In order to decrypt SM2 encrypted data an application is expected to call the API function EVP_PKEY_decrypt(). Typically an application will call this function twice. The first time, on entry, the "out" parameter can be NULL and, on exit, the "outlen" parameter is populated with the buffer size required to hold the decrypted plaintext. The application can then allocate a sufficiently sized buffer and call EVP_PKEY_decrypt() again, but this time passing a non-NULL value for the "out" parameter. A bug in the implementation of the SM2 decryption code means that the calculation of the buffer size required to hold the plaintext returned by the first call to EVP_PKEY_decrypt() can be smaller than the actual size required by the second call. This can lead to a buffer overflow when EVP_PKEY_decrypt() is called by the application a second time with a buffer that is too small. A malicious attacker who is able present SM2 content for decryption to an application could cause attacker chosen data to overflow the buffer by up to a maximum of 62 bytes altering the contents of other data held after the buffer, possibly changing application behaviour or causing the application to crash. The location of the buffer is application dependent but is typically heap allocated. Fixed in OpenSSL 1.1.1l (Affected 1.1.1-1.1.1k).

ASN.1 strings are represented internally within OpenSSL as an ASN1_STRING structure which contains a buffer holding the string data and a field holding the buffer length. This contrasts with normal C strings which are repesented as a buffer for the string data which is terminated with a NUL (0) byte. Although not a strict requirement, ASN.1 strings that are parsed using OpenSSL's own "d2i" functions (and other similar parsing functions) as well as any string whose value has been set with the ASN1_STRING_set() function will additionally NUL terminate the byte array in the ASN1_STRING structure. However, it is possible for applications to directly construct valid ASN1_STRING structures which do not NUL terminate the byte array by directly setting the "data" and "length" fields in the ASN1_STRING array. This can also happen by using the ASN1_STRING_set0() function. Numerous OpenSSL functions that print ASN.1 data have been found to assume that the ASN1_STRING byte array will be NUL terminated, even though this is not guaranteed for strings that have been directly constructed. Where an application requests an ASN.1 structure to be printed, and where that ASN.1 structure contains ASN1_STRINGs that have been directly constructed by the application without NUL terminating the "data" field, then a read buffer overrun can occur. The same thing can also occur during name constraints processing of certificates (for example if a certificate has been directly constructed by the application instead of loading it via the OpenSSL parsing functions, and the certificate contains non NUL terminated ASN1_STRING structures). It can also occur in the X509_get1_email(), X509_REQ_get1_email() and X509_get1_ocsp() functions. If a malicious actor can cause an application to directly construct an ASN1_STRING and then process it through one of the affected OpenSSL functions then this issue could be hit. This might result in a crash (causing a Denial of Service attack). It could also result in the disclosure of private memory contents (such as private keys, or sensitive plaintext). Fixed in OpenSSL 1.1.1l (Affected 1.1.1-1.1.1k). Fixed in OpenSSL 1.0.2za (Affected 1.0.2-1.0.2y).

Las cadenas ASN.1 se representan internamente en OpenSSL como una estructura ASN1_STRING que contiene un búfer que contiene los datos de la cadena y un campo que contiene la longitud del búfer. Esto contrasta con las cadenas C normales, que se representan como un búfer para los datos de la cadena que termina con un byte NUL (0). Aunque no es un requisito estricto, las cadenas ASN.1 que se analizan usando las propias funciones "d2i" de OpenSSL (y otras funciones de análisis similares), así como cualquier cadena cuyo valor ha sido ajustado con la función ASN1_STRING_set(), terminarán adicionalmente con NUL la matriz de bytes en la estructura ASN1_STRING. Sin embargo, es posible que las aplicaciones construyan directamente estructuras ASN1_STRING válidas que no terminen en NUL la matriz de bytes, ajustando directamente los campos "data" y "length" en la matriz ASN1_STRING. Esto también puede ocurrir usando la función ASN1_STRING_set0(). Se ha detectado que numerosas funciones de OpenSSL que imprimen datos ASN.1 asumen que la matriz de bytes ASN1_STRING estará terminada en NUL, aunque esto no está garantizado para las cadenas que han sido construidas directamente. Cuando una aplicación pide que se imprima una estructura ASN.1, y cuando esa estructura ASN.1 contiene ASN1_STRINGs que han sido construidos directamente por la aplicación sin terminar en NUL el campo "data", entonces puede ocurrir un desbordamiento del buffer de lectura. Lo mismo puede ocurrir durante el procesamiento de las restricciones de nombre de los certificados (por ejemplo, si un certificado ha sido construido directamente por la aplicación en lugar de cargarlo por medio de las funciones de análisis de OpenSSL, y el certificado contiene estructuras ASN1_STRING sin terminación NUL). También puede ocurrir en las funciones X509_get1_email(), X509_REQ_get1_email() y X509_get1_ocsp(). Si un actor malicioso puede hacer que una aplicación construya directamente un ASN1_STRING y luego lo procese a mediante una de las funciones de OpenSSL afectadas, este problema podría ser alcanzado. Esto podría resultar en un bloqueo (causando un ataque de Denegación de Servicio). También podría resultar en la revelación de contenidos de memoria privada (como claves privadas, o texto plano confidencial). Corregido en OpenSSL versión 1.1.1l (Afectada 1.1.1-1.1.1k). Corregido en OpenSSL versión 1.0.2za (Afectada 1.0.2-1.0.2y).