Spring Cloud Gateway网关XSS过滤

XSS是一种经常出现在web应用中的计算机安全漏洞，具体信息请自行Google。本文只分享在Spring Cloud Gateway中执行通用的XSS防范。首次作文，全是代码，若有遗漏不明之处，请各位看官原谅指点。

使用版本

Spring Cloud版本为 Greenwich.SR4
Spring Boot版本为 2.1.11.RELEASE

1.创建一个Filter。

特别注意的是在处理完成之后需要重新构造请求，否则后续业务无法获得参数。

import io.netty.buffer.ByteBufAllocator;
import lombok.AllArgsConstructor;
import lombok.Builder;
import lombok.Data;
import lombok.NoArgsConstructor;
import lombok.extern.slf4j.Slf4j;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.cloud.gateway.filter.GatewayFilterChain;
import org.springframework.cloud.gateway.filter.GlobalFilter;
import org.springframework.core.Ordered;
import org.springframework.core.io.buffer.DataBuffer;
import org.springframework.core.io.buffer.DataBufferUtils;
import org.springframework.core.io.buffer.NettyDataBufferFactory;
import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpMethod;
import org.springframework.http.server.reactive.ServerHttpRequest;
import org.springframework.http.server.reactive.ServerHttpRequestDecorator;
import org.springframework.stereotype.Component;
import org.springframework.util.Assert;
import org.springframework.util.DigestUtils;
import org.springframework.validation.annotation.Validated;
import org.springframework.web.server.ServerWebExchange;
import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;

import javax.validation.constraints.NotEmpty;
import java.net.URI;
import java.nio.charset.StandardCharsets;
import java.util.List;
import java.util.Optional;

/**
 * XSS过滤
 *
 * @author lieber
 */
@Component
@Slf4j
@ConfigurationProperties("config.xss")
@Data
public class XssFilter implements GlobalFilter, Ordered {

    private List<XssWhiteUrl> whiteUrls;

    @Override
    public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
        ServerHttpRequest request = exchange.getRequest();
        URI uri = request.getURI();
        String method = request.getMethodValue();
        // 判断是否在白名单中
        if (this.white(uri.getPath(), method)) {
            return chain.filter(exchange);
        }
        // 只拦截POST和PUT请求
        if ((HttpMethod.POST.name().equals(method) || HttpMethod.PUT.name().equals(method))) {
            return DataBufferUtils.join(request.getBody())
                    .flatMap(dataBuffer -> {
                        // 取出body中的参数
                        byte[] oldBytes = new byte[dataBuffer.readableByteCount()];
                        dataBuffer.read(oldBytes);
                        String bodyString = new String(oldBytes, StandardCharsets.UTF_8);
                        log.debug("原请求参数为：{}", bodyString);
                        // 执行XSS清理
                        bodyString = XssUtil.INSTANCE.cleanXss(bodyString);
                        log.debug("修改后参数为：{}", bodyString);

                        ServerHttpRequest newRequest = request.mutate().uri(uri).build();

                        // 重新构造body
                        byte[] newBytes = bodyString.getBytes(StandardCharsets.UTF_8);
                        DataBuffer bodyDataBuffer = toDataBuffer(newBytes);
                        Flux<DataBuffer> bodyFlux = Flux.just(bodyDataBuffer);

                        // 重新构造header
                        HttpHeaders headers = new HttpHeaders();
                        headers.putAll(request.getHeaders());
                        // 由于修改了传递参数，需要重新设置CONTENT_LENGTH，长度是字节长度，不是字符串长度
                        int length = newBytes.length;
                        headers.remove(HttpHeaders.CONTENT_LENGTH);
                        headers.setContentLength(length);
                        headers.set(HttpHeaders.CONTENT_TYPE, "application/json;charset=utf8");
                        // 重写ServerHttpRequestDecorator，修改了body和header，重写getBody和getHeaders方法
                        newRequest = new ServerHttpRequestDecorator(newRequest) {
                            @Override
                            public Flux<DataBuffer> getBody() {
                                return bodyFlux;
                            }

                            @Override
                            public HttpHeaders getHeaders() {
                                return headers;
                            }
                        };

                        return chain.filter(exchange.mutate().request(newRequest).build());
                    });
        } else {
            return chain.filter(exchange);
        }
    }

    /**
     * 是否是白名单
     *
     * @param url    路由
     * @param method 请求方式
     * @return true/false
     */
    private boolean white(String url, String method) {
        return whiteUrls != null && whiteUrls.contains(XssWhiteUrl.builder().url(url).method(method).build());
    }

    /**
     * 字节数组转DataBuffer
     *
     * @param bytes 字节数组
     * @return DataBuffer
     */
    private DataBuffer toDataBuffer(byte[] bytes) {
        NettyDataBufferFactory nettyDataBufferFactory = new NettyDataBufferFactory(ByteBufAllocator.DEFAULT);
        DataBuffer buffer = nettyDataBufferFactory.allocateBuffer(bytes.length);
        buffer.write(bytes);
        return buffer;
    }

    public static final int ORDER = 10;

    @Override
    public int getOrder() {
        return ORDER;
    }

    @Data
    @Validated
    @AllArgsConstructor
    @NoArgsConstructor
    private static class XssWhiteUrl {

        @NotEmpty
        private String url;

        @NotEmpty
        private String method;
    }
}

2. 处理XSS字符串。

这里大范围采用Jsoup处理，然后根据自己的业务做了一部分定制。较为特殊的是，我们将字符串中含有'</'标示为这段文本是富文本。在清除xss攻击字符串方法时优化空间较大。

import com.alibaba.fastjson.JSONObject;
import org.jsoup.Jsoup;
import org.jsoup.nodes.Document;
import org.jsoup.safety.Whitelist;

import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.Objects;

/**
 * xss拦截工具类
 *
 * @author lieber
 */
public enum XssUtil {

    /**
     * 实例
     */
    INSTANCE;

    private final static String RICH_TEXT = "</";

    /**
     * 自定义白名单
     */
    private final static Whitelist CUSTOM_WHITELIST = Whitelist.relaxed()
            .addAttributes("video", "width", "height", "controls", "alt", "src")
            .addAttributes(":all", "style", "class");

    /**
     * jsoup不格式化代码
     */
    private final static Document.OutputSettings OUTPUT_SETTINGS = new Document.OutputSettings().prettyPrint(false);

    /**
     * 清除json对象中的xss攻击字符
     *
     * @param val json对象字符串
     * @return 清除后的json对象字符串
     */
    private String cleanObj(String val) {
        JSONObject jsonObject = JSONObject.parseObject(val);
        for (Map.Entry<String, Object> entry : jsonObject.entrySet()) {
            if (entry.getValue() != null && entry.getValue() instanceof String) {
                String str = (String) entry.getValue();
                str = this.cleanXss(str);
                entry.setValue(str);
            }
        }
        return jsonObject.toJSONString();
    }

    /**
     * 清除json数组中的xss攻击字符
     *
     * @param val json数组字符串
     * @return 清除后的json数组字符串
     */
    private String cleanArr(String val) {
        List<String> list = JSONObject.parseArray(val, String.class);
        List<String> result = new ArrayList<>(list.size());
        for (String str : list) {
            str = this.cleanXss(str);
            result.add(str);
        }
        return JSONObject.toJSONString(result);
    }

    /**
     * 清除xss攻击字符串，此处优化空间较大
     *
     * @param str 字符串
     * @return 清除后无害的字符串
     */
    public String cleanXss(String str) {
        if (JsonUtil.INSTANCE.isJsonObj(str)) {
            str = this.cleanObj(str);
        } else if (JsonUtil.INSTANCE.isJsonArr(str)) {
            str = this.cleanArr(str);
        } else {
            boolean richText = this.richText(str);
            if (!richText) {
                str = str.trim();
                str = str.replaceAll(" +", " ");
            }
            String afterClean = Jsoup.clean(str, "", CUSTOM_WHITELIST, OUTPUT_SETTINGS);
            if (paramError(richText, afterClean, str)) {
                throw new BizRunTimeException(ApiCode.PARAM_ERROR, "参数包含特殊字符");
            }
            str = richText ? afterClean : this.backSpecialStr(afterClean);
        }
        return str;
    }


    /**
     * 判断是否是富文本
     *
     * @param str 待判断字符串
     * @return true/false
     */
    private boolean richText(String str) {
        return str.contains(RICH_TEXT);
    }

    /**
     * 判断是否参数错误
     *
     * @param richText   是否富文本
     * @param afterClean 清理后字符
     * @param str        原字符串
     * @return true/false
     */
    private boolean paramError(boolean richText, String afterClean, String str) {
        // 如果包含富文本字符，那么不是参数错误
        if (richText) {
            return false;
        }
        // 如果清理后的字符和清理前的字符匹配，那么不是参数错误
        if (Objects.equals(str, afterClean)) {
            return false;
        }
        // 如果仅仅包含可以通过的特殊字符，那么不是参数错误
        if (Objects.equals(str, this.backSpecialStr(afterClean))) {
            return false;
        }
        // 如果还有......
        return true;
    }

    /**
     * 转义回特殊字符
     *
     * @param str 已经通过转义字符
     * @return 转义后特殊字符
     */
    private String backSpecialStr(String str) {
        return str.replaceAll("&amp;", "&");
    }
}

3.其它使用到的工具


import com.alibaba.fastjson.JSONObject;
import org.springframework.util.StringUtils;

/**
 * JSON处理工具类
 *
 * @author lieber
 */
public enum JsonUtil {

    /**
     * 实例
     */
    INSTANCE;

    /**
     * json对象字符串开始标记
     */
    private final static String JSON_OBJECT_START = "{";

    /**
     * json对象字符串结束标记
     */
    private final static String JSON_OBJECT_END = "}";

    /**
     * json数组字符串开始标记
     */
    private final static String JSON_ARRAY_START = "[";

    /**
     * json数组字符串结束标记
     */
    private final static String JSON_ARRAY_END = "]";


    /**
     * 判断字符串是否json对象字符串
     *
     * @param val 字符串
     * @return true/false
     */
    public boolean isJsonObj(String val) {
        if (StringUtils.isEmpty(val)) {
            return false;
        }
        val = val.trim();
        if (val.startsWith(JSON_OBJECT_START) && val.endsWith(JSON_OBJECT_END)) {
            try {
                JSONObject.parseObject(val);
                return true;
            } catch (Exception e) {
                return false;
            }
        }
        return false;
    }

    /**
     * 判断字符串是否json数组字符串
     *
     * @param val 字符串
     * @return true/false
     */
    public boolean isJsonArr(String val) {
        if (StringUtils.isEmpty(val)) {
            return false;
        }
        val = val.trim();
        if (StringUtils.isEmpty(val)) {
            return false;
        }
        val = val.trim();
        if (val.startsWith(JSON_ARRAY_START) && val.endsWith(JSON_ARRAY_END)) {
            try {
                JSONObject.parseArray(val);
                return true;
            } catch (Exception e) {
                return false;
            }
        }
        return false;
    }

    /**
     * 判断对象是否是json对象
     *
     * @param obj 待判断对象
     * @return true/false
     */
    public boolean isJsonObj(Object obj) {
        String str = JSONObject.toJSONString(obj);
        return this.isJsonObj(str);
    }

    /**
     * 判断字符串是否json字符串
     *
     * @param str 字符串
     * @return true/false
     */
    public boolean isJson(String str) {
        if (StringUtils.isEmpty(str)) {
            return false;
        }
        return this.isJsonObj(str) || this.isJsonArr(str);
    }
}

大功告成。

------------------------------------------手动分隔--------------------------------------------------------------

修改

在第一步创建Filter时有问题，原因是使用了新旧代码的问题，现已经将元代码放在正文，新代码如下

@Override
    public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
        ServerHttpRequest request = exchange.getRequest();
        URI uri = request.getURI();
        String method = request.getMethodValue();
        if (this.white(uri.getPath(), method)) {
            return chain.filter(exchange);
        }
        if ((HttpMethod.POST.name().equals(method) || HttpMethod.PUT.name().equals(method))) {
            return DataBufferUtils.join(request.getBody()).flatMap(d -> Mono.just(Optional.of(d))).defaultIfEmpty(Optional.empty())
                    .flatMap(optional -> {
                        // 取出body中的参数
                        String bodyString = "";
                        if (optional.isPresent()) {
                            byte[] oldBytes = new byte[optional.get().readableByteCount()];
                            optional.get().read(oldBytes);
                            bodyString = new String(oldBytes, StandardCharsets.UTF_8);
                        }
                        HttpHeaders httpHeaders = request.getHeaders();
                        // 执行XSS清理
                        log.debug("{} - [{}：{}] XSS处理前参数：{}", method, uri.getPath(), bodyString);
                        bodyString = XssUtil.INSTANCE.cleanXss(bodyString);
                        log.info("{} - [{}：{}] 参数：{}", method, uri.getPath(), bodyString);
                        
                        ServerHttpRequest newRequest = request.mutate().uri(uri).build();

                        // 重新构造body
                        byte[] newBytes = bodyString.getBytes(StandardCharsets.UTF_8);
                        DataBuffer bodyDataBuffer = toDataBuffer(newBytes);
                        Flux<DataBuffer> bodyFlux = Flux.just(bodyDataBuffer);

                        // 重新构造header
                        HttpHeaders headers = new HttpHeaders();
                        headers.putAll(httpHeaders);
                        // 由于修改了传递参数，需要重新设置CONTENT_LENGTH，长度是字节长度，不是字符串长度
                        int length = newBytes.length;
                        headers.remove(HttpHeaders.CONTENT_LENGTH);
                        headers.setContentLength(length);
                        headers.set(HttpHeaders.CONTENT_TYPE, "application/json;charset=utf8");
                        // 重写ServerHttpRequestDecorator，修改了body和header，重写getBody和getHeaders方法
                        newRequest = new ServerHttpRequestDecorator(newRequest) {
                            @Override
                            public Flux<DataBuffer> getBody() {
                                return bodyFlux;
                            }

                            @Override
                            public HttpHeaders getHeaders() {
                                return headers;
                            }
                        };

                        return chain.filter(exchange.mutate().request(newRequest).build());
                    });
        } else {
            return chain.filter(exchange);
        }
    }