CVE-2021-27850
A critical unauthenticated remote code execution vulnerability was found all recent versions of Apache Tapestry.
Does this matter?
EPSS puts the probability of exploitation in the next 30 days at 93.5%, higher than 100% of all known CVEs. Patch or mitigate before the next change window.
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.
- CVSS 3.1
- 9.8 CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- EPSS
- 93.47% probability · 100th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-200, CWE-502
- Affected
- apache/tapestry
- Source
- security@apache.org
References
- http://www.openwall.com/lists/oss-security/2021/04/15/1Exploit, Mailing List, Third Party Advisory
- https://lists.apache.org/thread.html/r237ff7f286bda31682c254550c1ebf92b0ec61329b32fbeb2d1c8751%40%3Cusers.tapestry.apache.org%3EMailing List, Vendor Advisory
- https://security.netapp.com/advisory/ntap-20210528-0002/Third Party Advisory
- http://www.openwall.com/lists/oss-security/2021/04/15/1Exploit, Mailing List, Third Party Advisory
- https://lists.apache.org/thread.html/r237ff7f286bda31682c254550c1ebf92b0ec61329b32fbeb2d1c8751%40%3Cusers.tapestry.apache.org%3EMailing List, Vendor Advisory
- https://security.netapp.com/advisory/ntap-20210528-0002/Third Party Advisory
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.