CVE-2025-55398 is a critical vulnerability identified in the mouse07410 asn1c parser, a fork of the vlm asn1c ASN.1 compiler, specifically affecting versions up to 0.9.29 as of March 2025. The vulnerability arises in the handling of Unaligned Packed Encoding Rules (UPER) encoded data, where the asn1c-generated decoders fail to properly enforce INTEGER constraints when the integer bounds are positive and exceed 32 bits in length. ASN.1 (Abstract Syntax Notation One) is widely used for defining data structures in telecommunications and network protocols, and UPER is a compact encoding rule for ASN.1 data. The failure to enforce these constraints means that malformed or maliciously crafted input data can bypass validation checks, potentially leading to incorrect processing of data. This can result in severe consequences such as memory corruption, buffer overflows, or logic errors, which attackers could exploit to execute arbitrary code, cause denial of service, or compromise data integrity and confidentiality. The vulnerability has a CVSS v3.1 score of 9.8, indicating critical severity with network attack vector, no required privileges or user interaction, and impacts on confidentiality, integrity, and availability. Although no known exploits are currently reported in the wild, the nature of the flaw and the critical score suggest a high risk of exploitation once exploit code becomes available. The vulnerability is classified under CWE-1284, which relates to improper enforcement of constraints in data processing components. No official patches or fixes have been linked yet, emphasizing the need for immediate attention from users of the affected software.

For European organizations, the impact of CVE-2025-55398 could be significant, particularly for those relying on telecommunications infrastructure, network equipment, or software systems that utilize the mouse07410 asn1c parser or its derivatives. Given ASN.1's prevalence in telecom protocols (e.g., 5G, LTE), network management, and security appliances, exploitation could lead to unauthorized access, data breaches, service disruptions, or even full system compromise. Critical sectors such as telecommunications providers, government agencies, financial institutions, and critical infrastructure operators in Europe could face operational outages or data integrity issues. The vulnerability's ability to be exploited remotely without authentication or user interaction increases the risk of widespread attacks. Additionally, the potential for attackers to execute arbitrary code or cause denial of service could disrupt essential services and erode trust in affected systems. The lack of patches increases exposure time, making proactive mitigation essential. Organizations may also face regulatory and compliance challenges under frameworks like GDPR if data confidentiality or availability is compromised due to this vulnerability.

To mitigate CVE-2025-55398 effectively, European organizations should: 1) Conduct an immediate inventory to identify all systems and applications using mouse07410 asn1c or its forks, especially those handling UPER-encoded ASN.1 data. 2) Engage with vendors and open-source communities to obtain or develop patches or updated versions that enforce proper INTEGER constraints for values exceeding 32 bits. 3) Implement strict input validation and filtering at network boundaries to detect and block malformed ASN.1 UPER data packets, potentially using deep packet inspection tools tailored for ASN.1 protocols. 4) Employ network segmentation to isolate vulnerable systems, limiting exposure to external networks. 5) Monitor network traffic and system logs for anomalous ASN.1 decoding errors or unusual activity indicative of exploitation attempts. 6) Consider deploying runtime application self-protection (RASP) or memory protection mechanisms (e.g., ASLR, DEP) to reduce exploitation success. 7) Prepare incident response plans specific to ASN.1-related attacks, including rapid patch deployment and system recovery procedures. 8) Stay informed about updates from the mouse07410 asn1c project and security advisories to apply fixes promptly once available.