CVE-2011-2516 in Shibboleth-sp
Summary
by MITRE
Off-by-one error in the XML signature feature in Apache XML Security for C++ 1.6.0, as used in Shibboleth before 2.4.3 and possibly other products, allows remote attackers to cause a denial of service (crash) via a signature using a large RSA key, which triggers a buffer overflow.
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Analysis
by VulDB Data Team • 12/28/2024
The vulnerability identified as CVE-2011-2516 represents a critical off-by-one error within the XML signature processing functionality of Apache XML Security for C++ version 1.6.0. This flaw specifically affects systems that utilize the Shibboleth identity federation software, where versions prior to 2.4.3 remain susceptible to exploitation. The vulnerability resides in the buffer management mechanisms that handle RSA key processing during XML signature validation operations, creating a condition where improper boundary checking leads to memory corruption.
The technical implementation of this vulnerability stems from inadequate bounds checking when processing large RSA keys within XML signatures. When a maliciously crafted XML document contains a signature with an excessively large RSA key, the system's buffer allocation logic fails to properly account for the key size, resulting in an off-by-one error that subsequently triggers a buffer overflow condition. This memory corruption occurs during the cryptographic validation process where the system attempts to parse and verify the signature parameters, particularly when handling RSA key sizes that exceed normal operational boundaries.
From an operational impact perspective, this vulnerability enables remote attackers to execute denial of service attacks against affected systems by simply submitting a specially crafted XML signature containing an oversized RSA key. The exploitation results in system crashes and process termination, effectively rendering the targeted service unavailable to legitimate users. The vulnerability's remote nature means that attackers do not require local system access or authentication credentials to exploit the flaw, making it particularly dangerous in web-facing applications that process XML signatures from untrusted sources.
The vulnerability aligns with CWE-129, which specifically addresses insufficient validation of length of input buffers, and demonstrates characteristics consistent with CWE-125, representing an out-of-bounds read condition. From an attack framework perspective, this vulnerability maps to the attack technique of resource exhaustion and system instability, which falls under the ATT&CK matrix category of Execution and Privilege Escalation. The flaw particularly affects systems implementing XML-based security protocols, making it relevant to web services, identity management systems, and any software that validates XML signatures using the affected Apache library.
Organizations should prioritize immediate patching of affected systems, upgrading to Shibboleth version 2.4.3 or later, which includes the necessary fixes for this buffer overflow condition. Additional mitigations include implementing input validation controls to restrict RSA key sizes in XML signatures, deploying network-based intrusion detection systems to monitor for suspicious XML traffic patterns, and establishing robust logging mechanisms to detect potential exploitation attempts. Security teams should also consider implementing application-level firewalls or API gateways that can filter out malformed XML signatures before they reach the vulnerable processing components, thereby reducing the attack surface and providing defense-in-depth protection against similar vulnerabilities.