CVE-2017-3206 in Flamingo amf-serializer
Summary
by MITRE
The Java implementation of AMF3 deserializers used by Flamingo amf-serializer by Exadel, version 2.2.0, allows external entity references (XXEs) from XML documents embedded within AMF3 messages. If the XML parsing is handled incorrectly it could potentially expose sensitive data on the server, denial of service, or server side request forgery.
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Analysis
by VulDB Data Team • 12/26/2024
The vulnerability identified as CVE-2017-3206 resides within the Java implementation of AMF3 deserializers utilized by Flamingo amf-serializer version 2.2.0 developed by Exadel. This flaw represents a critical security weakness that stems from improper handling of XML documents embedded within AMF3 messages, creating a pathway for external entity reference attacks. The AMF3 format is commonly used for serializing and deserializing data in Adobe Flash applications and related systems, making this vulnerability particularly concerning for applications that process untrusted AMF3 input from remote sources.
The technical implementation of this vulnerability occurs when the AMF3 deserializer processes XML content without proper sanitization or validation of external entity declarations. When XML documents are embedded within AMF3 messages and subsequently parsed by the vulnerable deserializer, the system fails to adequately restrict external entity references that could be maliciously constructed. This parsing behavior directly violates security principles outlined in CWE-611, which addresses improper restriction of XML external entity reference vulnerabilities. The flaw essentially allows attackers to construct malicious AMF3 messages containing specially crafted XML that references external resources, potentially enabling data exfiltration, denial of service conditions, or server-side request forgery attacks.
The operational impact of this vulnerability extends beyond simple data exposure, as it can enable attackers to perform sophisticated attacks against systems that process AMF3 input. When an application accepts AMF3 messages from untrusted sources and uses the vulnerable Flamingo serializer, an attacker can exploit the XXE vulnerability to access internal network resources, read local files on the server, or initiate requests to internal services. This capability aligns with ATT&CK technique T1071.004 for application layer protocol tunneling and T1046 for network service scanning. The vulnerability particularly affects systems where AMF3 deserialization occurs in server-side applications that handle user input or external data feeds, creating potential attack vectors for privilege escalation or lateral movement within network environments.
Mitigation strategies for CVE-2017-3206 should focus on immediate patching of the Flamingo amf-serializer component to version 2.2.1 or later, which contains fixes for the XXE vulnerability. Organizations should also implement strict input validation and sanitization for all AMF3 messages, particularly those containing embedded XML content. Network segmentation and firewall rules can help limit access to systems that process AMF3 data, reducing the attack surface. Additionally, implementing proper XML parser configurations that disable external entity resolution and DTD processing will prevent similar vulnerabilities in other components. Security monitoring should be enhanced to detect unusual patterns in AMF3 message processing that might indicate exploitation attempts, while regular security assessments should verify that no other components within the application stack are similarly vulnerable to XXE attacks. The vulnerability demonstrates the importance of proper input validation and secure coding practices, particularly when dealing with complex serialization formats that may contain nested data structures requiring careful parsing and validation.