Subject Decoding NameError

[sargeant]

Variable fixed_subject is only assigned inside a try block. If decoding raises an exception, the code attempts to return undefined fixed_subject, causing a NameError that crashes the milter handler.

Emails with malformed subject headers cause milter crashes, blocking email delivery.

File: src/milter/processor.py:158-170

Current Code

if mail_subject:
    try:
        fixed_subject = bytes(decode_header(mail_subject)[0][0]).decode(decode_header(mail_subject)[0][1])
    except:
        fixed_subject = mail_subject

try:
    return (fixed_subject, mail_headers)
except NameError:
    return ('', mail_headers)

Recommended Fix

fixed_subject = mail_subject  # default value
if mail_subject:
    try:
        decoded = decode_header(mail_subject)[0]
        if decoded[1]:
            fixed_subject = decoded[0].decode(decoded[1])
        else:
            fixed_subject = decoded[0] if isinstance(decoded[0], str) else decoded[0].decode('utf-8')
    except Exception as e:
        logger.warning(f"Failed to decode subject header: {e}")

return (fixed_subject if fixed_subject else '', mail_headers)

Testing

Need to test with emails containing:

1. Valid UTF-8 subject headers
2. ISO-8859-1 encoded subjects
3. Malformed encoding declarations
4. Missing subject headers
5. Subject headers with invalid byte sequences