The public API function BIO_new_NDEF is a helper function used for streaming
ASN.1 data via a BIO. It is primarily used internally to OpenSSL to support the
SMIME, CMS and PKCS7 streaming capabilities, but may also be called directly by
end user applications.
The function receives a BIO from the caller, prepends a new BIO_f_asn1 filter
BIO onto the front of it to form a BIO chain, and then returns the new head of
the BIO chain to the caller. Under certain conditions, for example if a CMS
recipient public key is invalid, the new filter BIO is freed and the function
returns a NULL result indicating a failure. However, in this case, the BIO chain
is not properly cleaned up and the BIO passed by the caller still retains
internal pointers to the previously freed filter BIO. If the caller then goes on
to call BIO_pop() on the BIO then a use-after-free will occur. This will most
likely result in a crash.
This scenario occurs directly in the internal function B64_write_ASN1() which
may cause BIO_new_NDEF() to be called and will subsequently call BIO_pop() on
the BIO. This internal function is in turn called by the public API functions
PEM_write_bio_ASN1_stream, PEM_write_bio_CMS_stream, PEM_write_bio_PKCS7_stream,
SMIME_write_ASN1, SMIME_write_CMS and SMIME_write_PKCS7.
Other public API functions that may be impacted by this include
i2d_ASN1_bio_stream, BIO_new_CMS, BIO_new_PKCS7, i2d_CMS_bio_stream and
i2d_PKCS7_bio_stream.
The OpenSSL cms and smime command line applications are similarly affected.
An invalid pointer dereference on read can be triggered when an
application tries to load malformed PKCS7 data with the
d2i_PKCS7(), d2i_PKCS7_bio() or d2i_PKCS7_fp() functions.
The result of the dereference is an application crash which could
lead to a denial of service attack. The TLS implementation in OpenSSL
does not call this function however third party applications might
call these functions on untrusted data.
There is a type confusion vulnerability relating to X.400 address processing
inside an X.509 GeneralName. X.400 addresses were parsed as an ASN1_STRING but
the public structure definition for GENERAL_NAME incorrectly specified the type
of the x400Address field as ASN1_TYPE. This field is subsequently interpreted by
the OpenSSL function GENERAL_NAME_cmp as an ASN1_TYPE rather than an
ASN1_STRING.
When CRL checking is enabled (i.e. the application sets the
X509_V_FLAG_CRL_CHECK flag), this vulnerability may allow an attacker to pass
arbitrary pointers to a memcmp call, enabling them to read memory contents or
enact a denial of service. In most cases, the attack requires the attacker to
provide both the certificate chain and CRL, neither of which need to have a
valid signature. If the attacker only controls one of these inputs, the other
input must already contain an X.400 address as a CRL distribution point, which
is uncommon. As such, this vulnerability is most likely to only affect
applications which have implemented their own functionality for retrieving CRLs
over a network.
A NULL pointer can be dereferenced when signatures are being
verified on PKCS7 signed or signedAndEnveloped data. In case the hash
algorithm used for the signature is known to the OpenSSL library but
the implementation of the hash algorithm is not available the digest
initialization will fail. There is a missing check for the return
value from the initialization function which later leads to invalid
usage of the digest API most likely leading to a crash.
The unavailability of an algorithm can be caused by using FIPS
enabled configuration of providers or more commonly by not loading
the legacy provider.
PKCS7 data is processed by the SMIME library calls and also by the
time stamp (TS) library calls. The TLS implementation in OpenSSL does
not call these functions however third party applications would be
affected if they call these functions to verify signatures on untrusted
data.
The Diffie-Hellman Key Agreement Protocol allows remote attackers (from the client side) to send arbitrary numbers that are actually not public keys, and trigger expensive server-side DHE modular-exponentiation calculations, aka a D(HE)at or D(HE)ater attack. The client needs very little CPU resources and network bandwidth. The attack may be more disruptive in cases where a client can require a server to select its largest supported key size. The basic attack scenario is that the client must claim that it can only communicate with DHE, and the server must be configured to allow DHE.