CVE-2017-7502 in NSS
Summary
by MITRE
Null pointer dereference vulnerability in NSS since 3.24.0 was found when server receives empty SSLv2 messages resulting into denial of service by remote attacker.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 12/07/2022
The vulnerability identified as CVE-2017-7502 represents a critical null pointer dereference flaw within the Network Security Services (NSS) cryptographic library version 3.24.0 and later. This vulnerability specifically manifests when an NSS-based server encounters empty SSLv2 protocol messages during normal operation. The issue stems from inadequate input validation and error handling mechanisms within the SSLv2 message processing routines, where the system attempts to dereference a null pointer when processing malformed or empty protocol frames. This flaw exists in the cryptographic protocol stack that governs secure communications between network endpoints.
The technical exploitation of this vulnerability occurs through a remote attacker who can craft and transmit specially formatted empty SSLv2 messages to a vulnerable NSS server. When the server processes these malformed messages, the NSS library fails to properly validate the incoming data structure, leading to a scenario where a null pointer reference is encountered during the message parsing phase. This results in an immediate system crash or termination of the affected service, effectively causing a denial of service condition that impacts legitimate users attempting to establish secure connections. The vulnerability is classified under CWE-476 as a null pointer dereference, which represents a fundamental programming error where code attempts to access memory through a null reference.
From an operational perspective, this vulnerability poses significant risk to organizations relying on NSS-based services such as web servers, email servers, or any application that utilizes the NSS library for secure communications. The remote nature of the attack means that adversaries can exploit this flaw from anywhere on the network without requiring local access or authentication credentials. The impact extends beyond simple service disruption as it can affect the availability of critical infrastructure components, potentially leading to extended downtime and business continuity issues. Attackers can leverage this vulnerability to perform sustained denial of service attacks against targeted systems, making it particularly dangerous in environments where availability is paramount.
The mitigation strategies for CVE-2017-7502 primarily involve upgrading to patched versions of the NSS library where the vulnerability has been addressed through proper input validation and null pointer checks. Organizations should prioritize updating their NSS implementations to versions that include the necessary security patches, typically those released after the vulnerability disclosure. Additionally, network administrators can implement temporary protective measures such as disabling SSLv2 protocol support entirely, as this protocol is considered obsolete and inherently insecure. The ATT&CK framework categorizes this type of vulnerability under privilege escalation and denial of service tactics, where the null pointer dereference represents a specific technique for achieving system instability. Organizations should also consider implementing network monitoring solutions that can detect anomalous SSLv2 traffic patterns and alert administrators to potential exploitation attempts. Regular security assessments and vulnerability scanning should include checks for NSS versions to ensure compliance with security best practices and prevent exploitation of this and similar vulnerabilities.