CVE-2016-7444 in GnuTLS
Summary
by MITRE
The gnutls_ocsp_resp_check_crt function in lib/x509/ocsp.c in GnuTLS before 3.4.15 and 3.5.x before 3.5.4 does not verify the serial length of an OCSP response, which might allow remote attackers to bypass an intended certificate validation mechanism via vectors involving trailing bytes left by gnutls_malloc.
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Analysis
by VulDB Data Team • 09/21/2022
The vulnerability identified as CVE-2016-7444 affects the GnuTLS library's implementation of Online Certificate Status Protocol handling, specifically within the gnutls_ocsp_resp_check_crt function located in lib/x509/ocsp.c. This flaw exists in versions prior to 3.4.15 and 3.5.x prior to 3.5.4, representing a critical security oversight that undermines the certificate validation process. The issue stems from insufficient validation of the serial number length within OCSP responses, creating a potential attack vector that could be exploited by remote adversaries to circumvent intended security controls.
The technical nature of this vulnerability involves a memory management flaw where the function fails to properly validate the length of certificate serial numbers contained within OCSP responses. When gnutls_malloc allocates memory for certificate serial numbers, trailing bytes may remain unverified, allowing attackers to craft malicious OCSP responses that appear valid but contain manipulated serial number data. This weakness enables attackers to bypass certificate validation mechanisms that rely on OCSP responses to determine certificate status, effectively undermining the trust model that SSL/TLS connections depend upon. The vulnerability operates at the intersection of memory management and cryptographic validation, where improper bounds checking allows for data manipulation that could be used to validate compromised certificates.
The operational impact of this vulnerability is significant as it directly affects the integrity of certificate validation processes in systems using GnuTLS versions prior to the patched releases. Attackers could exploit this flaw to present fraudulent certificates that would be accepted by vulnerable systems, potentially enabling man-in-the-middle attacks, certificate impersonation, and unauthorized access to secure communications. Systems that rely on OCSP for certificate status checking become particularly vulnerable, as the flaw allows attackers to manipulate certificate validation outcomes without detection. This vulnerability affects a wide range of applications including web servers, email clients, and any software that utilizes GnuTLS for secure communications, making it a critical concern for organizations maintaining secure network infrastructure.
Mitigation strategies for CVE-2016-7444 primarily involve upgrading to patched versions of GnuTLS, specifically version 3.4.15 or later for the 3.4.x branch, and version 3.5.4 or later for the 3.5.x branch. Organizations should also implement monitoring for suspicious certificate validation behaviors and consider implementing additional certificate validation layers beyond OCSP checking. The vulnerability aligns with CWE-129, which addresses insufficient input validation, and represents a variant of memory corruption issues that can be mapped to ATT&CK technique T1556.301, specifically related to credential access through manipulation of cryptographic validation mechanisms. Security teams should also review their certificate validation policies and consider implementing certificate pinning or other mechanisms that provide additional layers of protection against certificate manipulation attacks.