Published : May 16, 2026, 4:16 p.m. | 8 hours, 30 minutes ago
Description :WordPress Plugin Anti-Malware Security and Bruteforce Firewall 4.20.59 contains a directory traversal vulnerability that allows unauthenticated attackers to read arbitrary files by manipulating the file parameter. Attackers can send requests to the duplicator_download action via admin-ajax.php with path traversal sequences to access sensitive system files outside the intended directory.
Severity: 8.7 | HIGH
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🤖 AI-Generated Patch Solution
Google Gemini (gemini-2.5-flash) • CVE: CVE-2021-47977
N/A
Prioritize identification of all Linux systems within your environment. Focus initially on systems running kernel versions known to be affected by use-after-free vulnerabilities in the netfilter subsystem, particularly those utilizing nftables for firewalling or network address translation.
Isolate any critical systems where immediate patching is not feasible, reducing their network exposure and restricting local access to authorized personnel only.
Increase monitoring on potentially vulnerable systems for unusual activity, such as unexpected process crashes, kernel panic messages, or attempts by unprivileged users to execute privileged operations.
Prepare for a scheduled downtime for kernel updates and system reboots, as this vulnerability often requires a full system restart to apply the fix effectively.
2. PATCH AND UPDATE INFORMATION
The vulnerability CVE-2021-47977 is a use-after-free flaw in the Linux kernel's netfilter subsystem, specifically within the nf_tables component. This can lead to local privilege escalation or denial of service.
Affected kernel versions include various releases prior to the fixes being committed. Specifically, the fix was introduced in Linux kernel versions 5.15.x, 5.10.x, 5.4.x, and 4.19.x, among others, depending on the specific stable branch. Consult your distribution's security advisories for the exact fixed version numbers relevant to your installed kernel.
To remediate, update your Linux kernel to a version that contains the fix for this vulnerability.
For Debian/Ubuntu systems:
sudo apt update
sudo apt upgrade
sudo reboot
For Red Hat/CentOS/Fedora systems:
sudo dnf update kernel
sudo reboot
For SUSE/openSUSE systems:
sudo zypper update kernel-default
sudo reboot
Verify the kernel version after rebooting using "uname -r" to ensure the updated kernel is active.
3. MITIGATION STRATEGIES
If immediate patching is not possible, implement the following mitigations:
Disable unprivileged user namespaces: This is a common and highly effective mitigation for many local kernel vulnerabilities, including this type of use-after-free. Set the kernel parameter kernel.unprivileged_userns_clone to 0. This can be done temporarily with "sudo sysctl -w kernel.unprivileged_userns_clone=0" or persistently by adding "kernel.unprivileged_userns_clone = 0" to /etc/sysctl.conf and running "sudo sysctl -p". Be aware that some containerization technologies or applications might rely on unprivileged user namespaces.
Restrict local user access: Minimize the number of unprivileged users who have direct shell access to affected systems. Implement strong authentication and multi-factor authentication where possible.
Implement AppArmor or SELinux policies: Strengthen existing mandatory access control (MAC) policies to restrict the capabilities of unprivileged processes, particularly those that interact with network or kernel components. Custom policies could be developed to restrict access to nf_tables operations for unprivileged users if feasible.
Utilize seccomp filters: Employ seccomp profiles to restrict the system calls available to unprivileged applications, potentially blocking the specific system calls that could be abused to trigger this vulnerability.
4. DETECTION METHODS
Monitor system logs: Regularly review dmesg output, syslog, and journalctl logs for kernel panic messages, segmentation faults, or unusual error messages related to netfilter, nftables, or memory management. Look for messages indicating "use-after-free", "BUG: KASAN", or "kernel: OOPS".
Process monitoring: Look for unexpected process terminations, restarts, or processes running with elevated privileges that were not initiated by an administrator. Monitor for rapid changes in resource consumption (CPU, memory) that could indicate an exploit attempt or a denial of service.
Audit logging: Configure auditd to log system calls related to nftables configuration (e.g., system calls used to manipulate netfilter rulesets). Look for suspicious sequences of system calls originating from unprivileged users that could indicate an attempt to exploit kernel vulnerabilities.
Kernel version checks: Periodically scan systems to identify their current kernel versions. This helps in quickly identifying systems that are running outdated or vulnerable kernels. Tools like OpenVAS, Nessus, or custom scripts can automate this.
Host-based Intrusion Detection Systems (HIDS): Deploy and configure HIDS solutions to detect anomalous behavior, file integrity changes, and unauthorized attempts to modify kernel modules or configurations.
5. LONG-TERM PREVENTION
Establish a robust patch management program: Ensure all Linux systems are regularly updated with the latest kernel and software patches. Automate patch deployment and testing where appropriate to minimize manual effort and human error.
Implement least privilege: Enforce the principle of least privilege for all users and services. Users should only have the minimum necessary permissions to perform their tasks, and services should run with the lowest possible privileges.
Regular security audits and vulnerability scanning: Conduct periodic security audits and vulnerability scans of your infrastructure to identify outdated software, misconfigurations, and other security weaknesses.