CVE-2017-7507 in GnuTLS
Summary
by MITRE
GnuTLS version 3.5.12 and earlier is vulnerable to a NULL pointer dereference while decoding a status response TLS extension with valid contents. This could lead to a crash of the GnuTLS server application.
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Analysis
by VulDB Data Team • 12/08/2022
The vulnerability identified as CVE-2017-7507 affects GnuTLS versions 3.5.12 and earlier, representing a critical NULL pointer dereference flaw within the TLS extension processing mechanism. This vulnerability specifically manifests during the decoding of status response TLS extensions, where the application fails to properly validate pointer references before dereferencing them. The flaw exists in the cryptographic library's handling of TLS protocol extensions, particularly those related to certificate status responses that are used in protocols such as OCSP stapling. When a maliciously crafted TLS handshake contains a specially formatted status response extension with valid contents, the GnuTLS server processes this extension without adequate null pointer checks, leading to an immediate application crash. This behavior represents a denial of service condition that can be exploited by remote attackers without authentication requirements.
The technical nature of this vulnerability aligns with CWE-476, which describes NULL pointer dereference conditions in software implementations. The flaw occurs within the TLS extension parsing logic where the application assumes certain pointers will always contain valid references, failing to implement proper validation before memory access operations. The vulnerability demonstrates a classic software error pattern where defensive programming practices are insufficiently applied to handle edge cases in protocol parsing. When the server encounters a valid but improperly structured status response extension, the parsing routine attempts to access memory locations through null pointers, causing an immediate segmentation fault or access violation that terminates the application process. This type of vulnerability is particularly dangerous in server environments where availability is critical for service continuity and where automated exploitation can lead to sustained denial of service conditions.
The operational impact of CVE-2017-7507 extends beyond simple service disruption, as it can be leveraged in broader attack scenarios within the MITRE ATT&CK framework under the technique of "Denial of Service" (T1499). Systems running vulnerable GnuTLS versions become susceptible to remote exploitation where attackers can reliably crash server processes through carefully crafted TLS handshakes. This vulnerability affects any application or service that relies on GnuTLS for TLS implementation, including web servers, mail servers, database servers, and other network services. The crash condition results in immediate service unavailability, requiring manual intervention for system recovery and potentially enabling attackers to perform persistent disruption attacks. The vulnerability can be exploited at scale across multiple systems simultaneously, making it particularly attractive for coordinated denial of service campaigns. Organizations using affected versions may experience cascading failures if the vulnerable services are part of critical infrastructure or if they depend on other services that could be similarly affected.
Mitigation strategies for CVE-2017-7507 primarily involve immediate version upgrades to GnuTLS 3.5.13 or later, which contain patches addressing the NULL pointer dereference condition. System administrators should prioritize patching affected systems and conducting thorough vulnerability assessments to identify all instances of vulnerable GnuTLS installations. Network monitoring should be enhanced to detect unusual TLS handshake patterns that might indicate exploitation attempts. Additionally, implementing proper input validation and defensive programming practices within applications that utilize GnuTLS can provide additional layers of protection. Organizations should consider deploying intrusion detection systems that can identify and alert on suspicious TLS extension patterns, particularly those that might trigger the vulnerable code paths. The patch resolution for this vulnerability demonstrates the importance of maintaining current cryptographic library versions and implementing regular security updates as part of comprehensive vulnerability management programs.