{
    "CVE_data_meta": {
        "ASSIGNER": "security@apache.org",
        "ID": "CVE-2021-27850",
        "STATE": "PUBLIC",
        "TITLE": "Bypass of the fix for CVE-2019-0195"
    },
    "affects": {
        "vendor": {
            "vendor_data": [
                {
                    "product": {
                        "product_data": [
                            {
                                "product_name": "Apache Tapestry",
                                "version": {
                                    "version_data": [
                                        {
                                            "version_affected": ">=",
                                            "version_name": "Apache Tapestry 5.4.0",
                                            "version_value": "Apache Tapestry 5.4.5"
                                        },
                                        {
                                            "version_affected": "=",
                                            "version_name": "Apache Tapestry 5.5.0",
                                            "version_value": "Apache Tapestry 5.5.0"
                                        },
                                        {
                                            "version_affected": ">=",
                                            "version_name": "Apache Tapestry 5.6.0",
                                            "version_value": "Apache Tapestry 5.6.2"
                                        },
                                        {
                                            "version_affected": "=",
                                            "version_name": "Apache Tapestry 5.7.0",
                                            "version_value": "Apache Tapestry 5.7.0"
                                        }
                                    ]
                                }
                            }
                        ]
                    },
                    "vendor_name": "Apache Software Foundation"
                }
            ]
        }
    },
    "credit": [
        {
            "lang": "eng",
            "value": "Apache Tapestry would like to thank Johannes Moritz for finding and notifying this vulnerability"
        }
    ],
    "data_format": "MITRE",
    "data_type": "CVE",
    "data_version": "4.0",
    "description": {
        "description_data": [
            {
                "lang": "eng",
                "value": "A critical unauthenticated remote code execution vulnerability was found all recent versions of Apache Tapestry. The affected versions include 5.4.5, 5.5.0, 5.6.2 and 5.7.0. The vulnerability I have found is a bypass of the fix for CVE-2019-0195. Recap: Before the fix of CVE-2019-0195 it was possible to download arbitrary class files from the classpath by providing a crafted asset file URL. An attacker was able to download the file `AppModule.class` by requesting the URL `http://localhost:8080/assets/something/services/AppModule.class` which contains a HMAC secret key. The fix for that bug was a blacklist filter that checks if the URL ends with `.class`, `.properties` or `.xml`. Bypass: Unfortunately, the blacklist solution can simply be bypassed by appending a `/` at the end of the URL: `http://localhost:8080/assets/something/services/AppModule.class/` The slash is stripped after the blacklist check and the file `AppModule.class` is loaded into the response. This class usually contains the HMAC secret key which is used to sign serialized Java objects. With the knowledge of that key an attacker can sign a Java gadget chain that leads to RCE (e.g. CommonsBeanUtils1 from ysoserial). Solution for this vulnerability: * For Apache Tapestry 5.4.0 to 5.6.1, upgrade to 5.6.2 or later. * For Apache Tapestry 5.7.0, upgrade to 5.7.1 or later."
            }
        ]
    },
    "generator": {
        "engine": "Vulnogram 0.0.9"
    },
    "problemtype": {
        "problemtype_data": [
            {
                "description": [
                    {
                        "lang": "eng",
                        "value": "CWE-200 Information Exposure"
                    }
                ]
            },
            {
                "description": [
                    {
                        "lang": "eng",
                        "value": "CWE-502 Deserialization of Untrusted Data"
                    }
                ]
            }
        ]
    },
    "references": {
        "reference_data": [
            {
                "refsource": "MISC",
                "url": "https://lists.apache.org/thread.html/r237ff7f286bda31682c254550c1ebf92b0ec61329b32fbeb2d1c8751%40%3Cusers.tapestry.apache.org%3E",
                "name": "https://lists.apache.org/thread.html/r237ff7f286bda31682c254550c1ebf92b0ec61329b32fbeb2d1c8751%40%3Cusers.tapestry.apache.org%3E"
            },
            {
                "refsource": "MLIST",
                "name": "[oss-security] 20210414 CVE-2021-27850: Apache Tapestry: Bypass of the fix for CVE-2019-0195",
                "url": "http://www.openwall.com/lists/oss-security/2021/04/15/1"
            },
            {
                "refsource": "CONFIRM",
                "name": "https://security.netapp.com/advisory/ntap-20210528-0002/",
                "url": "https://security.netapp.com/advisory/ntap-20210528-0002/"
            }
        ]
    },
    "source": {
        "defect": [
            "TAP5-2663"
        ],
        "discovery": "UNKNOWN"
    }
}