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Armor regex catastrophic backtracking problem #466

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bwbroersma opened this issue Jul 7, 2024 · 0 comments · May be fixed by #467
Open

Armor regex catastrophic backtracking problem #466

bwbroersma opened this issue Jul 7, 2024 · 0 comments · May be fixed by #467

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@bwbroersma
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bwbroersma commented Jul 7, 2024 •
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The armor regex:

PGPy/pgpy/types.py

Lines 49 to 69 in 30a7571

# the re.VERBOSE flag allows for:
# - whitespace is ignored except when in a character class or escaped
# - anything after a '#' that is not escaped or in a character class is ignored, allowing for comments
__armor_regex = re.compile(r"""# This capture group is optional because it will only be present in signed cleartext messages
(^-{5}BEGIN\ PGP\ SIGNED\ MESSAGE-{5}(?:\r?\n)
(Hash:\ (?P<hashes>[A-Za-z0-9\-,]+)(?:\r?\n){2})?
(?P<cleartext>(.*\r?\n)*(.*(?=\r?\n-{5})))(?:\r?\n)
)?
# armor header line; capture the variable part of the magic text
^-{5}BEGIN\ PGP\ (?P<magic>[A-Z0-9 ,]+)-{5}(?:\r?\n)
# try to capture all the headers into one capture group
# if this doesn't match, m['headers'] will be None
(?P<headers>(^.+:\ .+(?:\r?\n))+)?(?:\r?\n)?
# capture all lines of the body, up to 76 characters long,
# including the newline, and the pad character(s)
(?P<body>([A-Za-z0-9+/]{1,76}={,2}(?:\r?\n))+)
# capture the armored CRC24 value
^=(?P<crc>[A-Za-z0-9+/]{4})(?:\r?\n)
# finally, capture the armor tail line, which must match the armor header line
^-{5}END\ PGP\ (?P=magic)-{5}(?:\r?\n)?
""", flags=re.MULTILINE | re.VERBOSE)

has catastrophic backtracking problems.

See this example on regex101.com, which results in:

Catastrophic backtracking has been detected and the execution of your expression has been halted. To find out more and what this is, please read the following article: Runaway Regular Expressions

The problem are the six dashes (while only 5 are valid PGP):

------BEGIN PGP SIGNATURE-----
------END PGP SIGNATURE-----

which does not match, and because of some nested * capture, there is a backtracking chaos.

After some tweaking I've a regex patch that has the same py39 outcome:
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Fix armor regex catastrophic backtracking bwbroersma/PGPy
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@bwbroersma