CVE-2008-1949 in gnutls
Summary
by MITRE
The _gnutls_recv_client_kx_message function in lib/gnutls_kx.c in libgnutls in gnutls-serv in GnuTLS before 2.2.4 continues to process Client Hello messages within a TLS message after one has already been processed, which allows remote attackers to cause a denial of service (NULL dereference and crash) via a TLS message containing multiple Client Hello messages, aka GNUTLS-SA-2008-1-2.
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Analysis
by VulDB Data Team • 12/30/2024
The vulnerability described in CVE-2008-1949 represents a critical denial of service flaw within the GnuTLS library implementation that affects the secure communication protocols used by numerous network applications. This issue specifically impacts the gnutls-serv component of GnuTLS versions prior to 2.2.4, where the library fails to properly validate the sequence of TLS handshake messages. The flaw occurs in the _gnutls_recv_client_kx_message function located in lib/gnutls_kx.c, which demonstrates a fundamental failure in state management during the TLS handshake process. When a malicious client sends a TLS message containing multiple Client Hello messages, the vulnerable implementation continues processing subsequent Client Hello messages even after having already handled one, creating an exploitable condition that leads to system instability.
The technical nature of this vulnerability stems from improper message handling and state validation within the TLS protocol implementation. During the TLS handshake, the Client Hello message serves as the initial negotiation step where the client communicates its supported cryptographic parameters to the server. The gnutls-serv implementation incorrectly processes multiple Client Hello messages within a single TLS message, leading to a scenario where the system attempts to dereference a NULL pointer during the key exchange phase. This NULL dereference results in an immediate crash of the targeted service, effectively rendering it unavailable to legitimate users. The vulnerability operates at the protocol level rather than at the application layer, making it particularly dangerous as it can affect any service relying on GnuTLS for secure communications, including web servers, mail servers, and other network services that utilize TLS encryption.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise the availability of critical network infrastructure. Attackers can exploit this flaw by crafting specially crafted TLS messages containing multiple Client Hello sequences, which when processed by vulnerable gnutls-serv implementations cause immediate system crashes. This creates a persistent denial of service condition that can be exploited repeatedly, allowing attackers to maintain ongoing disruption of services without requiring significant resources or advanced technical skills. The vulnerability is particularly concerning because it affects the core TLS implementation functionality, meaning that any application or service using GnuTLS for secure communications becomes vulnerable to this attack vector, including web servers, database servers, and other network services that depend on TLS for secure data transmission.
Mitigation strategies for CVE-2008-1949 primarily focus on updating to patched versions of GnuTLS, specifically version 2.2.4 or later, which contain the necessary fixes for proper message sequence validation. System administrators should prioritize patching all affected systems and applications that rely on GnuTLS for secure communications, as the vulnerability can be exploited remotely without authentication. Additional defensive measures include implementing network-level monitoring to detect unusual TLS message patterns and configuring intrusion detection systems to identify potential exploitation attempts. The vulnerability aligns with CWE-476 which describes NULL pointer dereference conditions, and represents a classic example of improper input validation in cryptographic protocol implementations. From an ATT&CK framework perspective, this vulnerability maps to the privilege escalation and denial of service tactics, as it allows adversaries to disrupt services and potentially gain unauthorized access to network resources through carefully crafted TLS handshake messages that exploit the library's failure to properly validate message sequences and maintain correct protocol state. Organizations should also consider implementing network segmentation and access controls to limit the potential impact of such attacks on their overall infrastructure.