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authorPaul Barker <paul@pbarker.dev>2021-06-07 11:02:51 +0100
committerKonstantin Ryabitsev <konstantin@linuxfoundation.org>2021-06-07 08:49:23 -0400
commit366bcd1fd8a10b6125e591f0c35cc85b10c9c950 (patch)
tree182506f7ad4dbf44584802642ad1bf6aa39efbf7
parenta727eaeb9a7183262659b8192fc823e409bba49a (diff)
downloadb4-366bcd1fd8a10b6125e591f0c35cc85b10c9c950.tar.gz
Handle MIME encoded-word in DKIM-Signature headers
As recently found in patatt [1], mail gateways and archivers may mangle headers like DKIM-Signature if they are sent as an excessively long line. An example of this occuring was found when the DKIM-Signature header generated by Microsoft Office 365 collided with the header re-encoding performed by lists.sr.ht when generating mbox archive files. This encoding causes dkim.verify() to fail. The Python email.header module provides the decode_header() and make_header() functions which can be used to handle MIME encoded-word syntax or other header manglings which may occur. Fixing up the header content using these functions before calling dkim.verify() allows the verification to succeed. [1]: https://lore.kernel.org/tools/20210531140539.7630-1-paul@pbarker.dev/ Signed-off-by: Paul Barker <paul@pbarker.dev> Signed-off-by: Konstantin Ryabitsev <konstantin@linuxfoundation.org> Link: https://lore.kernel.org/r/20210607100252.8253-2-paul@pbarker.dev
-rw-r--r--b4/__init__.py4
1 files changed, 4 insertions, 0 deletions
diff --git a/b4/__init__.py b/b4/__init__.py
index a163364..168b722 100644
--- a/b4/__init__.py
+++ b/b4/__init__.py
@@ -1006,6 +1006,10 @@ class LoreMessage:
seenatts = list()
for hn, hval in dkhdrs:
+ # Handle MIME encoded-word syntax or other types of header encoding if
+ # present.
+ if '?q?' in hval:
+ hval = str(email.header.make_header(email.header.decode_header(hval)))
errors = list()
hdata = LoreMessage.get_parts_from_header(hval)
logger.debug('Loading DKIM attestation for d=%s, s=%s', hdata['d'], hdata['s'])