The asn1_get_bit_der function in GNU Libtasn1 before 3.6 does not properly report an error when a negative bit length is identified, which allows context-dependent attackers to cause out-of-bounds access via crafted ASN.1 data. diff --git a/lib/decoding.c b/lib/decoding.c index 7e0ed05..894be79 100644 --- a/lib/decoding.c +++ b/lib/decoding.c @@ -249,7 +249,7 @@ asn1_get_octet_der (const unsigned char *der, int der_len, int *ret_len, unsigned char *str, int str_size, int *str_len) { - int len_len; + int len_len = 0; if (der_len <= 0) return ASN1_GENERIC_ERROR; @@ -371,7 +371,7 @@ asn1_get_bit_der (const unsigned char *der, int der_len, int *ret_len, unsigned char *str, int str_size, int *bit_len) { - int len_len, len_byte; + int len_len = 0, len_byte; if (der_len <= 0) return ASN1_GENERIC_ERROR; @@ -381,6 +381,9 @@ asn1_get_bit_der (const unsigned char *der, int der_len, *ret_len = len_byte + len_len + 1; *bit_len = len_byte * 8 - der[len_len]; + + if (*bit_len <= 0) + return ASN1_DER_ERROR; if (str_size >= len_byte) memcpy (str, der + len_len + 1, len_byte);