cve-2021-27850

{
  "cvss": 0.0,
  "datePublished": "2023-12-03T00:00:00Z",
  "dateUpdated": "2023-12-03T00:00:00Z",
  "description": "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.",
  "dueDate": "",
  "id": "CVE-2021-27850",
  "kev_catalogs": [
    "vulncheck"
  ],
  "knownRansomwareCampaignUse": "Unknown",
  "product": "tapestry",
  "requiredAction": "Apply remediations or mitigations per vendor instructions or discontinue use of the product if remediation or mitigations are unavailable.",
  "severity": "HIGH",
  "source": "vulncheck_kev",
  "title": "Apache tapestry Exposure of Sensitive Information to an Unauthorized Actor",
  "vendor": "Apache"
}