{
  "affected": [
    {
      "ranges": [
        {
          "database_specific": {
            "cpe": "cpe:2.3:a:apache:tapestry:*:*:*:*:*:*:*:*",
            "extracted_events": [
              {
                "introduced": "5.4.0"
              },
              {
                "fixed": "5.6.2"
              },
              {
                "introduced": "5.7.0"
              },
              {
                "fixed": "5.7.1"
              }
            ],
            "source": "CPE_RANGE"
          },
          "events": [
            {
              "introduced": "2672e9847ad56d2b3f83c28319b532b92d6af5c9"
            },
            {
              "fixed": "6f631e9abf8cc08bd269e6aaa1e2f02f5fdf99df"
            },
            {
              "introduced": "e6f2930cddbd22cae01629be1f615cf2d6fae53b"
            },
            {
              "fixed": "ce9c2e8e49669a7d7e68c347f1d95e79ece74ae4"
            }
          ],
          "repo": "https://github.com/apache/tapestry-5",
          "type": "GIT"
        }
      ]
    }
  ],
  "database_specific": {},
  "details": "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.",
  "id": "CVE-2021-27850",
  "modified": "2026-07-08T05:36:19.447708155Z",
  "published": "2021-04-15T08:15:14.823Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://lists.apache.org/thread.html/r237ff7f286bda31682c254550c1ebf92b0ec61329b32fbeb2d1c8751%40%3Cusers.tapestry.apache.org%3E"
    },
    {
      "type": "ADVISORY",
      "url": "https://security.netapp.com/advisory/ntap-20210528-0002/"
    },
    {
      "type": "EVIDENCE",
      "url": "http://www.openwall.com/lists/oss-security/2021/04/15/1"
    }
  ],
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ]
}