CVE-2014-5139 in OpenSSL
Summary
by MITRE
The ssl_set_client_disabled function in t1_lib.c in OpenSSL 1.0.1 before 1.0.1i allows remote SSL servers to cause a denial of service (NULL pointer dereference and client application crash) via a ServerHello message that includes an SRP ciphersuite without the required negotiation of that ciphersuite with the client.
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Analysis
by VulDB Data Team • 02/10/2022
The vulnerability described in CVE-2014-5139 represents a critical denial of service flaw within OpenSSL's SSL/TLS implementation that affects versions prior to 1.0.1i. This issue manifests when remote SSL servers craft malicious ServerHello messages containing SRP (Secure Remote Password) ciphersuites without proper negotiation with the client. The flaw resides in the ssl_set_client_disabled function within the t1_lib.c file, which fails to properly validate ciphersuite negotiations before attempting to process them. This represents a classic null pointer dereference vulnerability that can be exploited by remote attackers to crash client applications that use OpenSSL.
The technical exploitation of this vulnerability occurs through a specific protocol sequence where an attacker-controlled SSL server sends a ServerHello message that includes an SRP ciphersuite in its cipher suite list. However, this ciphersuite has not been properly negotiated with the client during the handshake process. When the OpenSSL client processes this malformed ServerHello message, the ssl_set_client_disabled function attempts to access a null pointer reference when handling the SRP ciphersuite, leading to an immediate application crash. This behavior directly violates the principle of proper input validation and error handling that should be implemented in cryptographic libraries.
From an operational impact perspective, this vulnerability poses significant risks to any system that relies on OpenSSL for SSL/TLS connections, particularly web servers, email servers, and other network services that may be targeted by such attacks. The denial of service aspect means that legitimate users could be denied access to services, while the potential for application crashes could lead to extended downtime and service disruption. The vulnerability affects a wide range of applications that depend on OpenSSL, including but not limited to Apache web servers, nginx, and various mail and database servers that implement SSL/TLS protocols.
The underlying cause of this vulnerability aligns with CWE-476 which describes NULL pointer dereferences, and it can be mapped to ATT&CK technique T1499.004 which covers network denial of service attacks. Organizations should implement immediate mitigations including updating to OpenSSL 1.0.1i or later versions, which contain the necessary patches to properly validate ciphersuite negotiations. Additional protective measures include implementing network-level firewalls to filter suspicious SSL handshakes, monitoring for unusual SSL server behavior, and ensuring that all systems are regularly updated with security patches. The vulnerability also highlights the importance of proper error handling in cryptographic libraries and demonstrates the critical need for thorough testing of SSL/TLS implementations against malformed inputs. Organizations should conduct vulnerability assessments to identify systems running affected OpenSSL versions and prioritize patching efforts to prevent exploitation of this and similar denial of service vulnerabilities in their infrastructure.