CVE-2022-49077 is a vulnerability identified in the Linux kernel related to the mremap() system call, specifically when invoked with an old_size parameter of zero. The issue arises in the kernel source file mmmremap.c, where the function move_page_tables() calls invalidate_range_start() and invalidate_range_end() unnecessarily with an empty memory range. This behavior triggers warnings (WARN) in the Kernel-based Virtual Machine (KVM) subsystem's mmu_notifier component. Historically, empty ranges in such contexts have been indicative of off-by-one bugs, so the kernel emits warnings to detect potentially buggy callers. However, in this case, the empty range is caused by userspace invoking mremap() with old_size=0, which is considered a misuse or 'silly' behavior rather than a kernel bug. The fix implemented involves an early return in move_page_tables() to avoid these pointless invalidation calls when old_size is zero, thereby preventing the warnings. This vulnerability does not appear to cause memory corruption, privilege escalation, or denial of service directly, but it does generate kernel warnings that could potentially be leveraged for information leakage or to disrupt normal kernel logging. There are no known exploits in the wild, and the vulnerability affects Linux kernel versions identified by the commit hash 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2. No CVSS score has been assigned to this vulnerability.

For European organizations, the impact of CVE-2022-49077 is relatively low in terms of direct security consequences. The vulnerability primarily results in kernel warnings due to unnecessary invalidation calls when mremap() is misused with old_size=0. While this does not directly lead to system compromise, it could cause increased kernel log noise, potentially masking other critical events or leading to minor performance degradation in virtualized environments using KVM. In environments with strict monitoring and alerting on kernel warnings, this could generate false positives or alert fatigue. Additionally, if an attacker can induce this condition repeatedly, it might be used as a low-level denial-of-service vector by flooding kernel logs or triggering unexpected behavior in memory management subsystems. However, since exploitation requires invoking mremap() with specific parameters and does not escalate privileges or corrupt memory, the overall risk remains limited. European organizations running Linux-based virtualized infrastructure, especially those using KVM, should be aware but not overly concerned about immediate threats from this vulnerability.

To mitigate CVE-2022-49077, European organizations should apply the Linux kernel patch that introduces an early return in move_page_tables() to prevent unnecessary invalidation calls when old_size=0 in mremap(). This patch is the definitive fix and should be incorporated into kernel updates as soon as they become available from trusted Linux distributions. Organizations should prioritize updating kernels on systems running KVM virtualization, as these are the most directly affected. Additionally, administrators should audit and restrict userspace applications and scripts to avoid invoking mremap() with old_size=0, which is an unusual and potentially erroneous usage pattern. Monitoring kernel logs for repeated WARN messages related to mmu_notifier can help identify attempts to trigger this condition. Implementing strict access controls on who can execute or develop low-level memory management utilities can further reduce the risk of accidental or malicious exploitation. Finally, maintaining up-to-date kernel versions and subscribing to vendor security advisories will ensure timely awareness and remediation of this and similar vulnerabilities.