CVE-2012-0845 in Mac OS X
Summary
by MITRE
SimpleXMLRPCServer.py in SimpleXMLRPCServer in Python before 2.6.8, 2.7.x before 2.7.3, 3.x before 3.1.5, and 3.2.x before 3.2.3 allows remote attackers to cause a denial of service (infinite loop and CPU consumption) via an XML-RPC POST request that contains a smaller amount of data than specified by the Content-Length header.
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Analysis
by VulDB Data Team • 06/01/2021
The vulnerability identified as CVE-2012-0845 represents a critical denial of service flaw within Python's SimpleXMLRPCServer implementation that affects multiple Python versions including 2.6.8, 2.7.3, 3.1.5, and 3.2.3. This vulnerability stems from a fundamental mismatch between the Content-Length header value and the actual data payload in XML-RPC POST requests, creating a condition where the server enters an infinite loop during data processing. The flaw specifically impacts the server's ability to handle malformed requests properly, leading to excessive CPU consumption and potential system resource exhaustion.
The technical implementation of this vulnerability occurs when the SimpleXMLRPCServer receives an XML-RPC request where the Content-Length header indicates a larger data payload than what is actually transmitted. The server's parsing mechanism attempts to read the specified number of bytes from the request stream, but when fewer bytes are available, it enters a loop attempting to fulfill the requested read operation. This behavior manifests as continuous CPU utilization and can be exploited by remote attackers to perform sustained denial of service attacks against vulnerable Python applications. The vulnerability is categorized under CWE-129 as an improper validation of the length of a buffer, specifically failing to validate that the data received matches the expected length specified in HTTP headers.
From an operational standpoint, this vulnerability poses significant risks to web applications and services that rely on Python's XML-RPC functionality for remote procedure calls. Attackers can exploit this weakness by crafting malicious XML-RPC requests that specify a large Content-Length value while sending only minimal data, causing the server to consume excessive processing cycles. The impact extends beyond simple service disruption as the infinite loop can potentially exhaust system resources, affecting other services running on the same server and potentially leading to complete system unavailability. This vulnerability aligns with ATT&CK technique T1499.004 for network denial of service attacks, where adversaries leverage protocol-level flaws to exhaust system resources.
The mitigation strategy for CVE-2012-0845 requires immediate patching of affected Python versions to the corrected releases that properly validate Content-Length headers against actual data received. Organizations should also implement request size limiting mechanisms at network level firewalls or reverse proxies to prevent malformed requests from reaching vulnerable Python applications. Additionally, monitoring systems should be configured to detect unusual CPU utilization patterns that may indicate exploitation attempts. Security teams should conduct comprehensive vulnerability assessments to identify all systems running affected Python versions and ensure proper patch management processes are in place to prevent similar issues in the future. The vulnerability demonstrates the importance of proper input validation and buffer length checking in preventing resource exhaustion attacks that can be leveraged for broader system compromise.