Category: Software Development

Vulnerability in .NET SignedXml

.NET’s SignedXML class has had a risky implementation for lookup of XML elements by id in GetIdElement() when resolving signed xml references. The lookup validated only the first element if there are several with the same id. This opens up for XML Signature Wrapping attacks in any library that is using the default implementation without… Continue reading Vulnerability in .NET SignedXml

XML Signatures and References

Last week I showed a peculiar XML Signature that validates even though the containing document was changed. The reason is that the signature lacks References. Before explaining what’s wrong with the signature – and with the validation code, we’ll have a look at how XML Signatures work. XML DSig Primer XML in general is a… Continue reading XML Signatures and References

An Always Valid XML Signature

XML Signatures are powerful, but also a bit tricky to get right. Here’s a challenge: I have a signature that will validate, even though the contents of the XML document are altered. This is the “magic” signature that validates regardless of what XML document it is placed in. <Signature xmlns="http://www.w3.org/2000/09/xmldsig#"> <SignedInfo> <CanonicalizationMethod Algorithm="http://www.w3.org/TR/2001/REC-xml-c14n-20010315" /> <SignatureMethod… Continue reading An Always Valid XML Signature