This High severity Third-Party Dependency vulnerability was introduced in versions 8.19.0, 9.4.0, and 9.6.0 of Bitbucket Data Center and Server.

This Third-Party Dependency vulnerability, with a CVSS Score of 7.5 and a CVSS Vector of CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N allows an unauthenticated attacker to expose assets in your environment susceptible to exploitation which has high impact to confidentiality, no impact to integrity, no impact to availability, and requires no user interaction.

Atlassian recommends that Bitbucket Data Center and Server customers upgrade to latest version, if you are unable to do so, upgrade your instance to one of the specified supported fixed versions:

• Bitbucket Data Center and Server 8.19: Upgrade to a release greater than or equal to 8.19.21

• Bitbucket Data Center and Server 9.4: Upgrade to a release greater than or equal to 9.4.9

• Bitbucket Data Center and Server 9.6: Upgrade to a release greater than or equal to 9.6.5

See the release notes (https://confluence.atlassian.com/bitbucketserver/release-notes). You can download the latest version of Bitbucket Data Center and Server from the download center (https://www.atlassian.com/software/bitbucket/download-archives).

The National Vulnerability Database provides the following description for this vulnerability: Authentication Bypass Using an Alternate Path or Channel vulnerability in Apache Tomcat.  When using PreResources or PostResources mounted other than at the root of the web application, it was possible to access those resources via an unexpected path. That path was likely not to be protected by the same security constraints as the expected path, allowing those security constraints to be bypassed.

This issue affects Apache Tomcat: from 11.0.0-M1 through 11.0.7, from 10.1.0-M1 through 10.1.41, from 9.0.0.M1 through 9.0.105.
The following versions were EOL at the time the CVE was created but are
known to be affected: 8.5.0 through 8.5.100. Other, older, EOL versions
may also be affected.

Users are recommended to upgrade to version 11.0.8, 10.1.42 or 9.0.106, which fix the issue.