "mailto")
.addProtocols("blockquote", "cite", "http", "https")
.addProtocols("cite", "cite", "http", "https")
.addEnforcedAttribute("a", "rel", "nofollow")
;
}
/**
* This safelist allows the same text tags as {@link #basic}, and also allows img tags, with appropriate
* attributes, with src pointing to http or https.
*
* @return safelist
*/
public static Safelist basicWithImages() {
return basic()
.addTags("img")
.addAttributes("img", "align", "alt", "height", "src", "title", "width")
.addProtocols("img", "src", "http", "https")
;
}
/**
* This safelist allows a full range of text and structural body HTML: a, b, blockquote, br, caption, cite,
* code, col, colgroup, dd, div, dl, dt, em, h1, h2, h3, h4, h5, h6, i, img, li, ol, p, pre, q, small, span, strike, strong, sub,
* sup, table, tbody, td, tfoot, th, thead, tr, u, ul
*
* Links do not have an enforced rel=nofollow attribute, but you can add that if desired.
*
* @return safelist
*/
public static Safelist relaxed() {
return new Safelist()
.addTags(
"a", "b", "blockquote", "br", "caption", "cite", "code", "col",
"colgroup", "dd", "div", "dl", "dt", "em", "h1", "h2", "h3", "h4", "h5", "h6",
"i", "img", "li", "ol", "p", "pre", "q", "small", "span", "strike", "strong",
"sub", "sup", "table", "tbody", "td", "tfoot", "th", "thead", "tr", "u",
"ul")
.addAttributes("a", "href", "title")
.addAttributes("blockquote", "cite")
.addAttributes("col", "span", "width")
.addAttributes("colgroup", "span", "width")
.addAttributes("img", "align", "alt", "height", "src", "title", "width")
.addAttributes("ol", "start", "type")
.addAttributes("q", "cite")
.addAttributes("table", "summary", "width")
.addAttributes("td", "abbr", "axis", "colspan", "rowspan", "width")
.addAttributes(
"th", "abbr", "axis", "colspan", "rowspan", "scope",
"width")
.addAttributes("ul", "type")
.addProtocols("a", "href", "ftp", "http", "https", "mailto")
.addProtocols("blockquote", "cite", "http", "https")
.addProtocols("cite", "cite", "http", "https")
.addProtocols("img", "src", "http", "https")
.addProtocols("q", "cite", "http", "https")
;
}
/**
* Create a new, empty safelist. Generally it will be better to start with a default prepared safelist instead.
*
* @see #basic()
* @see #basicWithImages()
* @see #simpleText()
* @see #relaxed()
*/
public Safelist() {
tagNames = new HashSet<>();
attributes = new HashMap<>();
enforcedAttributes = new HashMap<>();
protocols = new HashMap<>();
preserveRelativeLinks = false;
}
/**
* Deep copy an existing Safelist to a new Safelist.
*
* @param copy the Safelist to copy
*/
public Safelist(Safelist copy) {
this();
tagNames.addAll(copy.tagNames);
attributes.putAll(copy.attributes);
enforcedAttributes.putAll(copy.enforcedAttributes);
protocols.putAll(copy.protocols);
preserveRelativeLinks = copy.preserveRelativeLinks;
}
/**
* Add a list of allowed elements to a safelist. (If a tag is not allowed, it will be removed from the HTML.)
*
* @param tags tag names to allow
* @return this (for chaining)
*/
public Safelist addTags(String... tags) {
Validate.notNull(tags);
for (String tagName : tags) {
Validate.notEmpty(tagName);
tagNames.add(TagName.valueOf(tagName));
}
return this;
}
/**
* Remove a list of allowed elements from a safelist. (If a tag is not allowed, it will be removed from the HTML.)
*
* @param tags tag names to disallow
* @return this (for chaining)
*/
public Safelist removeTags(String... tags) {
Validate.notNull(tags);
for (String tag : tags) {
Validate.notEmpty(tag);
TagName tagName = TagName.valueOf(tag);
if (tagNames.remove(tagName)) { // Only look in sub-maps if tag was allowed
attributes.remove(tagName);
enforcedAttributes.remove(tagName);
protocols.remove(tagName);
}
}
return this;
}
/**
* Add a list of allowed attributes to a tag. (If an attribute is not allowed on an element, it will be removed.)
*
* E.g.: addAttributes("a", "href", "class") allows href and class attributes
* on a tags.
*
* To make an attribute valid for all tags, use the pseudo tag :all, e.g.
* addAttributes(":all", "class").
*
* @param tag The tag the attributes are for. The tag will be added to the allowed tag list if necessary.
* @param attributes List of valid attributes for the tag
* @return this (for chaining)
*/
public Safelist addAttributes(String tag, String... attributes) {
Validate.notEmpty(tag);
Validate.notNull(attributes);
Validate.isTrue(attributes.length > 0, "No attribute names supplied.");
TagName tagName = TagName.valueOf(tag);
tagNames.add(tagName);
Set attributeSet = new HashSet<>();
for (String key : attributes) {
Validate.notEmpty(key);
attributeSet.add(AttributeKey.valueOf(key));
}
if (this.attributes.containsKey(tagName)) {
Set currentSet = this.attributes.get(tagName);
currentSet.addAll(attributeSet);
} else {
this.attributes.put(tagName, attributeSet);
}
return this;
}
/**
* Remove a list of allowed attributes from a tag. (If an attribute is not allowed on an element, it will be removed.)
*
* E.g.: removeAttributes("a", "href", "class") disallows href and class
* attributes on a tags.
*
* To make an attribute invalid for all tags, use the pseudo tag :all, e.g.
* removeAttributes(":all", "class").
*
* @param tag The tag the attributes are for.
* @param attributes List of invalid attributes for the tag
* @return this (for chaining)
*/
public Safelist removeAttributes(String tag, String... attributes) {
Validate.notEmpty(tag);
Validate.notNull(attributes);
Validate.isTrue(attributes.length > 0, "No attribute names supplied.");
TagName tagName = TagName.valueOf(tag);
Set attributeSet = new HashSet<>();
for (String key : attributes) {
Validate.notEmpty(key);
attributeSet.add(AttributeKey.valueOf(key));
}
if(tagNames.contains(tagName) && this.attributes.containsKey(tagName)) { // Only look in sub-maps if tag was allowed
Set currentSet = this.attributes.get(tagName);
currentSet.removeAll(attributeSet);
if(currentSet.isEmpty()) // Remove tag from attribute map if no attributes are allowed for tag
this.attributes.remove(tagName);
}
if(tag.equals(":all")) // Attribute needs to be removed from all individually set tags
for(TagName name: this.attributes.keySet()) {
Set currentSet = this.attributes.get(name);
currentSet.removeAll(attributeSet);
if(currentSet.isEmpty()) // Remove tag from attribute map if no attributes are allowed for tag
this.attributes.remove(name);
}
return this;
}
/**
* Add an enforced attribute to a tag. An enforced attribute will always be added to the element. If the element
* already has the attribute set, it will be overridden with this value.
*
* E.g.: addEnforcedAttribute("a", "rel", "nofollow") will make all a tags output as
* <a href="..." rel="nofollow">
*
* @param tag The tag the enforced attribute is for. The tag will be added to the allowed tag list if necessary.
* @param attribute The attribute name
* @param value The enforced attribute value
* @return this (for chaining)
*/
public Safelist addEnforcedAttribute(String tag, String attribute, String value) {
Validate.notEmpty(tag);
Validate.notEmpty(attribute);
Validate.notEmpty(value);
TagName tagName = TagName.valueOf(tag);
tagNames.add(tagName);
AttributeKey attrKey = AttributeKey.valueOf(attribute);
AttributeValue attrVal = AttributeValue.valueOf(value);
if (enforcedAttributes.containsKey(tagName)) {
enforcedAttributes.get(tagName).put(attrKey, attrVal);
} else {
Map attrMap = new HashMap<>();
attrMap.put(attrKey, attrVal);
enforcedAttributes.put(tagName, attrMap);
}
return this;
}
/**
* Remove a previously configured enforced attribute from a tag.
*
* @param tag The tag the enforced attribute is for.
* @param attribute The attribute name
* @return this (for chaining)
*/
public Safelist removeEnforcedAttribute(String tag, String attribute) {
Validate.notEmpty(tag);
Validate.notEmpty(attribute);
TagName tagName = TagName.valueOf(tag);
if(tagNames.contains(tagName) && enforcedAttributes.containsKey(tagName)) {
AttributeKey attrKey = AttributeKey.valueOf(attribute);
Map attrMap = enforcedAttributes.get(tagName);
attrMap.remove(attrKey);
if(attrMap.isEmpty()) // Remove tag from enforced attribute map if no enforced attributes are present
enforcedAttributes.remove(tagName);
}
return this;
}
/**
* Configure this Safelist to preserve relative links in an element's URL attribute, or convert them to absolute
* links. By default, this is false: URLs will be made absolute (e.g. start with an allowed protocol, like
* e.g. {@code http://}.
*
* Note that when handling relative links, the input document must have an appropriate {@code base URI} set when
* parsing, so that the link's protocol can be confirmed. Regardless of the setting of the {@code preserve relative
* links} option, the link must be resolvable against the base URI to an allowed protocol; otherwise the attribute
* will be removed.
*
* @param preserve {@code true} to allow relative links, {@code false} (default) to deny
* @return this Safelist, for chaining.
* @see #addProtocols
*/
public Safelist preserveRelativeLinks(boolean preserve) {
preserveRelativeLinks = preserve;
return this;
}
/**
* Add allowed URL protocols for an element's URL attribute. This restricts the possible values of the attribute to
* URLs with the defined protocol.
*
* E.g.: addProtocols("a", "href", "ftp", "http", "https")
*
* To allow a link to an in-page URL anchor (i.e. <a href="#anchor">, add a #:
* E.g.: addProtocols("a", "href", "#")
*
* @param tag Tag the URL protocol is for
* @param attribute Attribute name
* @param protocols List of valid protocols
* @return this, for chaining
*/
public Safelist addProtocols(String tag, String attribute, String... protocols) {
Validate.notEmpty(tag);
Validate.notEmpty(attribute);
Validate.notNull(protocols);
TagName tagName = TagName.valueOf(tag);
AttributeKey attrKey = AttributeKey.valueOf(attribute);
Map> attrMap;
Set protSet;
if (this.protocols.containsKey(tagName)) {
attrMap = this.protocols.get(tagName);
} else {
attrMap = new HashMap<>();
this.protocols.put(tagName, attrMap);
}
if (attrMap.containsKey(attrKey)) {
protSet = attrMap.get(attrKey);
} else {
protSet = new HashSet<>();
attrMap.put(attrKey, protSet);
}
for (String protocol : protocols) {
Validate.notEmpty(protocol);
Protocol prot = Protocol.valueOf(protocol);
protSet.add(prot);
}
return this;
}
/**
* Remove allowed URL protocols for an element's URL attribute. If you remove all protocols for an attribute, that
* attribute will allow any protocol.
*
* E.g.: removeProtocols("a", "href", "ftp")
*
* @param tag Tag the URL protocol is for
* @param attribute Attribute name
* @param removeProtocols List of invalid protocols
* @return this, for chaining
*/
public Safelist removeProtocols(String tag, String attribute, String... removeProtocols) {
Validate.notEmpty(tag);
Validate.notEmpty(attribute);
Validate.notNull(removeProtocols);
TagName tagName = TagName.valueOf(tag);
AttributeKey attr = AttributeKey.valueOf(attribute);
// make sure that what we're removing actually exists; otherwise can open the tag to any data and that can
// be surprising
Validate.isTrue(protocols.containsKey(tagName), "Cannot remove a protocol that is not set.");
Map> tagProtocols = protocols.get(tagName);
Validate.isTrue(tagProtocols.containsKey(attr), "Cannot remove a protocol that is not set.");
Set attrProtocols = tagProtocols.get(attr);
for (String protocol : removeProtocols) {
Validate.notEmpty(protocol);
attrProtocols.remove(Protocol.valueOf(protocol));
}
if (attrProtocols.isEmpty()) { // Remove protocol set if empty
tagProtocols.remove(attr);
if (tagProtocols.isEmpty()) // Remove entry for tag if empty
protocols.remove(tagName);
}
return this;
}
/**
* Test if the supplied tag is allowed by this safelist
*
* @param tag test tag
* @return true if allowed
*/
protected boolean isSafeTag(String tag) {
return tagNames.contains(TagName.valueOf(tag));
}
/**
* Test if the supplied attribute is allowed by this safelist for this tag
*
* @param tagName tag to consider allowing the attribute in
* @param el element under test, to confirm protocol
* @param attr attribute under test
* @return true if allowed
*/
protected boolean isSafeAttribute(String tagName, Element el, Attribute attr) {
TagName tag = TagName.valueOf(tagName);
AttributeKey key = AttributeKey.valueOf(attr.getKey());
Set okSet = attributes.get(tag);
if (okSet != null && okSet.contains(key)) {
if (protocols.containsKey(tag)) {
Map> attrProts = protocols.get(tag);
// ok if not defined protocol; otherwise test
return !attrProts.containsKey(key) || testValidProtocol(el, attr, attrProts.get(key));
} else { // attribute found, no protocols defined, so OK
return true;
}
}
// might be an enforced attribute?
Map enforcedSet = enforcedAttributes.get(tag);
if (enforcedSet != null) {
Attributes expect = getEnforcedAttributes(tagName);
String attrKey = attr.getKey();
if (expect.hasKeyIgnoreCase(attrKey)) {
return expect.getIgnoreCase(attrKey).equals(attr.getValue());
}
}
// no attributes defined for tag, try :all tag
return !tagName.equals(":all") && isSafeAttribute(":all", el, attr);
}
private boolean testValidProtocol(Element el, Attribute attr, Set protocols) {
// try to resolve relative urls to abs, and optionally update the attribute so output html has abs.
// rels without a baseuri get removed
String value = el.absUrl(attr.getKey());
if (value.length() == 0)
value = attr.getValue(); // if it could not be made abs, run as-is to allow custom unknown protocols
if (!preserveRelativeLinks)
attr.setValue(value);
for (Protocol protocol : protocols) {
String prot = protocol.toString();
if (prot.equals("#")) { // allows anchor links
if (isValidAnchor(value)) {
return true;
} else {
continue;
}
}
prot += ":";
if (Normalizer.lowerCase(value).startsWith(prot)) {
return true;
}
}
return false;
}
private boolean isValidAnchor(String value) {
return value.startsWith("#") && !value.matches(".*\\s.*");
}
Attributes getEnforcedAttributes(String tagName) {
Attributes attrs = new Attributes();
TagName tag = TagName.valueOf(tagName);
if (enforcedAttributes.containsKey(tag)) {
Map keyVals = enforcedAttributes.get(tag);
for (Map.Entry entry : keyVals.entrySet()) {
attrs.put(entry.getKey().toString(), entry.getValue().toString());
}
}
return attrs;
}
// named types for config. All just hold strings, but here for my sanity.
static class TagName extends TypedValue {
TagName(String value) {
super(value);
}
static TagName valueOf(String value) {
return new TagName(value);
}
}
static class AttributeKey extends TypedValue {
AttributeKey(String value) {
super(value);
}
static AttributeKey valueOf(String value) {
return new AttributeKey(value);
}
}
static class AttributeValue extends TypedValue {
AttributeValue(String value) {
super(value);
}
static AttributeValue valueOf(String value) {
return new AttributeValue(value);
}
}
static class Protocol extends TypedValue {
Protocol(String value) {
super(value);
}
static Protocol valueOf(String value) {
return new Protocol(value);
}
}
abstract static class TypedValue {
private String value;
TypedValue(String value) {
Validate.notNull(value);
this.value = value;
}
@Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + ((value == null) ? 0 : value.hashCode());
return result;
}
@Override
public boolean equals(Object obj) {
if (this == obj) return true;
if (obj == null) return false;
if (getClass() != obj.getClass()) return false;
TypedValue other = (TypedValue) obj;
if (value == null) {
return other.value == null;
} else return value.equals(other.value);
}
@Override
public String toString() {
return value;
}
}
}