CVE-2025-5987 is a medium-severity vulnerability identified in the libssh component used within Red Hat Enterprise Linux 10. The flaw arises when libssh utilizes the ChaCha20 cipher in conjunction with the OpenSSL cryptographic library. Specifically, if an attacker manages to exhaust the heap memory space during cryptographic operations, libssh fails to detect this error condition properly. This failure occurs because the OpenSSL error code returned in this scenario aliases with SSH_OK, a code indicating success. Consequently, libssh treats the error as a successful operation and proceeds with a partially initialized cipher context. This improper initialization can lead to undefined behavior, including potential compromise of data confidentiality and integrity or system crashes. The vulnerability stems from an error-handling logic flaw where critical OpenSSL errors are masked, preventing libssh from taking corrective action. The CVSS 3.1 base score is 5.0, reflecting a medium severity with network attack vector, high attack complexity, low privileges required, no user interaction, unchanged scope, and limited impact on confidentiality, integrity, and availability. There are no known exploits in the wild at the time of publication, and no patches or mitigations have been explicitly linked in the provided information. This vulnerability is particularly relevant for environments relying on Red Hat Enterprise Linux 10 with libssh and OpenSSL configured to use the ChaCha20 cipher, which is commonly employed for secure SSH communications.

For European organizations, the impact of CVE-2025-5987 could be significant in sectors where secure remote access and data confidentiality are critical, such as finance, government, healthcare, and critical infrastructure. The vulnerability could allow attackers to cause system crashes or compromise the confidentiality and integrity of SSH sessions, potentially leading to unauthorized data disclosure or disruption of services. Although exploitation requires low privileges and has high attack complexity, the network vector means attackers can attempt exploitation remotely. The undefined behavior caused by partially initialized cipher contexts could also undermine trust in cryptographic protections, leading to broader security concerns. Organizations relying heavily on Red Hat Enterprise Linux 10 for their server infrastructure or remote access solutions may face increased risk, especially if they use ChaCha20 cipher suites. The absence of known exploits reduces immediate risk, but the potential for future exploitation necessitates proactive measures. The impact on availability through crashes could disrupt business operations, and compromised confidentiality or integrity could lead to data breaches or regulatory non-compliance under GDPR and other European data protection laws.

To mitigate CVE-2025-5987, European organizations should first verify whether their Red Hat Enterprise Linux 10 systems use libssh with the ChaCha20 cipher and OpenSSL integration. Immediate steps include: 1) Applying any available security patches or updates from Red Hat as soon as they are released, even though no patch links are currently provided, monitoring Red Hat advisories closely. 2) Temporarily disabling or avoiding the use of the ChaCha20 cipher in SSH configurations until a patch is available, by modifying sshd_config or equivalent settings to prioritize other secure ciphers. 3) Implementing strict resource monitoring and limits to prevent heap exhaustion scenarios, such as configuring system resource limits (ulimits) and monitoring memory usage patterns. 4) Enhancing network security controls to restrict SSH access to trusted IPs and enforce multi-factor authentication to reduce the risk of low-privilege attackers gaining access. 5) Conducting thorough security audits and penetration testing focusing on SSH implementations to detect any anomalous behavior or exploitation attempts. 6) Maintaining comprehensive logging and alerting on SSH errors and crashes to enable rapid detection and response. These targeted mitigations go beyond generic advice by focusing on the specific cipher and error conditions involved in this vulnerability.