CVE-2026-46383: Microsoft APM: Windows absolute-path tar member overwrite during legacy-bundle probing in `apm install`

Microsoft APM contains a Windows-specific archive extraction boundary failure in the legacy-bundle probe used by apm install <bundle> on supported Python 3.10 and 3.11 runtimes. When apm install is given a local .tar.gz that is not recognized as a plugin-format bundle, APM probes whether it is a legacy --format apm bundle. On Python versions earlier than 3.12, that probe extracts untrusted tar members with raw tar.extractall() without rejecting Windows absolute member names such as D:/....

This issue is still present on the latest main commit at review time (2b7a931d58a73cbfc0bcf086cea332d204075e27) and on the latest release (v0.12.4). In both cases, a crafted legacy-looking tarball caused an external file to be created or overwritten outside the temporary extraction root before apm install finished rejecting the bundle with the expected legacy-format usage error.

This report is scoped narrowly to Windows installations running Python 3.10 or 3.11.