XML Signature Exclusion

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Attack description

In the absence of an XML Signature, the signature verification component did not monitor any XML Signature at all, but nevertheless treated the message as validly signed. The task of user identification and authorization took place in other components relying solely on the X.509 certificate data from the BinarySecurityToken el- ement, which can be present even if there is no signature. Hence, that SOAP request message was authorized to trigger operations on behalf of the owner of the X.509 certificate. For completeness, the message is depicted in Figure 3.5. To conclude, while performing an arbitrary SOAP request for any of the EC2 SOAP interface operations, an attacker needs only the public X.509 certificate of the victim. Since X.509 certificates are by definition considered to constitute public data, harvesting them from the Internet is not a major challenge for an attacker.

Attack subtypes

There are no attack subtypes for this attack.

Prerequisites for attack

In order to execute the attack, there are the following prerequisites:

  1. Attacker knows endpoint of web service. otherwise he is not able to reach the web service.
  2. Attacker can reach endpoint from its location.
  3. Attacker is in possession of a validly signed XML message or he is in possession of a valid public certificate and can construct a valid message with a missing XML Signature.

Graphical representation of attack

AttackedComponent Signature.png

  • Red = attacked web service component
  • Black = location of attacker
  • Blue = web service component not directly involved in attack.

Attack example

Practical attacks were shown by Somorovsky et al.[1], who showed how to attack cloud interfaces of Amazon and Eucalyptus cloud providers. This enabled them to execute arbitrary methods on cloud interfaces.

Attack mitigation / countermeasures

Attack categorisation

Categorisation by violated security objective

Categorisation by number of involved parties

Categorisation by attacked component in web service architecture

Categorisation by attack spreading


  1. Juraj So­mo­rovs­ky, Mario Hei­de­rich, Meiko Jen­sen, Jörg Schwenk, Nils Grusch­ka, Luigi Lo Ia­co­no. All Your Clouds are Be­long to us – Se­cu­ri­ty Ana­ly­sis of Cloud Ma­nage­ment In­ter­faces. In Pro­cee­dings of the ACM Cloud Com­pu­ting Se­cu­ri­ty Work­shop (CCSW), 2011. https://www.nds.rub.de/research/publications/amazon-hacking/
  2. Juraj Somorovsky. On the In­se­cu­ri­ty of XML Se­cu­ri­ty. PhD thesis supervised by Jörg Schwenk and Kenny Paterson, Ruhr University Bochum. https://www.nds.rub.de/research/publications/xmlinsecurity/