{"id":"CVE-2021-27850","aliases":["EUVD-2021-1359","GHSA-mj8x-cpr8-x39h"],"status":"published","title":"Bypass of the fix for CVE-2019-0195","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.","severity":{"version":"3.1","score":9.8,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","level":"critical","assessor":"primary","from":"nvd"},"epss":{"day":"2026-11-12","score":0.9356,"percentile":0.99843,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":true,"fix_available":true},"cwes":["CWE-200","CWE-502","CWE-922"],"published":"2021-04-15T07:40:11Z","modified":"2026-10-25T01:16:50Z","exploits":[{"source":"metasploit","id":"auxiliary/gather/cve_2021_27850_apache_tapestry_hmac_key","title":"Apache Tapestry HMAC secret key leak","type":"auxiliary","date":"2021-04-15","verified":true,"url":"https://www.rapid7.com/db/modules/auxiliary/gather/cve_2021_27850_apache_tapestry_hmac_key"},{"source":"nuclei","id":"CVE-2021-27850","title":"Apache Tapestry - Remote Code Execution","type":"detection template","url":"https://github.com/projectdiscovery/nuclei-templates/blob/main/http/cves/2021/CVE-2021-27850.yaml"},{"source":"pocgithub","id":"Ovi3/CVE_2021_27850_POC","title":"Ovi3/CVE_2021_27850_POC","date":"2021-07-02","url":"https://github.com/Ovi3/CVE_2021_27850_POC"},{"source":"pocgithub","id":"dorkerdevil/CVE-2021-27850_POC","title":"dorkerdevil/CVE-2021-27850_POC","date":"2021-06-26","url":"https://github.com/dorkerdevil/CVE-2021-27850_POC"},{"source":"pocgithub","id":"kahla-sec/CVE-2021-27850_POC","title":"kahla-sec/CVE-2021-27850_POC","date":"2021-06-25","url":"https://github.com/kahla-sec/CVE-2021-27850_POC"},{"source":"pocgithub","id":"novysodope/CVE-2021-27850","title":"novysodope/CVE-2021-27850","date":"2022-07-07","url":"https://github.com/novysodope/CVE-2021-27850"}],"fixes":[{"ecosystem":"Maven","package":"org.apache.tapestry:tapestry-core","fixed_in":["5.6.3","5.7.1"],"sources":["ghsa","osv"]}],"affected":[{"source":"ghsa","ecosystem":"Maven","package":"org.apache.tapestry:tapestry-core","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"5.4.0"},{"fixed":"5.6.3"}]}]},{"source":"ghsa","ecosystem":"Maven","package":"org.apache.tapestry:tapestry-core","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"5.7.0"},{"fixed":"5.7.1"}]}]},{"source":"osv","ecosystem":"Maven","package":"org.apache.tapestry:tapestry-core","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"5.4.0"},{"fixed":"5.6.3"}]}],"versions":["5.4.0","5.4.1","5.4.2","5.4.3","5.4.4","5.4.5","5.5.0","5.5.0-beta-3","5.6.0","5.6.1","5.6.2"]},{"source":"osv","ecosystem":"Maven","package":"org.apache.tapestry:tapestry-core","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"5.7.0"},{"fixed":"5.7.1"}]}],"versions":["5.7.0"]}],"products":[{"vendor":"apache","product":"tapestry"},{"vendor":"apache software foundation","product":"apache tapestry"}],"references":[{"url":"https://lists.apache.org/thread.html/r237ff7f286bda31682c254550c1ebf92b0ec61329b32fbeb2d1c8751%40%3Cusers.tapestry.apache.org%3E","tags":["x_refsource_MISC","x_transferred","Mailing List","Vendor Advisory","advisory","web"]},{"url":"http://www.openwall.com/lists/oss-security/2021/04/15/1","tags":["mailing-list","x_refsource_MLIST","x_transferred","Exploit","Mailing List","Third Party Advisory","evidence","web"]},{"url":"https://security.netapp.com/advisory/ntap-20210528-0002/","tags":["x_refsource_CONFIRM","x_transferred","Third Party Advisory","advisory"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2021-27850","tags":["advisory"]},{"url":"https://issues.apache.org/jira/browse/TAP5-2663","tags":["web"]},{"url":"https://github.com/advisories/GHSA-mj8x-cpr8-x39h"},{"url":"https://security.netapp.com/advisory/ntap-20210528-0002","tags":["web"]}],"sources":{"cve":[{"id":"CVE-2021-27850","title":"Bypass of the fix for CVE-2019-0195","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.","status":"published","published":"2021-04-15T07:40:11Z","modified":"2024-08-03T21:33:15.996Z","cwes":["CWE-200","CWE-502"],"updated_at":"2026-11-02T14:33:04.360272Z"}],"euvd":[{"id":"EUVD-2021-1359","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.","status":"published","published":"2021-04-15T07:40:11Z","modified":"2024-08-03T21:33:15Z","updated_at":"2026-11-03T03:24:48.366655Z"}],"ghsa":[{"id":"GHSA-mj8x-cpr8-x39h","title":"Remote code execution in Apache Tapestry","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 5.6.2, upgrade to 5.6.3 or later. * For Apache Tapestry 5.7.0, upgrade to 5.7.1 or later.","status":"published","published":"2021-06-16T17:33:19Z","modified":"2023-02-01T05:05:28Z","cwes":["CWE-502","CWE-922"],"updated_at":"2026-11-02T14:36:34.260786Z"}],"nvd":[{"id":"CVE-2021-27850","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.","status":"published","published":"2021-04-15T08:15:14.823Z","modified":"2026-06-17T03:45:30.777Z","cvss":[{"version":"3.1","score":9.8,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","level":"critical","assessor":"primary"},{"version":"2.0","score":10,"vector":"AV:N/AC:L/Au:N/C:C/I:C/A:C","level":"high","assessor":"primary"}],"cwes":["CWE-200","CWE-502"],"updated_at":"2026-11-02T14:06:52.03307Z"}],"osv":[{"id":"CVE-2021-27850","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.","status":"published","published":"2021-04-15T08:15:14.823Z","modified":"2026-10-25T01:16:50.374558639Z","cvss":[{"version":"3.1","score":9.8,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","level":"critical"}],"updated_at":"2026-11-02T15:44:19.129331Z"},{"id":"GHSA-mj8x-cpr8-x39h","title":"Remote code execution in Apache Tapestry","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 5.6.2, upgrade to 5.6.3 or later. * For Apache Tapestry 5.7.0, upgrade to 5.7.1 or later.","status":"published","published":"2021-06-16T17:33:19Z","modified":"2024-12-02T05:47:35.826691Z","cwes":["CWE-502","CWE-922"],"updated_at":"2026-11-02T15:46:51.811331Z"}]}}