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Security fix for CVE-2009-0217

svn path=/branches/mono-1-1-7/mcs/; revision=137892
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commit 939994df00fc3e1372b9dc1243e261e2f6c6c133 1 parent ed260f1
Sebastien Pouliot authored
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31 mcs/class/System.Security/System.Security.Cryptography.Xml/SignedXml.cs
@@ -571,17 +571,28 @@ public bool CheckSignature (KeyedHashAlgorithm macAlg)
return false;
byte[] actual = macAlg.ComputeHash (s);
- // HMAC signature may be partial
+ // HMAC signature may be partial and specified by <HMACOutputLength>
if (m_signature.SignedInfo.SignatureLength != null) {
- int length = actual.Length;
- try {
- // SignatureLength is in bits
- length = (Int32.Parse (m_signature.SignedInfo.SignatureLength) >> 3);
- }
- catch {
- }
-
- if (length != actual.Length) {
+ int length = Int32.Parse (m_signature.SignedInfo.SignatureLength);
+ // we only support signatures with a multiple of 8 bits
+ // and the value must match the signature length
+ if ((length & 7) != 0)
+ throw new CryptographicException ("Signature length must be a multiple of 8 bits.");
+
+ // SignatureLength is in bits (and we works on bytes, only in multiple of 8 bits)
+ // and both values must match for a signature to be valid
+ length >>= 3;
+ if (length != m_signature.SignatureValue.Length)
+ throw new CryptographicException ("Invalid signature length.");
+
+ // is the length "big" enough to make the signature meaningful ?
+ // we use a minimum of 80 bits (10 bytes) or half the HMAC normal output length
+ // e.g. HMACMD5 output 128 bits but our minimum is 80 bits (not 64 bits)
+ int minimum = Math.Max (10, actual.Length / 2);
+ if (length < minimum)
+ throw new CryptographicException ("HMAC signature is too small");
+
+ if (length < actual.Length) {
byte[] trunked = new byte [length];
Buffer.BlockCopy (actual, 0, trunked, 0, length);
actual = trunked;
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