CVE-2012-6431 in Symfony
Summary
by MITRE
Symfony 2.0.x before 2.0.20 does not process URL encoded data consistently within the Routing and Security components, which allows remote attackers to bypass intended URI restrictions via a doubly encoded string.
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Analysis
by VulDB Data Team • 12/21/2021
The vulnerability identified as CVE-2012-6431 affects Symfony 2.0.x versions prior to 2.0.20 and represents a critical inconsistency in how the framework handles URL encoded data within its Routing and Security components. This flaw stems from the improper processing of doubly encoded strings, which creates a pathway for malicious actors to bypass intended URI restrictions and gain unauthorized access to restricted resources. The issue manifests when the framework fails to consistently decode URL encoded data, allowing attackers to craft payloads that exploit this inconsistency to circumvent security controls.
The technical root cause of this vulnerability lies in the inconsistent handling of URL decoding operations within Symfony's core components. When a URL contains doubly encoded sequences such as %252F instead of %2F, the routing component may process these differently than the security component, creating a discrepancy that attackers can leverage. This inconsistency enables a form of bypass attack where an attacker can submit a URI that appears to be properly encoded but contains embedded encoded sequences that are processed differently by various parts of the framework. The vulnerability operates at the intersection of web application security and input validation, where the framework's inconsistent behavior creates a security gap that can be exploited to access restricted paths or resources.
The operational impact of this vulnerability extends beyond simple access control bypasses, as it can potentially enable attackers to traverse directory structures, access protected endpoints, or exploit other security mechanisms within the application. Attackers can craft malicious requests using doubly encoded strings that will be properly decoded by one component but remain encoded or processed differently by another, allowing them to access resources that should be restricted. This vulnerability particularly affects applications that rely heavily on Symfony's routing and security features, potentially leading to unauthorized data access, privilege escalation, or complete system compromise depending on the application's configuration and the resources being protected.
Organizations affected by this vulnerability should immediately upgrade to Symfony 2.0.20 or later versions where the inconsistency in URL decoding has been resolved. The fix implemented in the patched versions ensures consistent processing of URL encoded data across all framework components, eliminating the possibility of attackers exploiting the discrepancy between routing and security processing. Additionally, application developers should review their code for potential reliance on URL encoding behaviors that might be affected by this fix, and ensure proper input validation is implemented at multiple layers of the application architecture. This vulnerability aligns with CWE-129 and CWE-20, representing issues in input validation and improper handling of encoded data, and can be categorized under the ATT&CK technique T1078 for Valid Accounts and T1566 for Phishing, as attackers may use such bypasses to escalate privileges or gain unauthorized access to sensitive resources.