TWSL2011-007: iOS SSL Implementation Does Not Validate Certificate- Chain

From: Trustwave Advisories <>
Subject: TWSL2011-007: iOS SSL Implementation Does Not Validate Certificate- Chain

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

Published: 2011-07-25
Version: 1.0

Vendor: Apple (
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 (legitimate certificate) (signed by

Using this technique any SSL traffic using the
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

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


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About Trustwave's SpiderLabs:
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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.

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