Fix for CMS/PKCS7 MMA. If RSA decryption fails use a random key and

continue with symmetric decryption process to avoid leaking timing
information to an attacker.

Thanks to Ivan Nestlerode <inestlerode@us.ibm.com> for discovering
this issue. (CVE-2012-0884)

1 files changed, 33 insertions, 4 deletions

diff --git a/crypto/cms/cms_smime.c b/crypto/cms/cms_smime.c
index a40307605b..8c56e3a852 100644
--- a/crypto/cms/cms_smime.c
+++ b/crypto/cms/cms_smime.c
@@ -611,7 +611,10 @@ int CMS_decrypt_set1_pkey(CMS_ContentInfo *cms, EVP_PKEY *pk, X509 *cert)
 	STACK_OF(CMS_RecipientInfo) *ris;
 	CMS_RecipientInfo *ri;
 	int i, r;
+	int debug = 0;
 	ris = CMS_get0_RecipientInfos(cms);
+	if (ris)
+		debug = cms->d.envelopedData->encryptedContentInfo->debug;
 	for (i = 0; i < sk_CMS_RecipientInfo_num(ris); i++)
 		{
 		ri = sk_CMS_RecipientInfo_value(ris, i);
@@ -625,17 +628,38 @@ int CMS_decrypt_set1_pkey(CMS_ContentInfo *cms, EVP_PKEY *pk, X509 *cert)
 			CMS_RecipientInfo_set0_pkey(ri, pk);
 			r = CMS_RecipientInfo_decrypt(cms, ri);
 			CMS_RecipientInfo_set0_pkey(ri, NULL);
-			if (r > 0)
-				return 1;
 			if (cert)
 				{
+				/* If not debugging clear any error and
+				 * return success to avoid leaking of
+				 * information useful to MMA
+				 */
+				if (!debug)
+					{
+					ERR_clear_error();
+					return 1;
+					}
+				if (r > 0)
+					return 1;
 				CMSerr(CMS_F_CMS_DECRYPT_SET1_PKEY,
 						CMS_R_DECRYPT_ERROR);
 				return 0;
 				}
-			ERR_clear_error();
+			/* If no cert and not debugging don't leave loop
+			 * after first successful decrypt. Always attempt
+			 * to decrypt all recipients to avoid leaking timing
+			 * of a successful decrypt.
+			 */
+			else if (r > 0 && debug)
+				return 1;
 			}
 		}
+	/* If no cert and not debugging always return success */
+	if (!cert && !debug)
+		{
+		ERR_clear_error();
+		return 1;
+		}
 
 	CMSerr(CMS_F_CMS_DECRYPT_SET1_PKEY, CMS_R_NO_MATCHING_RECIPIENT);
 	return 0;
@@ -718,9 +742,14 @@ int CMS_decrypt(CMS_ContentInfo *cms, EVP_PKEY *pk, X509 *cert,
 		}
 	if (!dcont && !check_content(cms))
 		return 0;
+	if (flags & CMS_DEBUG_DECRYPT)
+		cms->d.envelopedData->encryptedContentInfo->debug = 1;
+	else
+		cms->d.envelopedData->encryptedContentInfo->debug = 0;
+	if (!pk && !cert && !dcont && !out)
+		return 1;
 	if (pk && !CMS_decrypt_set1_pkey(cms, pk, cert))
 		return 0;
-
 	cont = CMS_dataInit(cms, dcont);
 	if (!cont)
 		return 0;