CVE-2026-53219

What it actually does

This is a Linux kernel information disclosure flaw in the netfilter x_tables get-entries code paths for IPv4, IPv6, and ARP tables, including native and compat interfaces. During a rule-table read, the kernel could copy a rule entry header containing an internal per-CPU counter pointer to user space before replacing the counter fields with sanitized counter values. If the user-supplied destination buffer faults at the right point, the syscall can fail with EFAULT while leaving the raw kernel pointer visible to the caller. The flaw does not directly provide code execution or privilege escalation, but it can disclose kernel memory addresses and help defeat address-space randomization protections used to make kernel exploitation harder.

Why it matters to the business

The primary risk is that a local attacker, compromised workload, or containerized process with the required netfilter access could obtain kernel address information that improves the reliability of a separate kernel exploit. By itself, this issue is unlikely to cause service outage or data theft, and current public exploitation signals are low: EPSS is 0.00123, it is not listed in CISA KEV, and no exploit maturity is currently reported. However, because Linux kernels are widely deployed and kernel information leaks are commonly chained with memory-corruption flaws, remediation should be included in normal kernel patch cycles and prioritized for multi-tenant hosts, container platforms, and systems allowing untrusted users or user namespaces.

How an attack unfolds

An attacker first needs local code execution with the ability to reach the affected x_tables get-entries interface, typically through netfilter-related getsockopt operations and, depending on kernel configuration and namespace policy, capabilities such as CAP_NET_ADMIN in a relevant network namespace. The attacker prepares or maps a user-space buffer so that copying the x_tables entry header succeeds far enough to include the per-CPU counter pointer, but then faults before the kernel overwrites the counter fields with sanitized values. The kernel returns an EFAULT error, but the partially copied buffer can retain the leaked kernel pointer. The attacker then uses that pointer to infer kernel layout information, such as defeating KASLR, and may combine it with a separate kernel vulnerability that requires address knowledge for reliable exploitation.

How to fix it

Apply a Linux kernel update from the relevant distribution or vendor that includes the upstream fix for netfilter x_tables to copy only the entry prefix before counters and then copy sanitized counter snapshots into the counter field. Because no exact product or package fixed versions were provided, track vendor advisories for kernels containing the patch titled "netfilter: x_tables: avoid leaking percpu counter pointers" or equivalent backports. Reboot into the fixed kernel unless a validated livepatch is available. As interim risk reduction, restrict untrusted local shell access, avoid granting CAP_NET_ADMIN to containers or untrusted workloads, disable or tightly control unprivileged user namespaces where operationally feasible, and minimize use of legacy x_tables/iptables interfaces where nftables-only configurations are possible. These mitigations reduce exploit reachability but should not be treated as complete fixes.

How to confirm the fix worked

Confirm remediation by verifying the running kernel package and build include the vendor backport for the x_tables counter pointer leak fix, not merely that the package is installed. Check the active kernel with uname -r and compare it against the distribution advisory or changelog containing the netfilter x_tables fix. Ensure systems have rebooted or are running a livepatch that explicitly covers this issue. In a controlled lab only, a purpose-built regression test can attempt the faulting get-entries sequence and verify that no kernel pointer-like value is left in the user buffer after EFAULT. Operationally, also validate that untrusted containers and users do not have unnecessary CAP_NET_ADMIN or network namespace privileges that would expose the affected interface.

Typical attack path

1. Gain local execution on a Linux system or inside a workload/container where netfilter x_tables interfaces are reachable.
2. Obtain the required namespace capability or access path to query IPv4, IPv6, or ARP x_tables rule entries.
3. Create a user-space destination buffer that intentionally faults during the get-entries copy operation after the rule header has been partially copied.
4. Invoke the affected native or compat get-entries operation through the netfilter getsockopt interface.
5. Read the partially copied user-space buffer after the syscall fails with EFAULT to recover a raw per-CPU counter pointer.
6. Use the leaked kernel address information to reduce kernel exploit mitigations, most notably KASLR, when chaining with another vulnerability.

How to detect it

There is no reliable, product-wide forensic artifact that proves exploitation of this information leak after the fact, because successful leakage can occur through normal kernel interfaces and may only produce a failed syscall. Detection should focus on high-risk behavioral evidence: local processes repeatedly querying netfilter x_tables entries, unusual getsockopt activity against ip_tables/ip6_tables/arp_tables, repeated EFAULT results from netfilter get-entries operations, unexpected use of CAP_NET_ADMIN by untrusted processes or containers, and nearby evidence of kernel exploit chaining such as crashes, oops messages, privilege changes, module loading attempts, or suspicious namespace creation. Useful sources include Linux auditd syscall logs if configured, eBPF/EDR telemetry, container runtime audit events, kernel logs from dmesg or journald, capability-change events, and process execution telemetry for unusual iptables, ip6tables, arptables, or custom binaries. Absence of these logs does not rule out exploitation.

• IPT_SO_GET_ENTRIES
• IP6T_SO_GET_ENTRIES
• ARPT_SO_GET_ENTRIES
• xt_entry_match
• ip_tables
• ip6_tables
• arp_tables
• CAP_NET_ADMIN
• EFAULT

What your security team should do

• Inventory Linux systems running kernels with netfilter x_tables support, especially container hosts, multi-user servers, virtualization hosts, and internet-facing appliances built on Linux.
• Prioritize kernel updates for systems where untrusted local code can run, where containers are granted CAP_NET_ADMIN, or where unprivileged user namespaces are enabled.
• Apply vendor kernel updates containing the x_tables counter pointer leak fix and reboot or confirm effective livepatch coverage.
• Review container and workload policies to remove CAP_NET_ADMIN unless explicitly required.
• Restrict unprivileged user namespaces where feasible and monitor exceptions through formal risk acceptance.
• Treat any observed exploitation signal as potentially preparatory activity for a chained kernel exploit, and investigate for accompanying privilege-escalation attempts.
• Because the issue is not currently in CISA KEV, has no reported public exploit maturity, and has low EPSS, schedule remediation through standard kernel patch management unless high-risk local multi-tenant exposure exists.