CVE-2020-5847: Unraid Remote Code Execution Vulnerability

CVE-2020-5847 is a remote code execution vulnerability in Unraid that stems from insecure use of the PHP extract function. An attacker who can reach the affected interface may abuse it to run code with root privileges on the system. CISA notes that this issue is chainable with CVE-2020-5849 for initial access, which raises the stakes for any Unraid host exposed to untrusted networks. Defenders should treat it as a high-priority patching item and confirm exact scope against the vendor advisory.

How it works

The flaw involves insecure use of PHP’s extract function. In general terms, extract can pull attacker-controlled data into the current symbol table; when that data is not properly filtered or when it overwrites critical variables, the application can be tricked into executing unintended code. On Unraid this can result in remote code execution as root. Public detail on the precise call sites and request parameters is limited, so teams should rely on the vendor advisory rather than assuming a particular exploit path. Because the vulnerability can be chained with CVE-2020-5849, an attacker who first gains a foothold via the companion issue may then escalate or achieve reliable code execution through this one. No specific exploit mechanics or payloads are described here; any proof-of-concept material should be obtained only from trusted vendor or coordinated-disclosure sources.

Am I affected? How to find it in your systems

Unraid is commonly deployed as a NAS or home-lab / small-business storage platform, often running on dedicated hardware or virtual machines and exposing a web-based management interface. Inventory every host that presents an Unraid management UI, whether on the internal network or reachable from the internet. Check the installed Unraid version against the fixed releases listed in the vendor advisory; do not rely on version numbers stated elsewhere. Look for systems that still accept unauthenticated or weakly authenticated access to the web UI, and note any instances where the management port is reachable from untrusted segments.

For detection of possible exploitation, review web-server and application logs for anomalous requests that manipulate PHP variables or that coincide with unexpected process creation running as root. Endpoint or host-based telemetry that records new processes spawned by the web server user (or sudden privilege elevation to root) can also surface abuse. Because CWE detail is not supplied in the provided facts, treat any unusual extract-related or variable-injection patterns as suspicious and escalate for forensic review. Confirm all version and configuration checks directly with the vendor advisory before declaring a system clean.

How to remediate

Apply the updates published by the Unraid vendor exactly as instructed in their advisory. CISA’s required action is to apply updates per vendor instructions; that remains the primary remediation. After patching, verify that the management interface reports the expected fixed build and re-test access controls. Beyond the patch, harden the deployment: restrict the Unraid web UI to management networks or VPN-only access, enforce strong authentication, and disable any unnecessary services or plugins that enlarge the attack surface. Keep the underlying OS and PHP runtime current according to vendor guidance, and ensure that file-system and process integrity monitoring is enabled so future anomalies are visible.

If you can't patch immediately

If an immediate update is not possible, isolate the Unraid host from untrusted networks with strict firewall rules or network segmentation so that only authorized administrators can reach the management interface. Consider placing a reverse proxy or web application firewall in front of the UI to block anomalous request patterns associated with PHP variable injection, treating this as temporary virtual patching until the official update is applied. Disable any non-essential features or plugins that rely on the vulnerable code path if the vendor documentation permits it. Increase monitoring: alert on new root-owned processes spawned by the web stack, on unexpected outbound connections, and on authentication failures or unusual POSTs to the management endpoints. Document the compensating controls and set a firm deadline for completing the vendor update.

If your data may have been exposed

Actively exploited remote-code-execution vulnerabilities can lead to full host compromise and subsequent data theft or ransomware deployment; the facts supplied for this CVE do not document ransomware use, but the root-level impact still warrants assuming potential exposure if exploitation is confirmed. Preserve logs and disk images before remediation so incident responders can determine whether code execution occurred. Rotate credentials and secrets that resided on the affected system, and review file-share permissions and backup integrity. As a quick additional check, you can run a free exposure scan of your email addresses against known breach data sets to see whether related accounts have appeared in prior incidents.