CVE-2015-1269 in Chrome
Summary
by MITRE
The DecodeHSTSPreloadRaw function in net/http/transport_security_state.cc in Google Chrome before 43.0.2357.130 does not properly canonicalize DNS hostnames before making comparisons to HSTS or HPKP preload entries, which allows remote attackers to bypass intended access restrictions via a string that (1) ends in a . (dot) character or (2) is not entirely lowercase.
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Analysis
by VulDB Data Team • 05/21/2022
The vulnerability identified as CVE-2015-1269 represents a critical security flaw in Google Chrome's handling of HTTP Strict Transport Security and HTTP Public Key Pinning preload lists. This issue resides within the DecodeHSTSPreloadRaw function located in net/http/transport_security_state.cc, where the browser fails to properly canonicalize DNS hostnames before performing comparisons against preloaded security entries. The improper canonicalization process creates a pathway for attackers to bypass intended access restrictions by exploiting the inconsistent handling of hostname representations during security policy validation. The flaw specifically manifests when hostnames contain trailing dot characters or mixed case lettering, which should be normalized according to standard DNS canonicalization practices but are not properly processed by Chrome's security implementation.
The technical exploitation of this vulnerability leverages the fundamental difference between how DNS hostnames are canonically represented versus how Chrome processes them for security policy enforcement. When a hostname ends with a dot character or contains non-lowercase letters, the function fails to normalize these variations before comparing them against preloaded HSTS or HPKP entries. This normalization failure allows attackers to craft malicious hostnames that appear different to the browser's security mechanisms but are functionally equivalent to legitimate preloaded entries. The vulnerability essentially creates a bypass mechanism where an attacker can submit a hostname with trailing dots or mixed case formatting that would match against a preloaded security entry, thereby circumventing the intended security protections. This represents a classic case of improper input validation and canonicalization, which aligns with CWE-180, "Improper Input Validation," and CWE-182, "Collapse of Data into Smaller Representation."
From an operational impact perspective, this vulnerability significantly undermines the effectiveness of Chrome's security infrastructure by allowing attackers to bypass critical transport security mechanisms. The ability to bypass HSTS preload entries means that users could be redirected to insecure HTTP connections even when the browser has preloaded security policies to enforce HTTPS. Similarly, bypassing HPKP preload entries removes the protection against certificate pinning enforcement, potentially allowing man-in-the-middle attacks to succeed against sites that should be protected by public key pinning. The vulnerability affects all Chrome versions prior to 43.0.2357.130, representing a substantial attack surface where users were exposed to downgrade attacks and certificate validation bypasses. This issue directly impacts the trust model of web browsers and can lead to data interception, session hijacking, and other credential theft attacks that rely on breaking the secure transport layer.
The mitigation strategy for this vulnerability involves upgrading to Chrome version 43.0.2357.130 or later, where the canonicalization process has been properly implemented to normalize DNS hostnames before security policy comparisons. Organizations should also implement network monitoring to detect potential exploitation attempts and ensure that their browser deployment policies include regular updates to maintain security. Security teams should review their web application security configurations to ensure that applications are not relying on potentially vulnerable browser behaviors. Additionally, the vulnerability highlights the importance of proper canonicalization in security-critical code paths and demonstrates how seemingly minor implementation details in security functions can have significant operational consequences. This issue aligns with ATT&CK technique T1071.004, "Application Layer Protocol: DNS," and T1566, "Phishing," as attackers could exploit this vulnerability to bypass security protections and conduct more effective phishing attacks. The remediation process should include comprehensive testing of security policy enforcement mechanisms to ensure that hostname normalization occurs correctly across all security-critical functions within the browser's transport security implementation.