CVE-2025-32989 in GnuTLS
Summary
by MITRE • 07/10/2025
A heap-buffer-overread vulnerability was found in GnuTLS in how it handles the Certificate Transparency (CT) Signed Certificate Timestamp (SCT) extension during X.509 certificate parsing. This flaw allows a malicious user to create a certificate containing a malformed SCT extension (OID 1.3.6.1.4.1.11129.2.4.2) that contains sensitive data. This issue leads to the exposure of confidential information when GnuTLS verifies certificates from certain websites when the certificate (SCT) is not checked correctly.
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Analysis
by VulDB Data Team • 11/28/2025
The heap-buffer-overread vulnerability identified as CVE-2025-32989 represents a critical flaw in the GnuTLS cryptographic library's handling of Certificate Transparency (CT) Signed Certificate Timestamp (SCT) extensions within X.509 certificates. This vulnerability specifically manifests during the parsing of SCT extensions with the well-known OID 1.3.6.1.4.1.11129.2.4.2, where the library fails to properly validate the structure and bounds of the extension data. The flaw stems from inadequate input validation mechanisms that permit malformed SCT data to be processed without proper boundary checks, creating a scenario where the memory access operations extend beyond the allocated buffer boundaries. This type of vulnerability falls under the CWE-125 category of Out-of-bounds Read, which is classified as a fundamental memory safety issue that can lead to information disclosure and potentially more severe exploitation vectors.
The operational impact of this vulnerability extends beyond simple information exposure, as it creates a potential attack surface that could be exploited by adversaries to extract sensitive data from memory locations adjacent to the parsed SCT extension. When GnuTLS processes certificates containing malformed SCT extensions, the library's certificate verification routine attempts to read data beyond the intended buffer boundaries, potentially exposing stack contents, heap data, or other sensitive information that may contain cryptographic keys, session tokens, or other confidential material. This vulnerability particularly affects systems that rely on GnuTLS for SSL/TLS certificate validation, including web servers, email servers, and any application that utilizes the library for secure communications. The attack vector requires a malicious certificate to be presented to a vulnerable GnuTLS implementation, making it a server-side vulnerability that could be leveraged in man-in-the-middle scenarios or when systems are configured to validate certificates from untrusted sources.
The security implications of this vulnerability align with ATT&CK technique T1552.001 for Unsecured Credentials and T1071.004 for Application Layer Protocol: DNS, as it enables adversaries to potentially extract sensitive information that could be used for further attacks. The flaw represents a classic example of how improper input validation can lead to memory corruption vulnerabilities, where the lack of proper bounds checking during certificate parsing creates opportunities for information disclosure. Organizations using GnuTLS in production environments face significant risk as this vulnerability could be exploited to recover sensitive data that was not intended to be exposed through normal certificate validation processes. The vulnerability's impact is particularly concerning given that Certificate Transparency is a critical component of modern certificate validation practices, and the flaw specifically targets the mechanisms designed to prevent certificate misissuance and improve transparency in certificate authority operations.
Mitigation strategies for CVE-2025-32989 should prioritize immediate patching of affected GnuTLS versions, as the vulnerability requires no special privileges to exploit and can be triggered through standard certificate validation operations. System administrators should implement certificate pinning mechanisms where possible to reduce the attack surface, and organizations should monitor their certificate validation processes to ensure that SCT extensions are properly validated before being processed. Network segmentation and monitoring solutions should be deployed to detect anomalous certificate validation patterns that might indicate exploitation attempts. Additionally, the vulnerability highlights the importance of comprehensive input validation in cryptographic libraries and demonstrates the need for regular security assessments of critical infrastructure components. The remediation process should include thorough testing of patched systems to ensure that certificate validation continues to function correctly while preventing the heap-buffer-overread condition from occurring. Organizations should also consider implementing certificate transparency monitoring to detect and respond to potentially malicious certificates that might exploit this vulnerability.