Gives error parsing asn1 value on a field i'm not trying to get

[swamp-fish]

I'm trying to access Subject Key Identifier field:

with open(der_cert, "rb") as f:
    data = f.read()
try:
    cert = x509.load_pem_x509_certificate(data, default_backend())
except ValueError:
    cert = x509.load_der_x509_certificate(data, default_backend())

cert.extensions.get_extension_for_oid(
            ExtensionOID.SUBJECT_KEY_IDENTIFIER
        ).value

Here's an error its giving me:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: error parsing asn1 value: ParseError { kind: InvalidValue, location: ["subject_alternative_name", 0, "GeneralName::RFC822Name"] }

However i don't try to parse subject_alternative_name, i don't need it.

It gives me an error on cert.extensions already. However i think it should ignore other fields if i specifically ask for something specific such as Subject Key Identifier.

If i use GUI certificate viewer on KDE it shows everything. And PyOpenSSL also doesn't give an error.

with open(der_cert, 'rb+') as f:
    cert_pem = f.read()
f.close()
cert = load_certificate(FILETYPE_ASN1, cert_pem)

for i in range(extension_count):
    extension = cert.get_extension(i)
    if extension.get_short_name() == b'subjectKeyIdentifier':
        subject_key_identifier = hexlify(extension.get_data()).decode()[4:]
        print(subject_key_identifier)

Here's a certificate for testing:
EU-59F1280800000000000000000000000000000001.cer.txt

[alex]

When extensions are accessed, all extensions are parsed and therefore must be valid.

@reaperhulk I remember us discussing this issue a number of years ago, and clearly we haven't taken action on it. Do you remember our reasoning?