Whitepaper: Command Injection in XML Digital Signatures and Encryption
iSEC Partners and Brad Hill are pleased to announce the availability of a new
whitepaper describing design flaws and new attacks against the XML Digital
Signature and XML Encryption standards. It accompanies recent advisories and
provides detailed guidance for auditors and implementers of these products.
Full Paper Available at:
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http://www.isecpartners.com/files/XMLDSIG_Command_Injection.pdf
Abstract:
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The XML Digital Signature (XMLDSIG) and XML Encryption (XMLENC) standards are
complex protocols for securing XML and other content. Among its complexities,
the XMLDSIG standard specifies various ?Transform? algorithms to identify,
manipulate and canonicalize signed content and key material. Unfortunately, the
defined transforms have not been rigorously constrained to prevent their use as
attack vectors, and denial of service or even arbitrary code execution are
probable in implementations that have not specifically guarded against such
risks.
Attacks against the processing application can be embedded in the KeyInfo
portion of a signature, making them inherently unauthenticated, or in the
SignedInfo block. Although tampering with the SignedInfo should be detectable,
a defective implied order of operations in the specification may still allow
unauthenticated attacks here.
The ability to execute arbitrary code and perform file system operations with a
malicious, invalid signature has been confirmed by the researcher in at least
two independent XMLDSIG implementations, and other implementations may be
similarly vulnerable. This paper describes the vulnerabilities in detail and
offers advice for remediation. The most damaging attack is also likely to apply
in other contexts where XSLT is accepted as input, and should be considered by
all implementers of complex XML processing systems.
About iSEC Partners:
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iSEC Partners is a full-service security consulting firm that provides
penetration testing, secure systems development, security education
and software design verification.
115 Sansome Street, Suite 1005
San Francisco, CA 94104
Phone: (415) 217-0052