Metasploit Adds ARMLE Support to CVE-2026-31431 Copy Fail Linux Root Exploit

Rapid7's May 8, 2026 Metasploit wrap-up expands the CVE-2026-31431 exploit module to support ARMLE (ARM little-endian — the instruction set used by many embedded systems, IoT devices, and Raspberry Pi-class hardware running Linux) targets, extending automated exploitation coverage for a Linux kernel privilege escalation bug that affects virtually every mainstream Linux distribution built since 2017. CVE-2026-31431, nicknamed "Copy Fail," carries a CVSS v3.1 score of 7.8 (rated High — locally exploitable, no authentication required beyond an initial low-privilege shell). A working 732-byte proof-of-concept exploit has been publicly available since the April 29 disclosure. The same Metasploit update improves the Apache Shiro rememberMe deserialization module, allowing operators to select the gadget chain for broader target compatibility.

CVE-2026-31431 Copy Fail: Technical Details

CVE-2026-31431 is a logic flaw in the Linux kernel's cryptography subsystem. The bug lives in authencesn — a kernel module implementing Authenticated Encryption with Associated Data (AEAD — a cryptographic mode that simultaneously encrypts data and authenticates its integrity) — when accessed through the AF_ALG socket interface (the kernel's API that lets userspace programs invoke kernel cryptographic primitives) in combination with the splice() system call (splice() is a zero-copy data-movement syscall that moves data between file descriptors and pipes without copying it through userspace).

The interaction creates a page cache corruption condition: the kernel mishandles reference counting on shared memory pages during the splice operation through the AF_ALG socket, triggering a use-after-free memory corruption (a class of bug where code accesses memory that has already been freed, allowing the attacker to control what was written to that address). The result is a local privilege escalation (LPE) — the attacker starts with any unprivileged shell account on the system and ends with full root access.

The CVSS v3.1 score of 7.8 (High) reflects:

• Attack Vector: Local — requires an existing shell or code execution on the target
• Attack Complexity: Low — no race conditions or special timing required
• Privileges Required: Low — any standard user account suffices
• User Interaction: None — no action from another user is needed
• Confidentiality / Integrity / Availability Impact: High — root access means full system compromise

The public PoC exploit is 732 bytes and has been independently verified on Ubuntu 24.04 LTS, Amazon Linux 2023, RHEL 10.1, and SUSE 16 without modification. AlmaLinux, CloudLinux, and CERT-EU have each published advisories and patch notifications.

CVE-2026-31431 CVE-2026-31431 was publicly disclosed on April 29, 2026. According to Sysdig's breakdown, the vulnerability was introduced in a kernel commit dating back to approximately 2017, meaning it has been silently present in production Linux kernels for roughly nine years.

Exploitation Status and Threat Landscape

As of May 9, 2026:

• PoC status: Public, functional, minimal size, architecture-independent logic
• Metasploit module: Active — exploit/linux/local/copy_fail_lpe, now with x64 and ARMLE payloads
• Active exploitation in the wild: Not yet confirmed by CISA or major threat intelligence sources
• CISA KEV (Known Exploited Vulnerabilities catalog — CISA's list of CVEs confirmed under active real-world exploitation): Not yet listed
• MITRE ATT&CK T1068 (Exploitation for Privilege Escalation — using a software vulnerability to elevate permissions): Directly applicable

The Metasploit integration is the key escalation event in this update cycle. Before this week's wrap-up, exploiting CVE-2026-31431 required manually adapting the PoC to the target architecture. The Rapid7 module automates:

• Payload delivery for linux/x64 (standard 64-bit Intel/AMD) and linux/armle targets
• Support for cmd/unix/python/meterpreter/reverse_tcp on x64 (a Python-based Meterpreter — Metasploit's advanced interactive shell — that establishes a reverse TCP connection back to the attacker)
• ARMLE linux/armle/exec payload execution for ARM little-endian Linux devices

This means any penetration tester or threat actor with a low-privilege shell on an unpatched x64 or ARMLE Linux system can now escalate to root through a standard Metasploit workflow with no manual adaptation required.

The same wrap-up improves the Apache Shiro exploit/multi/http/shiro_rememberme_v124_deserialize module. Apache Shiro is a Java authentication and authorization framework (software managing login and access control for web applications) used extensively in enterprise Java stacks. Shiro 1.2.4's rememberMe cookie deserialization flaw — a vulnerability where the server deserializes attacker-controlled Java objects from a cookie, executing embedded code — was patched in 2016 but unpatched legacy instances remain common. The module update enables operators to select from multiple deserialization gadget chains (pre-assembled sequences of existing Java classes that, when processed together, execute arbitrary code), improving reliability across different server-side Java environments.

Who Is Affected

CVE-2026-31431 affects all Linux kernels compiled from approximately 2017 onward until vendor-patched versions are applied. Confirmed affected distributions include:

• Ubuntu 18.04, 20.04, 22.04, 24.04 LTS
• Amazon Linux 2, 2023
• Red Hat Enterprise Linux 8, 9, 10.1
• SUSE Linux Enterprise Server 15, 16
• Debian 10, 11, 12
• AlmaLinux 8, 9
• Rocky Linux 8, 9

ARMLE Linux targets include Raspberry Pi devices, industrial IoT gateways running Raspbian or Debian ARM variants, and embedded network appliances in OT (Operational Technology — systems that monitor and control physical industrial processes) environments. With Metasploit now automating ARMLE exploitation, privilege escalation on a compromised edge device becomes trivial, and such devices are often positioned at network boundaries with access to both corporate and industrial segments.

Microsoft's analysis identifies Kubernetes and cloud environments as particularly high-risk: a compromised pod or container can use CVE-2026-31431 to escalate from container user to node root, then pivot across the cluster. Container workloads that share the host kernel — standard in non-isolated Kubernetes deployments — are fully exposed to this attack path.

CVE-2026-31431 is most dangerous as the second step in an attack chain. It doesn't provide initial access on its own, but any vulnerability that yields a low-privilege shell — a web shell from a CMS compromise, an RCE (Remote Code Execution) in a web application, an SSRF (Server-Side Request Forgery) that achieves code execution — can immediately be escalated to root on unpatched systems.

What You Should Do Right Now

• Apply vendor patches immediately to all Linux systems:

“bash # Debian/Ubuntu sudo apt update && sudo apt full-upgrade # RHEL / AlmaLinux / Rocky Linux sudo dnf update kernel # Amazon Linux 2023 sudo dnf update kernel “ CloudLinux offers a live-patch option that applies the fix without a reboot, suitable for production systems requiring high availability.

• Prioritize internet-facing Linux systems and Kubernetes nodes. Any system reachable from the internet that runs a web application has potential for initial access via other vulnerabilities; unpatched kernel = instant root escalation from any such foothold.

• Check AF_ALG accessibility on unpatched systems to confirm exposure:

“bash python3 -c "import socket; s = socket.socket(41, 5); print('AF_ALG accessible — verify patch status')" “ Exit code 0 with output on an unpatched system indicates the vulnerable code path is reachable.

• Apply seccomp or AppArmor policies to restrict AF_ALG socket creation for unprivileged processes if patching cannot be completed immediately. This limits the exploit's trigger mechanism without modifying the kernel.

• For Kubernetes environments: Verify pod security admission controls block CAP_NET_ADMIN and CAP_SYS_ADMIN capabilities in standard workloads. Ensure node OS images are in your patch pipeline and update base images in CI/CD pipelines.

• For ARMLE and IoT devices: Patch where vendor updates are available. For devices without kernel update mechanisms, network-segment them with restricted lateral movement. Monitor for unexpected outbound connections from IoT/OT hosts.

• Run CVE-2026-31431 in your next authorized internal penetration test using the Metasploit module to confirm patch status across Linux fleet, particularly on legacy or long-running instances.

Background: Understanding the Risk

Local privilege escalation vulnerabilities are routinely underestimated because they require initial access. In practice, LPE bugs are almost always chained: an attacker exploits a separate vulnerability to land a low-privilege shell, then uses the LPE to escalate. In web application attack chains, this pattern is extremely common — a web shell, a deserialization exploit, or a misconfigured web service gives a restricted shell (often www-data or nobody), and an LPE converts that limited access into full node compromise. CVE-2026-31431's nine-year lifespan in production kernels means it is present in long-term support images, cloud provider AMIs (Amazon Machine Images — base OS images for EC2 instances), and container base images that have not been rebuilt since 2017.

The Apache Shiro module improvement in the same Metasploit release reflects the continued relevance of decade-old Java deserialization vulnerabilities in enterprise environments. Shiro is embedded in many Java frameworks still running in production — Apache OFBiz, various Spring-based stacks, and custom enterprise portals — and unpatched instances of the rememberMe flaw remain a practical attack vector against organizations that have not audited their Java dependency inventory. The Metasploit module's new chain-selection capability makes previously unreliable exploitation attempts against certain Java environments reliable.

Taken together, this week's Metasploit additions — a broad-scope LPE now reaching ARM targets and an improved Java deserialization exploit — reflect the tooling maturation cycle that transforms disclosed vulnerabilities from researcher findings into operational attacker capabilities.

Conclusion

The expansion of the CVE-2026-31431 Metasploit module to ARMLE targets marks the transition from manual PoC to turnkey exploitation for one of the broadest-scope Linux kernel vulnerabilities in recent memory. Security teams should treat unpatched Linux systems — particularly cloud instances, Kubernetes nodes, and ARMLE IoT and OT devices — as at elevated risk for complete privilege compromise in any scenario where an attacker achieves initial low-privilege access by any means.