Date: Fri, 21 Oct 2011 14:03:07 +0200 From: Florian Weimer <fw@...eb.enyo.de> To: oss-security@...ts.openwall.com Subject: Re: PR attack against XML Encryption * Yves-Alexis Perez: > On jeu., 2011-10-20 at 12:58 +0200, Florian Weimer wrote: >> A German university has released a press release, alleging a >> vulnerability in the W3C XML Encryption standard. Apparently, error >> reporting from existing implementations can be used as an oracle to >> recover information from messages encrypted in CBC mode. >> >> Details have not been published, as far as I know. Does anybody know >> more? > but afaict the paper is not (yet?) available freely. I took a brief look at the paper, and it's basically rehashing older work on decryption error oracles. Full message recovery is apparently possible, but leaves traces in the server log. It's the standard which is at fault: encryption without authentication is just not safe in general. IBM has already changed error reporting in response to this issue: <http://www-01.ibm.com/support/docview.wss?uid=swg1IC76651> Of course, without an application-independent way to check the integrity of the decrypted message (which would be provided by a combiend encryption/authentication mode), this is only a partial solution. The authors also mention a second issue, where implementations confuse signed and encrypted parts of a SOAP message, allowing attackers to inject unsigned data which is presented as signed to the application. This probably needs a separate fix.
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