Add additional validations based on X.690 rules

The library was a tad bit fast and loose with respect to parsing some of the ASN.1 presented to it. It was kind of like we used Alternate Encoding Rules (AER), which was more relaxed than BER, CER or DER. This commit closes most of the gaps.

The changes are distantly related to Issue 346. Issue 346 caught a CVE bcause of the transient DoS. These fixes did not surface with negative effcts. Rather, the library was a bit too accomodating to the point it was not conforming

1 files changed, 6 insertions, 5 deletions

diff --git a/asn.cpp b/asn.cpp
index 2e923ef7..79b4cbc3 100644
--- a/asn.cpp
+++ b/asn.cpp
@@ -123,7 +123,7 @@ size_t BERDecodeOctetString(BufferedTransformation &bt, SecByteBlock &str)
 	size_t bc;

 	if (!BERLengthDecode(bt, bc))

 		BERDecodeError();

-	if (bc > bt.MaxRetrievable())

+	if (bc > bt.MaxRetrievable()) // Issue 346

 		BERDecodeError();

 

 	str.New(bc);

@@ -141,7 +141,7 @@ size_t BERDecodeOctetString(BufferedTransformation &bt, BufferedTransformation &
 	size_t bc;

 	if (!BERLengthDecode(bt, bc))

 		BERDecodeError();

-	if (bc > bt.MaxRetrievable())

+	if (bc > bt.MaxRetrievable()) // Issue 346

 		BERDecodeError();

 

 	bt.TransferTo(str, bc);

@@ -165,7 +165,7 @@ size_t BERDecodeTextString(BufferedTransformation &bt, std::string &str, byte as
 	size_t bc;

 	if (!BERLengthDecode(bt, bc))

 		BERDecodeError();

-	if (bc > bt.MaxRetrievable())

+	if (bc > bt.MaxRetrievable()) // Issue 346

 		BERDecodeError();

 

 	SecByteBlock temp(bc);

@@ -196,11 +196,12 @@ size_t BERDecodeBitString(BufferedTransformation &bt, SecByteBlock &str, unsigne
 		BERDecodeError();

 	if (bc == 0)

 		BERDecodeError();

-	if (bc > bt.MaxRetrievable())

+	if (bc > bt.MaxRetrievable()) // Issue 346

 		BERDecodeError();

 

+	// X.690, 8.6.2.2: "The number [of unused bits] shall be in the range zero to seven"

 	byte unused;

-	if (!bt.Get(unused))

+	if (!bt.Get(unused) || unused > 7)

 		BERDecodeError();

 	unusedBits = unused;

 	str.resize(bc-1);