This is a vulnerability in a non-Atlassian dependency. Atlassian's application of this dependency presents a lower, non-critical assessed risk.

This Critical severity HTTP Request Smuggling vulnerability was introduced in versions 6.2.0, 6.3.0, 7.0.0, 7.1.0, 7.2.0 of Crowd Data Center.
 
This HTTP Request Smuggling vulnerability, with a CVSS Score of 9.8 and a CVSS Vector of CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H allows an unauthenticated attacker to expose assets in your environment susceptible to exploitation which has high impact to confidentiality, high impact to integrity, high impact to availability, and requires no user interaction.
 
Atlassian recommends that Crowd Data Center customers upgrade to latest version, if you are unable to do so, upgrade your instance to one of the specified supported fixed versions:

• Crowd Data Center and Server 7.2: Upgrade to a release greater than or equal to 7.2.1

See the release notes (https://confluence.atlassian.com/crowd/crowd-release-notes-199094.html). You can download the latest version of Crowd Data Center from the download center (https://www.atlassian.com/software/crowd/download-archive).
 
The National Vulnerability Database provides the following description for this vulnerability:
Netty is an asynchronous, event-driven network application framework. Prior to 4.2.13.Final and 4.1.133.Final, HttpObjectDecoder strips a conflicting Content-Length header when a request carries both Transfer-Encoding: chunked and Content-Length, but only for HTTP/1.1 messages. The guard is absent for HTTP/1.0. An attacker that sends an HTTP/1.0 request with both headers causes Netty to decode the body as chunked while leaving Content-Length intact in the forwarded HttpMessage. Any downstream proxy or handler that trusts Content-Length over Transfer-Encoding will disagree on message boundaries, enabling request smuggling. This vulnerability is fixed in 4.2.13.Final and 4.1.133.Final.