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gh-80222: Fix email address header folding with long quoted-string #122753

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Merged
bitdancer merged 4 commits into from
Jan 19, 2025
Merged

gh-80222: Fix email address header folding with long quoted-string #122753

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73f3ffd
gh-80222: Fix email address header folding with long quoted-string
medmunds Aug 6, 2024
4df13d9
Merge branch 'main' into fix-issue-80222
medmunds Oct 21, 2024
c268499
Merge branch 'main' into fix-issue-80222
medmunds Jan 18, 2025
6926474
Address review comments
medmunds Jan 18, 2025
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Address review comments
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@medmunds
medmunds committed Jan 18, 2025
commit 69264749d46df2ad428e56b47cfa685997adacb3
15 changes: 8 additions & 7 deletions Lib/email/_header_value_parser.py
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Original file line number Diff line number Diff line change
Expand Up @@ -96,13 +96,13 @@
SPECIALSNL = SPECIALS | NLSET


def escape_for_quotes(value):
def make_quoted_pairs(value):
"""Escape dquote and backslash for use within a quoted-string."""
return str(value).replace('\\', '\\\\').replace('"', '\\"')


def quote_string(value):
escaped = escape_for_quotes(value)
escaped = make_quoted_pairs(value)
return f'"{escaped}"'


Expand Down Expand Up @@ -2914,13 +2914,14 @@ def _refold_parse_tree(parse_tree, *, policy):
# It's not a terminal, try folding the subparts.
newparts = list(part)
if part.token_type == 'bare-quoted-string':
# Restore the quotes and escape contents.
dquote = ValueTerminal('"', 'ptext')
# To fold a quoted string we need to create a list of terminal
# tokens that will render the leading and trailing quotes
# and use quoted pairs in the value as appropriate.
newparts = (
[dquote] +
[ValueTerminal(escape_for_quotes(p), 'ptext')
[ValueTerminal('"', 'ptext')] +
[ValueTerminal(make_quoted_pairs(p), 'ptext')
for p in newparts] +
[dquote])
[ValueTerminal('"', 'ptext')])
if not part.as_ew_allowed:
wrap_as_ew_blocked += 1
newparts.append(end_ew_not_allowed)
Expand Down
9 changes: 6 additions & 3 deletions Misc/NEWS.d/next/Security/2024-08-06-11-43-08.gh-issue-80222.wfR4BU.rst
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@@ -1,3 +1,6 @@
Fix a problem where email.policy.default header refolding could incorrectly
omit quotes from structured email headers, enabling sender or recipient
spoofing via a carefully crafted display-name.
Fix bug in the folding of quoted strings when flattening an email message using
a modern email policy. Previously when a quoted string was folded so that
it spanned more than one line, the surrounding quotes and internal escapes
would be omitted. This could theoretically be used to spoof header lines
using a carefully constructed quoted string if the resulting rendered email
was transmitted or re-parsed.
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