CVE-2025-13151 is a stack-based buffer overflow vulnerability identified in the libtasn1 library version 4.20.0, a component of the widely used GnuTLS cryptographic library. The vulnerability arises from improper input size validation in the function asn1_expend_octet_string, which processes ASN.1 octet strings. ASN.1 is a standard interface description language for defining data structures used in cryptography and network protocols. The failure to check the size of input data before copying it into a fixed-size buffer leads to a classic buffer overflow (CWE-120), which can overwrite adjacent memory on the stack. This can cause application crashes or potentially allow an attacker to execute arbitrary code, depending on the exploitation context. The CVSS v3.1 score of 7.5 reflects a high severity, with an attack vector of network (AV:N), low attack complexity (AC:L), no privileges required (PR:N), no user interaction (UI:N), unchanged scope (S:U), and impact limited to availability (A:H) without affecting confidentiality or integrity. This suggests the primary impact is denial of service, though code execution cannot be ruled out without further details. No known exploits are currently reported in the wild, but the vulnerability is publicly disclosed and should be considered a serious risk for applications using libtasn1, including VPNs, mail servers, and other TLS-enabled services. The lack of an available patch at the time of disclosure necessitates immediate risk mitigation strategies. The vulnerability affects all deployments using the vulnerable libtasn1 version, which is common in open-source environments and embedded systems.

For European organizations, the primary impact of CVE-2025-13151 is the potential for denial of service attacks against critical infrastructure and services relying on GnuTLS for secure communications. This includes web servers, mail servers, VPN gateways, and other network appliances that use libtasn1 for ASN.1 parsing. Disruption of these services can affect business continuity, data availability, and operational reliability. While the vulnerability currently does not indicate compromise of confidentiality or integrity, denial of service can still have severe consequences, especially for sectors like finance, healthcare, and government services that require high availability. Additionally, if future exploit techniques evolve to enable code execution, the risk profile would escalate significantly. European organizations with embedded systems or IoT devices using GnuTLS may face challenges in patching and mitigating the vulnerability promptly, increasing exposure. The absence of known exploits provides a window for proactive defense, but the public disclosure increases the risk of reverse-engineered exploits emerging. Organizations must assess their exposure based on their use of libtasn1 and prioritize remediation accordingly.

1. Monitor official GnuTLS and libtasn1 project channels for patches addressing CVE-2025-13151 and apply updates immediately upon release. 2. In the interim, implement network-level protections such as intrusion detection/prevention systems (IDS/IPS) to detect anomalous ASN.1 traffic patterns that may indicate exploitation attempts. 3. Employ runtime protections including stack canaries, Address Space Layout Randomization (ASLR), and Data Execution Prevention (DEP) on affected systems to reduce exploitation success. 4. Conduct an inventory of all software and devices using libtasn1 to identify vulnerable versions and prioritize patching or mitigation. 5. For embedded and IoT devices where patching is difficult, consider network segmentation and strict access controls to limit exposure. 6. Review and harden TLS/SSL configurations to minimize attack surface, including disabling unnecessary services that rely on libtasn1. 7. Engage in threat hunting and monitoring for unusual crashes or service disruptions that could indicate exploitation attempts. 8. Collaborate with vendors and open-source communities to accelerate patch availability and deployment. 9. Educate system administrators and security teams about the vulnerability specifics to ensure rapid response.