CVE-2026-42471: MixPHP Framework RCE Vulnerability

CVE-2026-42471 Overview

CVE-2026-42471 is an unsafe deserialization vulnerability in the MixPHP Framework affecting versions 2.x through 2.2.17. The flaw resides in the sync-invoke client component, specifically at Connection.php:76, which calls unserialize() on data returned from the server response. A malicious server can deliver crafted serialized payloads that trigger PHP object instantiation chains, leading to client-side remote code execution. The issue is classified under [CWE-502] (Deserialization of Untrusted Data).

Critical Impact

Clients connecting to an attacker-controlled MixPHP sync-invoke server can be compromised through PHP object injection, resulting in arbitrary code execution within the client process.

Affected Products

• MixPHP Framework 2.x
• MixPHP Framework versions up to and including 2.2.17
• Applications using the sync-invoke client component

Discovery Timeline

• 2026-05-01 - CVE-2026-42471 published to NVD
• 2026-05-05 - Last updated in NVD database

Technical Details for CVE-2026-42471

Vulnerability Analysis

The vulnerability stems from unsafe handling of server responses in the MixPHP sync-invoke client. When the client issues a synchronous remote procedure call, it reads the raw response stream and passes the buffer directly to PHP's unserialize() function at Connection.php:76. PHP's native unserialize() reconstructs object graphs and invokes magic methods such as __wakeup(), __destruct(), and __toString() during deserialization. Attackers controlling the server can craft serialized payloads that abuse gadget chains in loaded classes to achieve arbitrary code execution on the client. The EPSS score is currently low, but the consequences of exploitation are severe given the resulting code execution context.

Root Cause

The root cause is the implicit trust the client places in the server response. The sync-invoke protocol assumes a benign, authenticated server endpoint, but performs no integrity validation, signing, or use of a safe serialization format before invoking unserialize(). Any client that connects to a malicious or compromised server inherits the server's ability to inject objects into the client's PHP runtime.

Attack Vector

Exploitation requires the victim client to connect to an attacker-controlled MixPHP sync-invoke server. Once connected, the server returns a crafted serialized PHP payload. The client deserializes the payload, instantiates attacker-chosen objects, and triggers gadget chain execution. The attack is network-based and unauthenticated from the client's perspective, but depends on the attacker positioning a malicious server or hijacking a legitimate one. Technical references are available in the MixPHP repository, the vulnerable Server.php source, and a public GitHub Gist demonstrating the issue.

The exploitation flow involves the client opening a TCP connection to the malicious server, the server responding with a serialized PHP object payload, and the client invoking unserialize() on that payload, which executes attacker-controlled gadget chains during object construction or destruction.

Detection Methods for CVE-2026-42471

Indicators of Compromise

• Outbound connections from PHP application hosts to unexpected or untrusted MixPHP sync-invoke endpoints.
• PHP worker processes spawning shell interpreters (sh, bash, cmd.exe) or unusual child processes following sync-invoke calls.
• Network traffic containing PHP serialized object markers such as O: or C: patterns directed at client processes.
• Unexpected file writes, cron entries, or outbound callbacks originating from PHP-FPM or CLI workers using MixPHP.

Detection Strategies

• Inspect application dependencies for MixPHP versions 2.x through 2.2.17 using composer manifests and lockfiles.
• Hunt for invocations of unserialize() on network-sourced data within MixPHP-based codebases.
• Use endpoint detection telemetry to correlate php process activity with anomalous child process creation and outbound network connections.

Monitoring Recommendations

• Log and alert on all outbound connections from PHP runtimes to non-allowlisted hosts and ports used for sync-invoke RPC.
• Monitor for new or modified PHP class autoload paths that could introduce gadget chains.
• Capture full process lineage for php and php-fpm to surface deserialization-driven code execution patterns.

How to Mitigate CVE-2026-42471

Immediate Actions Required

• Inventory all applications using MixPHP Framework 2.x and identify any sync-invoke clients in use.
• Restrict sync-invoke client connections to trusted, authenticated server endpoints under your control.
• Block egress from PHP application servers to arbitrary external hosts on sync-invoke ports.
• Review and audit any classes loaded in the client runtime that could serve as deserialization gadgets.

Patch Information

No official fixed version is referenced in the published advisory data at the time of writing. Monitor the MixPHP project repository for updates beyond version 2.2.17 that replace unserialize() with a safe serialization format such as JSON or msgpack, or that add cryptographic integrity checks on server responses.

Workarounds

• Replace direct calls to unserialize() in Connection.php with json_decode() or another safe format if the server protocol can be modified.
• Apply an allowed-classes filter via unserialize($data, ['allowed_classes' => false]) where feasible to neutralize object instantiation.
• Terminate sync-invoke usage entirely until a patched release is available, substituting an alternative RPC mechanism over signed or mutually authenticated channels.
• Enforce mutual TLS between sync-invoke clients and servers to prevent unauthorized servers from delivering payloads.

# Configuration example: enforce safe deserialization in PHP application code
# Replace vulnerable call:
#   $result = unserialize($response);
# With a hardened equivalent:
$result = unserialize($response, ['allowed_classes' => false]);

# Network-level egress restriction (iptables) limiting sync-invoke clients
# to a single trusted server:
iptables -A OUTPUT -p tcp -d 10.0.0.10 --dport 9503 -j ACCEPT
iptables -A OUTPUT -p tcp --dport 9503 -j REJECT