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Allow validating V3 certificates that have no extensions #34

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Feb 23, 2023
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56 changes: 27 additions & 29 deletions src/cert.rs
Original file line number Diff line number Diff line change
Expand Up @@ -95,35 +95,33 @@ pub(crate) fn parse_cert_internal<'a>(
subject_alt_name: None,
};

// mozilla::pkix allows the extensions to be omitted. However, since
// the subjectAltName extension is mandatory, the extensions are
// mandatory too, and we enforce that. Also, mozilla::pkix includes
// special logic for handling critical Netscape Cert Type extensions.
// That has been intentionally omitted.

der::nested(
tbs,
der::Tag::ContextSpecificConstructed3,
Error::MissingOrMalformedExtensions,
|tagged| {
der::nested_of_mut(
tagged,
der::Tag::Sequence,
der::Tag::Sequence,
Error::BadDer,
|extension| {
let extn_id = der::expect_tag_and_get_value(extension, der::Tag::OID)?;
let critical = der::optional_boolean(extension)?;
let extn_value =
der::expect_tag_and_get_value(extension, der::Tag::OctetString)?;
match remember_extension(&mut cert, extn_id, extn_value)? {
Understood::No if critical => Err(Error::UnsupportedCriticalExtension),
_ => Ok(()),
}
},
)
},
)?;
if !tbs.at_end() {
der::nested(
tbs,
der::Tag::ContextSpecificConstructed3,
Error::MalformedExtensions,
|tagged| {
der::nested_of_mut(
tagged,
der::Tag::Sequence,
der::Tag::Sequence,
Error::BadDer,
|extension| {
let extn_id = der::expect_tag_and_get_value(extension, der::Tag::OID)?;
let critical = der::optional_boolean(extension)?;
let extn_value =
der::expect_tag_and_get_value(extension, der::Tag::OctetString)?;
match remember_extension(&mut cert, extn_id, extn_value)? {
Understood::No if critical => {
Err(Error::UnsupportedCriticalExtension)
}
_ => Ok(()),
}
},
)
},
)?;
}

Ok(cert)
})
Expand Down
4 changes: 2 additions & 2 deletions src/error.rs
Original file line number Diff line number Diff line change
Expand Up @@ -74,12 +74,12 @@ pub enum Error {
/// is malformed.
UnsupportedCertVersion,

/// The certificate extensions are missing or malformed.
/// The certificate extensions are malformed.
///
/// In particular, webpki requires the DNS name(s) be in the subjectAltName
/// extension as required by the CA/Browser Forum Baseline Requirements
/// and as recommended by RFC6125.
MissingOrMalformedExtensions,
MalformedExtensions,

/// The certificate contains an unsupported critical extension.
UnsupportedCriticalExtension,
Expand Down
5 changes: 1 addition & 4 deletions tests/cert_without_extensions.rs
Original file line number Diff line number Diff line change
Expand Up @@ -20,8 +20,5 @@ fn cert_without_extensions_test() {
// `openssl x509 -in cert_without_extensions.der -inform DER -text -noout`
const CERT_WITHOUT_EXTENSIONS_DER: &[u8] = include_bytes!("cert_without_extensions.der");

assert_eq!(
Some(webpki::Error::MissingOrMalformedExtensions),
webpki::EndEntityCert::try_from(CERT_WITHOUT_EXTENSIONS_DER).err()
);
assert!(webpki::EndEntityCert::try_from(CERT_WITHOUT_EXTENSIONS_DER).is_ok());
}