iOS's SSL certificate parsing contains a flaw where it fails to check the basicConstraints parameter of certificates in the chain. By signing a new certificate using a legitimate end entity certificate, an attacker can obtain a "valid" certificate for any domain.
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Apple Security Advisory 2011-07-25-1 - A certificate chain validation issue existed in the handling of X.509 certificates. An attacker with a privileged network position may capture or modify data in sessions protected by SSL/TLS. Other attacks involving X.509 certificate validation may also be possible. This issue is addressed through improved validation of X.509 certificate chains. The iOS 4.3.5 software update addresses this issue.
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Apple Security Advisory 2011-07-25-2 - The iOS 4.2.10 software update addresses a certificate chain validation issue. The issue existed in the handling of X.509 certificates where an attacker with a privileged network position may capture or modify data in sessions protected by SSL/TLS. Other attacks involving X.509 certificate validation may also be possible. This issue is addressed through improved validation of X.509 certificate chains.
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