CVE-2009-1387 in OpenSSL
Summary
by MITRE
The dtls1_retrieve_buffered_fragment function in ssl/d1_both.c in OpenSSL before 1.0.0 Beta 2 allows remote attackers to cause a denial of service (NULL pointer dereference and daemon crash) via an out-of-sequence DTLS handshake message, related to a "fragment bug."
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Analysis
by VulDB Data Team • 09/06/2019
The vulnerability described in CVE-2009-1387 represents a critical denial of service flaw within the OpenSSL implementation of the Datagram Transport Layer Security protocol. This issue affects versions of OpenSSL prior to 1.0.0 Beta 2 and specifically targets the dtls1_retrieve_buffered_fragment function located in the ssl/d1_both.c source file. The flaw manifests when the DTLS handshake process receives out-of-sequence messages, creating a condition where the software fails to properly handle fragmented handshake data.
The technical nature of this vulnerability stems from a NULL pointer dereference error that occurs during the processing of DTLS handshake fragments. When an attacker sends malformed or out-of-order DTLS handshake messages, the function attempts to access a NULL pointer reference, leading to an immediate crash of the OpenSSL daemon. This behavior directly aligns with CWE-476, which categorizes NULL pointer dereference as a common weakness that can result in application termination and system instability. The vulnerability exploits the lack of proper input validation and error handling within the DTLS fragment buffering mechanism.
The operational impact of this vulnerability extends beyond simple service disruption, as it can be exploited by remote attackers without requiring authentication or privileged access. The daemon crash resulting from this flaw can be leveraged to create sustained denial of service conditions against systems running vulnerable OpenSSL implementations. This type of attack falls under the ATT&CK technique T1499.004, which covers network denial of service attacks. The vulnerability particularly affects services that rely on DTLS for secure communication, including VoIP systems, IoT devices, and any network infrastructure that utilizes OpenSSL for secure datagram transmission.
Mitigation strategies for this vulnerability require immediate patching of affected OpenSSL installations to versions 1.0.0 Beta 2 or later, where the fragment handling logic has been corrected. Organizations should also implement network-level monitoring to detect unusual DTLS handshake patterns that may indicate exploitation attempts. Additional defensive measures include configuring firewalls to limit DTLS traffic and implementing rate limiting mechanisms to prevent flood-based exploitation attempts. The fix implemented in subsequent OpenSSL versions addresses the core issue by adding proper NULL pointer checks and robust error handling within the fragment retrieval process, ensuring that out-of-sequence messages do not cause daemon termination. This vulnerability serves as a reminder of the critical importance of proper input validation in cryptographic implementations and demonstrates how seemingly minor flaws in protocol handling can result in significant system instability and availability issues.