Potential Quadratic Complexity Vulnerabilities in the `email` Module

[kexinoh]

Bug Description:
A series of simple quadratic complexity vulnerabilities has been identified in the email package. After confirmation by CPython's security team, these low-threat DOS vulnerabilities can be fixed with community assistance.

Vulnerability Locations (All Fixed):

1. cpython/Lib/email/message.py

   Line 73 in 5ab66a8

   def _parseparam(s):

   
   2.

   cpython/Lib/email/_header_value_parser.py

   Line 1424 in 5ab66a8

   def get_phrase(value):

   
   3.

   cpython/Lib/email/_header_value_parser.py

   Line 1506 in 5ab66a8

   while value and (value[0]=='\\' or value[0] not in PHRASE_ENDS):

   
   4.

   cpython/Lib/email/_header_value_parser.py

   Line 1688 in 5ab66a8

   value = value[1:]

   
   5.

   cpython/Lib/email/_header_value_parser.py

   Line 1697 in 5ab66a8

   value = value[1:]

   
   6.

   cpython/Lib/email/_header_value_parser.py

   Line 1847 in 5ab66a8

   value = value[1:]

   
   7.

   cpython/Lib/email/_header_value_parser.py

   Line 2200 in 5ab66a8

   value = value[1:]

   
   8.

   cpython/Lib/email/_header_value_parser.py

   Line 2231 in 5ab66a8

   value = value[1:]

   
   9.

   cpython/Lib/email/_header_value_parser.py

   Line 2260 in 5ab66a8

   value = value[1:]

   
   10.

   cpython/Lib/email/_header_value_parser.py

   Line 2411 in 5ab66a8

   value = value[1:]

   
   11.

   cpython/Lib/email/_header_value_parser.py

   Line 2570 in 5ab66a8

   value = value[1:]

   
   12.

   cpython/Lib/email/_header_value_parser.py

   Line 2642 in 5ab66a8

   value = value[1:]

   
   13.

   cpython/Lib/email/_header_value_parser.py

   Line 2762 in 5ab66a8

   value = value[1:]

   
   14.

   cpython/Lib/email/_header_value_parser.py

   Line 2965 in 5ab66a8

   to_encode = to_encode[1:]

Repair Status:

• @picnixz is currently fixing all listed vulnerabilities in the email package (gh-136063: fix various quadratic worst-time complexities in _header_value_parser.py [WIP] #134947).

Common Information:

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

Linked PRs

• gh-136063: fix various quadratic worst-time complexities in _header_value_parser.py [WIP] #134947
• gh-136063: fix quadratic-complexity parsing in email.message._parseparam #136072

[picnixz]

To be precise, I still didn't fix everything. There are subtle cases that may require an entire module rewrite.

[kexinoh]

Ok. I revised the expression