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pe.signatures[i].hashinvalid #1290

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pe.signatures[i].hashinvalid #1290

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dbd5891
Solving linking error for Openssl > 1.1
soumy May 18, 2020
6325c0f
Adding per certificate file hash validation on PE file.
soumy May 21, 2020
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160 changes: 158 additions & 2 deletions libyara/modules/pe/pe.c
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Original file line number Diff line number Diff line change
Expand Up @@ -35,6 +35,7 @@ SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
#if defined(HAVE_LIBCRYPTO)
#include <openssl/safestack.h>
#include <openssl/asn1.h>
#include <openssl/asn1t.h>
#include <openssl/bio.h>
#include <openssl/pkcs7.h>
#include <openssl/x509.h>
Expand Down Expand Up @@ -1276,6 +1277,128 @@ static void pe_parse_exports(
// but you won't have signature-related features in the PE module.
#if defined(HAVE_LIBCRYPTO) && !defined(BORINGSSL)

#define SPC_INDIRECT_DATA_OBJID "1.3.6.1.4.1.311.2.1.4"

typedef struct {
ASN1_OBJECT *type;
ASN1_TYPE *value;
} SpcAttributeTypeAndOptionalValue;

DECLARE_ASN1_FUNCTIONS(SpcAttributeTypeAndOptionalValue)

ASN1_SEQUENCE(SpcAttributeTypeAndOptionalValue) = {
ASN1_SIMPLE(SpcAttributeTypeAndOptionalValue, type, ASN1_OBJECT),
ASN1_OPT(SpcAttributeTypeAndOptionalValue, value, ASN1_ANY)
} ASN1_SEQUENCE_END(SpcAttributeTypeAndOptionalValue)

IMPLEMENT_ASN1_FUNCTIONS(SpcAttributeTypeAndOptionalValue)

typedef struct {
ASN1_OBJECT *algorithm;
ASN1_TYPE *parameters;
} AlgorithmIdentifier;

DECLARE_ASN1_FUNCTIONS(AlgorithmIdentifier)

ASN1_SEQUENCE(AlgorithmIdentifier) = {
ASN1_SIMPLE(AlgorithmIdentifier, algorithm, ASN1_OBJECT),
ASN1_OPT(AlgorithmIdentifier, parameters, ASN1_ANY)
} ASN1_SEQUENCE_END(AlgorithmIdentifier)

IMPLEMENT_ASN1_FUNCTIONS(AlgorithmIdentifier)

typedef struct {
AlgorithmIdentifier *digestAlgorithm;
ASN1_OCTET_STRING *digest;
} DigestInfo;

DECLARE_ASN1_FUNCTIONS(DigestInfo)

ASN1_SEQUENCE(DigestInfo) = {
ASN1_SIMPLE(DigestInfo, digestAlgorithm, AlgorithmIdentifier),
ASN1_SIMPLE(DigestInfo, digest, ASN1_OCTET_STRING)
} ASN1_SEQUENCE_END(DigestInfo)

IMPLEMENT_ASN1_FUNCTIONS(DigestInfo)

typedef struct {
SpcAttributeTypeAndOptionalValue *data;
DigestInfo *messageDigest;
} SpcIndirectDataContent;

DECLARE_ASN1_FUNCTIONS(SpcIndirectDataContent)

ASN1_SEQUENCE(SpcIndirectDataContent) = {
ASN1_SIMPLE(SpcIndirectDataContent, data, SpcAttributeTypeAndOptionalValue),
ASN1_SIMPLE(SpcIndirectDataContent, messageDigest, DigestInfo)
} ASN1_SEQUENCE_END(SpcIndirectDataContent)

IMPLEMENT_ASN1_FUNCTIONS(SpcIndirectDataContent)

static int is_indirect_data_signature(PKCS7 *p7)
{
ASN1_OBJECT *indir_objid;
int retval;

indir_objid = OBJ_txt2obj(SPC_INDIRECT_DATA_OBJID, 1);
retval = p7 && PKCS7_type_is_signed(p7) &&
!OBJ_cmp(p7->d.sign->contents->type, indir_objid) &&
p7->d.sign->contents->d.other->type == V_ASN1_SEQUENCE;
ASN1_OBJECT_free(indir_objid);
return retval;
}

static void tohex(const unsigned char *v, char *b, int len)
{
int i;
for (i = 0; i < len; i++)
sprintf(b + i * 2, "%02X", v[i]);
}

//From osslsigncode
static void pe_calc_digest(BIO *bio, const EVP_MD *md, unsigned char *mdbuf, PE* pe)
{
size_t sizebfb = 16 * 1024 * 1024;
unsigned char* bfb = malloc(sizebfb);
EVP_MD_CTX *mdctx;
size_t n;
size_t headersize = yr_le32toh(((PIMAGE_DOS_HEADER)pe->data)->e_lfanew);
size_t pe32plus = IS_64BITS_PE(pe);
PIMAGE_DATA_DIRECTORY directory = pe_get_directory_entry(
pe, IMAGE_DIRECTORY_ENTRY_SECURITY);
size_t sigpos = yr_le32toh(directory->VirtualAddress);
int l;

mdctx = EVP_MD_CTX_new();
EVP_DigestInit(mdctx, md);
memset(mdbuf, 0, EVP_MAX_MD_SIZE);
memset(bfb, 0, sizebfb);

(void)BIO_seek(bio, 0);
BIO_read(bio, bfb, (headersize + 88));
EVP_DigestUpdate(mdctx, bfb, (headersize + 88));
BIO_read(bio, bfb, 4); //Skip the header checksum. Read from bio but don't update the ctx
BIO_read(bio, bfb, (60 + pe32plus * 16));
EVP_DigestUpdate(mdctx, bfb, (60 + pe32plus * 16));
BIO_read(bio, bfb, 8); //Skip IMAGE_DIRECTORY_ENTRY_SECURITY size

n = headersize + 88 + 4 + 60 + (pe32plus * 16) + 8;

while (n < sigpos) {
size_t want = sigpos - n;
if (want > sizebfb)
want = sizebfb;
l = BIO_read(bio, bfb, want);
if (l <= 0)
break;
EVP_DigestUpdate(mdctx, bfb, l);
n += l;
}
EVP_DigestFinal(mdctx, mdbuf, NULL);
EVP_MD_CTX_free(mdctx);
free(bfb);
}

//
// Parse a PKCS7 blob, looking for certs and nested PKCS7 blobs.
//
Expand Down Expand Up @@ -1305,6 +1428,11 @@ void _parse_pkcs7(
STACK_OF(X509)* certs = NULL;
X509_ATTRIBUTE *xa = NULL;
STACK_OF(X509_ATTRIBUTE)* attrs = NULL;
const EVP_MD *md;
char hexbuf[EVP_MAX_MD_SIZE * 2 + 1];
unsigned char mdbuf[EVP_MAX_MD_SIZE] = { 0 }, cmdbuf[EVP_MAX_MD_SIZE] = { 0 };
int mdtype = -1;
BIO *bio = NULL;

if (*counter >= MAX_PE_CERTS)
return;
Expand Down Expand Up @@ -1348,6 +1476,33 @@ void _parse_pkcs7(

set_string(sig_alg, pe->object, "signatures[%i].algorithm", *counter);

if (is_indirect_data_signature(pkcs7))
{
ASN1_STRING *astr = pkcs7->d.sign->contents->d.other->value.sequence;
const unsigned char *p = astr->data;
SpcIndirectDataContent *idc = d2i_SpcIndirectDataContent(NULL, &p, astr->length);
if (idc) {
if (idc->messageDigest && idc->messageDigest->digest && idc->messageDigest->digestAlgorithm) {
mdtype = OBJ_obj2nid(idc->messageDigest->digestAlgorithm->algorithm);
if (mdtype != -1) {
memcpy(mdbuf, idc->messageDigest->digest->data, idc->messageDigest->digest->length);

md = EVP_get_digestbynid(mdtype);
tohex(mdbuf, hexbuf, EVP_MD_size(md));
PIMAGE_DATA_DIRECTORY directory = pe_get_directory_entry(
pe, IMAGE_DIRECTORY_ENTRY_SECURITY);
bio = BIO_new_mem_buf(pe->data, yr_le32toh(directory->VirtualAddress) + yr_le32toh(directory->Size));
pe_calc_digest(bio, md, cmdbuf, pe);
BIO_free(bio);
tohex(cmdbuf, hexbuf, EVP_MD_size(md));
int invalid = memcmp(mdbuf, cmdbuf, EVP_MD_size(md)) != 0;
set_integer(invalid, pe->object, "signatures[%i].hashinvalid", *counter);
}
}
SpcIndirectDataContent_free(idc);
}
}

serial = X509_get_serialNumber(cert);

if (serial)
Expand Down Expand Up @@ -1433,10 +1588,10 @@ void _parse_pkcs7(
}
}

date_time = ASN1_get_time_t(X509_get_notBefore(cert));
date_time = ASN1_get_time_t(X509_getm_notBefore(cert));
set_integer(date_time, pe->object, "signatures[%i].not_before", *counter);

date_time = ASN1_get_time_t(X509_get_notAfter(cert));
date_time = ASN1_get_time_t(X509_getm_notAfter(cert));
set_integer(date_time, pe->object, "signatures[%i].not_after", *counter);

(*counter)++;
Expand Down Expand Up @@ -2960,6 +3115,7 @@ begin_declarations;
declare_integer("not_before");
declare_integer("not_after");
declare_function("valid_on", "i", "i", valid_on);
declare_integer("hashinvalid");
end_struct_array("signatures");

declare_integer("number_of_signatures");
Expand Down