Trustwave's SpiderLabs Security Advisory TWSL2011-007:
iOS SSL Implementation Does Not Validate Certificate Chain

https://www.trustwave.com/spiderlabs/advisories/TWSL2011-007.txt

Published: 2011-07-25
Version: 1.0

Vendor: Apple (http://www.apple.com)
Product: iOS
Version affected:  Versions Prior to 5.0b4, 4.3.5, and 4.2.10

Product description:
iOS is Apple's mobile operating system for the iPhone, iPod Touch, and iPad
hardware platforms.

Credit: Paul Kehrer of Trustwave

Finding: iOS SSL Implementation Does Not Validate Certificate Chain
CVE: CVE-2011-0228

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. For example:

-TrustedCA
--somedomain.com (legitimate certificate)
---api.someotherdomain.com (signed by somedomain.com)

Using this technique any SSL traffic using the api.someotherdomain.com
certificate can be intercepted and decrypted by the issuer. No notification
of the invalid nature of the certificate is presented to the iOS user.
This method allows for transparent man-in-the-middle attacks against
encrypted iOS communications.


Remediation Steps:
Users should update to the latest version of iOS in order to address this
issue. This vulnerability has been corrected in versions 5.0b4, 4.3.5, and
4.2.10.

Revision History:
07/15/11 - Vulnerability Disclosed
07/25/11 - Patch Released
07/25/11 - Advisory Published

References:
1. http://support.apple.com/kb/HT4824
2. http://support.apple.com/kb/HT4825


About Trustwave:
Trustwave is the leading provider of on-demand and subscription-based
information security and payment card industry compliance management
solutions to businesses and government entities throughout the world. For
organizations faced with today's challenging data security and compliance
environment, Trustwave provides a unique approach with comprehensive
solutions that include its flagship TrustKeeper compliance management
software and other proprietary security solutions. Trustwave has helped
thousands of organizations--ranging from Fortune 500 businesses and large
financial institutions to small and medium-sized retailers--manage
compliance and secure their network infrastructure, data communications and
critical information assets. Trustwave is headquartered in Chicago with
offices throughout North America, South America, Europe, Africa, China and
Australia. For more information, visit https://www.trustwave.com

About Trustwave's SpiderLabs:
SpiderLabs(R) is the advanced security team at Trustwave focused on
application security, incident response, penetration testing, physical
security and security research. The team has performed over a thousand
incident investigations, thousands of penetration tests and hundreds of
application security tests globally. In addition, the SpiderLabs Research
team provides intelligence through bleeding-edge research and proof of
concept tool development to enhance Trustwave's products and services.
https://www.trustwave.com/spiderlabs

Disclaimer:
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warranty of any kind. Trustwave disclaims all warranties, either express or
implied, including the warranties of merchantability and fitness for a
particular purpose. In no event shall Trustwave or its suppliers be liable
for any damages whatsoever including direct, indirect, incidental,
consequential, loss of business profits or special damages, even if
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apply.





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