CVE-2016-10397 in PHP
Summary
by MITRE
In PHP before 5.6.28 and 7.x before 7.0.13, incorrect handling of various URI components in the URL parser could be used by attackers to bypass hostname-specific URL checks, as demonstrated by evil.example.com:80#@good.example.com/ and evil.example.com:[email protected]/ inputs to the parse_url function (implemented in the php_url_parse_ex function in ext/standard/url.c).
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Analysis
by VulDB Data Team • 12/12/2022
This vulnerability resides in the PHP URL parsing functionality where improper handling of URI components creates a security bypass mechanism. The flaw specifically affects PHP versions prior to 5.6.28 and 7.0.13, impacting the parse_url function implementation within the ext/standard/url.c file. The vulnerability stems from how the URL parser processes special characters and components such as the hash symbol # and question mark ? in conjunction with hostname specifications. Attackers can exploit this by crafting malicious URLs that appear to originate from a trusted domain while actually containing embedded components that redirect the parsing logic. The malicious inputs demonstrate how evil.example.com:80#good.example.com/ and evil.example.com:80?good.example.com/ can manipulate the URL parsing behavior to bypass hostname validation checks that are commonly used for security purposes.
The technical execution of this vulnerability relies on the improper interpretation of URL components by the php_url_parse_ex function. When processing URLs with embedded hash characters or query parameters, the parser fails to correctly isolate the hostname component, allowing attackers to inject malicious content that can circumvent security controls. This represents a classic case of improper input validation where the application's URL parsing logic does not properly sanitize or validate the structure of URLs before processing them. The vulnerability can be categorized under CWE-20 as "Improper Input Validation" and specifically relates to CWE-770 as "Allocation of Resources Without Limits or Throttling" since the malformed URL processing could potentially lead to resource exhaustion or unexpected behavior in applications that rely on proper URL parsing.
The operational impact of this vulnerability extends beyond simple URL parsing issues to potentially enable various attack vectors including but not limited to open redirect attacks, insecure direct object references, and host header injection scenarios. Applications that perform hostname validation for security purposes may be bypassed entirely, allowing attackers to redirect users to malicious sites or access restricted resources. This vulnerability aligns with ATT&CK technique T1190 "Exploit Public-Facing Application" and can be leveraged to bypass web application firewalls, content security policies, and other host-based security controls that rely on proper URL parsing for validation. The vulnerability is particularly dangerous in environments where applications perform access control based on URL hostname components, as it allows attackers to craft URLs that appear legitimate while containing embedded malicious components.
Mitigation strategies for this vulnerability require immediate patching of affected PHP versions to either 5.6.28 or 7.0.13 or later releases. Organizations should also implement additional input validation layers in their applications to sanitize URL inputs before passing them to PHP's parse_url function. Security monitoring should include detection of unusual URL patterns that contain embedded special characters or malformed components. The vulnerability demonstrates the importance of proper URI parsing implementation and highlights the need for comprehensive testing of URL handling functions in web applications. Additional defensive measures include implementing strict URL validation rules, using allowlists for trusted domains, and deploying web application firewalls that can detect and block malformed URL patterns. Organizations should also conduct regular security assessments to identify similar vulnerabilities in other components of their web applications that may be susceptible to similar parsing flaws.