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[pki] check timestamp chronology during update validation

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* Done to address the second "vulnerability" proposed in #1009, independently
  of the protocol used.
This commit is contained in:
Pete Batard 2017-09-01 18:27:34 +01:00
parent c3c39f7f8a
commit 35da381a11
6 changed files with 253 additions and 8 deletions
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168
src/pki.c
View file

@ -119,6 +119,8 @@ const char* WinPKIErrorString(void)
return "Not digitally signed.";
case TRUST_E_EXPLICIT_DISTRUST:
return "One of the certificates used was marked as untrusted by the user.";
case TRUST_E_TIME_STAMP:
return "The timestamp could not be verified.";
default:
static_sprintf(error_string, "Unknown PKI error 0x%08lX", error_code);
return error_string;
@ -137,7 +139,6 @@ char* GetSignatureName(const char* path)
PCCERT_CONTEXT pCertContext = NULL;
DWORD dwSize, dwEncoding, dwContentType, dwFormatType, dwSubjectSize;
PCMSG_SIGNER_INFO pSignerInfo = NULL;
PCMSG_SIGNER_INFO pCounterSignerInfo = NULL;
DWORD dwSignerInfo = 0;
CERT_INFO CertInfo = { 0 };
SPROG_PUBLISHERINFO ProgPubInfo = { 0 };
@ -221,7 +222,6 @@ out:
safe_free(ProgPubInfo.lpszPublisherLink);
safe_free(ProgPubInfo.lpszMoreInfoLink);
safe_free(pSignerInfo);
safe_free(pCounterSignerInfo);
if (pCertContext != NULL)
CertFreeCertificateContext(pCertContext);
if (hStore != NULL)
@ -231,6 +231,154 @@ out:
return p;
}
// The timestamping authorities we use are RFC 3161 compliant
static uint64_t GetRFC3161TimeStamp(PCMSG_SIGNER_INFO pSignerInfo)
{
// Binary representation of szOID_TIMESTAMP_TOKEN or "1.2.840.113549.1.9.16.1.4"
const uint8_t OID_RFC3161_timeStamp[] = { 0x2a, 0x86, 0x48, 0x86, 0xf7, 0x0d, 0x01, 0x09, 0x10, 0x01, 0x04 };
BOOL r;
DWORD n, dwSize;
PCRYPT_CONTENT_INFO pCounterSignerInfo = NULL;
uint64_t ts = 0ULL;
uint8_t *timestamp_token;
size_t timestamp_token_size;
char* timestamp_str;
size_t timestamp_str_size;
// Loop through unathenticated attributes for szOID_RFC3161_counterSign OID
for (n = 0; n < pSignerInfo->UnauthAttrs.cAttr; n++) {
if (lstrcmpA(pSignerInfo->UnauthAttrs.rgAttr[n].pszObjId, szOID_RFC3161_counterSign) == 0) {
// Get size
r = CryptDecodeObject(PKCS_7_ASN_ENCODING, PKCS_CONTENT_INFO,
pSignerInfo->UnauthAttrs.rgAttr[n].rgValue[0].pbData,
pSignerInfo->UnauthAttrs.rgAttr[n].rgValue[0].cbData,
0, NULL, &dwSize);
if (!r) {
uprintf("PKI: Could not get CounterSigner (timestamp) data size: %s", WinPKIErrorString());
continue;
}
// Allocate memory.
pCounterSignerInfo = calloc(dwSize, 1);
if (pCounterSignerInfo == NULL) {
uprintf("PKI: Unable to allocate memory for CounterSigner (timestamp) data");
continue;
}
// Now read the CounterSigner message data
r = CryptDecodeObject(PKCS_7_ASN_ENCODING, PKCS_CONTENT_INFO,
pSignerInfo->UnauthAttrs.rgAttr[n].rgValue[0].pbData,
pSignerInfo->UnauthAttrs.rgAttr[n].rgValue[0].cbData,
0, (PVOID)pCounterSignerInfo, &dwSize);
if (!r) {
uprintf("PKI: Could not retrieve CounterSigner (timestamp) data: %s", WinPKIErrorString());
continue;
}
// Get the RFC 3161 timestamp message
timestamp_token = get_oid_data_from_asn1(pCounterSignerInfo->Content.pbData,
pCounterSignerInfo->Content.cbData, OID_RFC3161_timeStamp, sizeof(OID_RFC3161_timeStamp),
// 0x04 = "Octet String" ASN.1 tag
0x04, &timestamp_token_size);
if (timestamp_token) {
timestamp_str = get_oid_data_from_asn1(timestamp_token, timestamp_token_size, NULL, 0,
// 0x18 = "Generalized Time" ASN.1 tag
0x18, &timestamp_str_size);
if (timestamp_str) {
// As per RFC 3161 The syntax is: YYYYMMDDhhmmss[.s...]Z
if ((timestamp_str_size < 14) || (timestamp_str[timestamp_str_size - 1] != 'Z')) {
// Sanity checks
uprintf("PKI: Not an RFC 3161 timestamp");
DumpBufferHex(timestamp_str, timestamp_str_size);
} else {
ts = strtoull(timestamp_str, NULL, 10);
}
}
}
safe_free(pCounterSignerInfo);
}
}
return ts;
}
// Return the signature timestamp (as a YYYYMMDDHHMMSS value) or 0 on error
uint64_t GetSignatureTimeStamp(const char* path)
{
char *mpath = NULL;
BOOL r;
HMODULE hm;
HCERTSTORE hStore = NULL;
HCRYPTMSG hMsg = NULL;
DWORD dwSize, dwEncoding, dwContentType, dwFormatType;
PCMSG_SIGNER_INFO pSignerInfo = NULL;
DWORD dwSignerInfo = 0;
wchar_t *szFileName;
uint64_t timestamp = 0ULL;
// If the path is NULL, get the signature of the current runtime
if (path == NULL) {
szFileName = calloc(MAX_PATH, sizeof(wchar_t));
if (szFileName == NULL)
goto out;
hm = GetModuleHandle(NULL);
if (hm == NULL) {
uprintf("PKI: Could not get current executable handle: %s", WinPKIErrorString());
goto out;
}
dwSize = GetModuleFileNameW(hm, szFileName, MAX_PATH);
if ((dwSize == 0) || ((dwSize == MAX_PATH) && (GetLastError() == ERROR_INSUFFICIENT_BUFFER))) {
uprintf("PKI: Could not get module filename: %s", WinPKIErrorString());
goto out;
}
mpath = wchar_to_utf8(szFileName);
} else {
szFileName = utf8_to_wchar(path);
}
// Get message handle and store handle from the signed file.
r = CryptQueryObject(CERT_QUERY_OBJECT_FILE, szFileName,
CERT_QUERY_CONTENT_FLAG_PKCS7_SIGNED_EMBED, CERT_QUERY_FORMAT_FLAG_BINARY,
0, &dwEncoding, &dwContentType, &dwFormatType, &hStore, &hMsg, NULL);
if (!r) {
uprintf("PKI: Failed to get signature for '%s': %s", (path == NULL) ? mpath : path, WinPKIErrorString());
goto out;
}
// Get signer information size.
r = CryptMsgGetParam(hMsg, CMSG_SIGNER_INFO_PARAM, 0, NULL, &dwSignerInfo);
if (!r) {
uprintf("PKI: Failed to get signer size: %s", WinPKIErrorString());
goto out;
}
// Allocate memory for signer information.
pSignerInfo = (PCMSG_SIGNER_INFO)calloc(dwSignerInfo, 1);
if (!pSignerInfo) {
uprintf("PKI: Could not allocate memory for signer information");
goto out;
}
// Get Signer Information.
r = CryptMsgGetParam(hMsg, CMSG_SIGNER_INFO_PARAM, 0, (PVOID)pSignerInfo, &dwSignerInfo);
if (!r) {
uprintf("PKI: Failed to get signer information: %s", WinPKIErrorString());
goto out;
}
// Get the RFC 3161 timestamp
timestamp = GetRFC3161TimeStamp(pSignerInfo);
out:
safe_free(mpath);
safe_free(szFileName);
safe_free(pSignerInfo);
if (hStore != NULL)
CertCloseStore(hStore, 0);
if (hMsg != NULL)
CryptMsgClose(hMsg);
return timestamp;
}
// From https://msdn.microsoft.com/en-us/library/windows/desktop/aa382384.aspx
LONG ValidateSignature(HWND hDlg, const char* path)
{
@ -241,6 +389,7 @@ LONG ValidateSignature(HWND hDlg, const char* path)
{ 0xaac56b, 0xcd44, 0x11d0,{ 0x8c, 0xc2, 0x0, 0xc0, 0x4f, 0xc2, 0x95, 0xee } };
char *signature_name;
size_t i, len;
uint64_t current_ts, update_ts;
// Check the signature name. Make it specific enough (i.e. don't simply check for "Akeo")
// so that, besides hacking our server, it'll place an extra hurdle on any malicious entity
@ -292,6 +441,21 @@ LONG ValidateSignature(HWND hDlg, const char* path)
safe_free(trust_file.pcwszFilePath);
switch (r) {
case ERROR_SUCCESS:
// Verify that the timestamp of the downloaded update is in the future of our current one.
// This is done to prevent the use of an officially signed, but older binary, as potential attack vector.
current_ts = GetSignatureTimeStamp(NULL);
if (current_ts == 0ULL) {
uprintf("PKI: Cannot retreive the current binary's timestamp - Aborting update");
r = TRUST_E_TIME_STAMP;
} else {
update_ts = GetSignatureTimeStamp(path);
if (update_ts < current_ts) {
uprintf("PKI: Update timestamp (%" PRIi64 ") is older than ours (%" PRIi64 ")! - Aborting update", update_ts, current_ts);
r = TRUST_E_TIME_STAMP;
}
}
if (r != ERROR_SUCCESS)
MessageBoxExU(hDlg, lmprintf(MSG_300), lmprintf(MSG_299), MB_OK | MB_ICONERROR | MB_IS_RTL, selected_langid);
break;
case TRUST_E_NOSIGNATURE:
// Should already have been reported, but since we have a custom message for it...