This High severity BASM (Broken Authentication & Session Management) vulnerability was introduced in version 4.9.0 of Crucible Server.

This BASM (Broken Authentication & Session Management) vulnerability, with a CVSS Score of 8.1 and a CVSS Vector of CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N allows an authenticated attacker to expose assets in your environment susceptible to exploitation, which has high impact to confidentiality, high impact to integrity, no impact to availability, and requires no user interaction.

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

• Crucible Server 4.9: Upgrade to a release greater than or equal to 4.9.15

See the release notes (https://confluence.atlassian.com/crucible/crucible-releases-298977378.html). You can download the
latest version of Crucible Server from the download center
(https://www.atlassian.com/software/crucible/download-archives).

The National Vulnerability Database provides the following description for this vulnerability:

Apache MINA SSHD is a Java library for client-side and server-side SSH. SSH servers can be configured to require multi-authentication schemes, for instance two different public keys, not just one. In OpenSSH, this would be done by setting in sshd_config AuthenticationMethods "publickey,publickey". Apache MINA SSHD provides an equivalent configuration mechanism.

In Apache MINA SSHD versions up to 2.19.0 and 3.0.0-M1 to 3.0.0-M5 the server code in component sshd-core does not enforce that the two public keys presented are different. A user can thus successfully authenticate with only one of the two key pairs required by presenting this single key twice. This is a partial authentication bypass.

Users are recommended to upgrade to version 2.20.0 or 3.0.0-M6, which fix this issue.