Possible resource exhaustation of `expandvars` in `Tools/freeze/checkextensions.py`

Bug Description:
The code will re-scan the newly generated content after replacing the variable. If a variable is defined to contain itself (i.e., a recursive definition), this process will fall into infinite recursion.

This recursion can lead to two forms of attacks: one is to cause an infinite loop and deplete CPU resources, and the other is to cause the string to grow infinitely and deplete memory resources. The final result will all lead to the application crashing or being unresponsive.

Vulnerability Locations :
1.https://github.com/python/cpython/blob/e64395e8eb8d3a9e35e3e534e87d427ff27ab0a5/Tools/freeze/checkextensions.py#L72

Repair Status:
None

Common Information:

• CPython Version: main branch
• Operating System: Linux
• Credits: Finder is kexinoh (Xiangfan Wu) from QI-ANXIN Technology Research Institute.

Linked PRs

• gh-136093

Commencez dans Tools/freeze/checkextensions.py, vers la ligne 72, où expandvars réanalyse le contenu généré après le remplacement des variables. Reproduisez une définition de variable autoréférentielle et examinez le travail lié gh-136093 ; le travail est terminé lorsque l’expansion récursive n’épuise plus le CPU ou la mémoire et que le comportement existant reste intact.