In an X.509 certificate, a basicConstraints extension where the cA
field (BOOLEAN) is omitted but the pathLenConstraint field (INTEGER )is
present is syntactically valid, but RFC 5280 states that CAs MUST NOT emit
such a certificate.
Historically, since XySSL 0.9 in 2008, if a basicConstraints extension
started with an INTEGER field, we interpreted that field as a cA value. This
was a deliberate change:
> Fixed x509_get_ext() to accept some rare certificates (like
> www.openssl.org:443) which have an INTEGER instead of a BOOLEAN for
> Extension::BasicConstraints::cA.
However, 18 years later, this does not seem to be relevant, and the details
seem to have been lost. Furthermore, major implementations follow RFC 5280
and interpret `SEQUENCE { INTEGER n }` with cA being set to its default
value (FALSE) and pathLenConstraint set to `n`. This means that such a
certificate with n != 0 would be interpreted as a CA certificate in Mbed TLS
but as a leaf certificate elsewhere, which is dangerous.
Since CAs are not supposed to emit such certificates, stop accepting them
altogether.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
In test cases for pathLenConstraint parsing in a basicConstraints extension
of an X.509 certificate, use the standard type for the leading cA field,
namely BOOLEAN. The test data was encoding that field as INTEGER, which was
accepted as a deviation from the standard since XySSL 0.9.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
It is now unreachable because:
- end_set == end_attr_data is enforced at library/x509_csr.c:236.
- end_exts == end_set is enforced at library/x509_csr.c:248.
- x509_csr_parse_extensions() only returns success if *p == end_exts, enforced
at library/x509_csr.c:188.
So after a successful x509_csr_parse_extensions() call, *p == end_exts ==
end_set == end_attr_data. The condition at line 257 cannot be true.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
Don't allow parts of a compound (SEQUENCE or SET) to go beyond the
containing compound.
The inline CSR regression test is derived from the existing "X509 CSR
ASN.1 (OK)" DER test vector. In the extensionRequest attribute, the original
well-formed fragment is:
a029 3027 06092a864886f70d01090e 311a 3018 ...
where 31 1a is the SET containing the Extensions sequence and 30 18 is the
contained Extensions sequence. The malformed test changes only the SET
length byte, from 1a to 19:
a029 3027 06092a864886f70d01090e 3119 3018 ...
The attribute SEQUENCE length and the inner Extensions sequence length are
left unchanged. This makes the SET one byte too short for its containing
attribute, so the parser must reject it with
MBEDTLS_ERR_ASN1_LENGTH_MISMATCH instead of parsing the trailing byte as
data outside the SET.
There is no known security impact, just some risk reduction.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
I believe the existing link was to the TF wiki which has been retired
for some time now.
Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
When parsing the basicConstraints extension, reject junk after the SEQUENCE
inside the extension (which is probably benign), and reject a SEQUENCE that
extends beyond the extension (could be very dangerous).
Add a non-regression test where a certificate that is technically malformed,
but accepted as a leaf certificate by OpenSSL and other X.509
implementations, to be accepted as a CA certificate by Mbed TLS.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
Clarify that the 'sig_algs' set through this function are only enforced
during the key exchange and that 'mbedtls_ssl_conf_cert_profile()' should
instead be used to enforce the same algorithms when verifying certificates.
Signed-off-by: Valerio Setti <vsetti@baylibre.com>
Previously this was tested indirectly by comparing driver vs reference
components in analyze-outcomes.py, but now that the number of exceptions
is low, it's much more efficient to test this directly.
Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
Also remove the "no USE_PSA" tests: they are not executed, and are not
useful for the future - when we add support for restartable ECDH in TLS,
we can just use the existing tests and update the assertions, which
we'll have to do anyway (the tests being removed were asserting about
a legacy crypto function that no longer exists).
Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
