This High severity SSRF (Server-Side Request Forgery) vulnerability was introduced in version 9.4.12 of Bitbucket Data Center.

This SSRF (Server-Side Request Forgery) 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:N/I:H/A:N allows an unauthenticated attacker to access the content of internal network resources. When running in an environment like Amazon EC2, this flaw may be used to access a metadata resource that provides access credentials and other potentially confidential information which has no impact to confidentiality, high impact to integrity, no impact to availability, and requires no user interaction.

Atlassian recommends that Bitbucket 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:

• Bitbucket Data Center 9.4: Upgrade to a release greater than or equal to 9.4.23

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

The National Vulnerability Database provides the following description for this vulnerability: fast-uri is a URI parser for Node.js. During parsing it runs a legacy decoding pass over the scheme component and never re-escapes the result, and serialization writes the scheme back out verbatim, unlike the host component which is re-escaped. As a result an input whose scheme carries percent-encoded slashes parses as a scheme with no authority, so the parsed host and error are both undefined, yet resolving or normalizing that same input emits a network-path reference whose authority is attacker-chosen and re-parses to that host. An application that allowlists on the parsed host, or treats a reference with no authority as safe to resolve against its base, gets the opposite of what it checked, giving an off-site redirect, server-side request forgery, or address-policy bypass. The legacy decoder also expands non-standard escape forms, widening the issue past upstream filters, and control characters in the scheme can reach the output as raw carriage return and line feed. The affected versions are 2.3.1 up to but not including 2.4.5, 3.0.0 up to but not including 3.1.6, and 4.0.0 up to but not including 4.1.3. The issue is fixed in 2.4.5, 3.1.6, and 4.1.3, which reject a scheme that is not valid after decoding. Users should upgrade to a patched version.