CVE-2026-10566: MetaGPT Deserialization Vulnerability

CVE-2026-10566 Overview

CVE-2026-10566 is an insecure deserialization vulnerability in FoundationAgents MetaGPT versions up to 0.8.2. The flaw resides in the Message.check_instruct_content function within metagpt/schema.py. Manipulating the mapping argument triggers unsafe deserialization during message validation. Exploitation requires local access and low-level privileges on the host running MetaGPT. A public exploit is available, but the project maintainers have not responded to the disclosure issue. The weakness is classified under CWE-20: Improper Input Validation.

Critical Impact
A local attacker with limited privileges can supply a crafted mapping argument to trigger deserialization, resulting in limited confidentiality, integrity, and availability impact within the MetaGPT process context.

Affected Products

FoundationAgents MetaGPT versions through 0.8.2
The metagpt/schema.py module exposing Message.check_instruct_content
Downstream agent workflows that pass attacker-controlled mapping data

Discovery Timeline

2026-06-02 - CVE-2026-10566 published to NVD
2026-06-02 - Last updated in NVD database

Technical Details for CVE-2026-10566

Vulnerability Analysis

MetaGPT is a multi-agent framework that orchestrates large language model (LLM) agents using structured message passing. The Message.check_instruct_content function in metagpt/schema.py validates instruction content by consuming a mapping argument supplied by callers. The function processes this argument through a deserialization path that does not constrain the resulting object types. An attacker who can influence the mapping value can supply a serialized payload that constructs unintended objects when deserialized. The flaw is categorized as [CWE-20] because input is not validated before it reaches the deserialization routine. The Exploit Prediction Scoring System (EPSS) reports a low probability of opportunistic exploitation, consistent with the local-only attack vector.

Root Cause

The root cause is improper input validation on the mapping parameter passed to Message.check_instruct_content. The function trusts caller-supplied data and routes it into a deserialization step without enforcing an allowlist of safe types or schema constraints. Any object reconstruction during deserialization executes within the MetaGPT process, inheriting its privileges.

Attack Vector

Exploitation requires local execution context on the system running MetaGPT. An attacker with low privileges crafts a malicious mapping payload and triggers a code path that invokes check_instruct_content. This may occur through agent input pipelines, persisted message stores, or local inter-process channels that feed messages into the framework. A public proof-of-concept referenced in the GitHub Issue Discussion demonstrates the manipulation.

No verified exploit code is published in a structured form. Refer to the VulDB Vulnerability Details and the GitHub PoC Repository for additional technical context.

Detection Methods for CVE-2026-10566

Indicators of Compromise

Unexpected Python objects materialized inside MetaGPT agent processes after message handling
Calls to Message.check_instruct_content with mapping payloads sourced from untrusted files or network inputs
Child processes spawned by the MetaGPT runtime that do not match normal agent activity

Detection Strategies

Instrument metagpt/schema.py to log the type and origin of mapping arguments reaching check_instruct_content
Apply runtime Python audit hooks (sys.addaudithook) to flag deserialization events triggered from the schema module
Correlate local user activity with MetaGPT process behavior to identify low-privileged users invoking agent workflows

Monitoring Recommendations

Track file access on serialized message stores used by MetaGPT for unauthorized modifications
Alert on MetaGPT processes invoking interpreters, shells, or network utilities outside their baseline
Forward Python application logs to a central data lake to support retrospective hunting for malicious mapping payloads

How to Mitigate CVE-2026-10566

Immediate Actions Required

Restrict local access to systems running MetaGPT to trusted operators only
Audit all callers of Message.check_instruct_content and reject mapping values from untrusted sources
Run MetaGPT under a dedicated low-privilege service account isolated from sensitive data

Patch Information

The maintainers have not published a security patch at the time of disclosure. The reporter notified the project through an issue without response. Track the GitHub Issue Discussion and the VulDB CVE Report for fix availability. Until a patched release ships, treat all versions up to and including 0.8.2 as vulnerable.

Workarounds

Replace unsafe deserialization with a strict schema validator such as pydantic models that reject unknown types
Wrap check_instruct_content calls with an allowlist of expected mapping keys and value types
Execute MetaGPT inside a container or sandbox that blocks outbound network access and limits filesystem writes
Remove or disable agent workflows that accept message inputs from untrusted local users

bash

# Configuration example: run MetaGPT as a confined service user
sudo useradd --system --shell /usr/sbin/nologin metagpt-svc
sudo chown -R metagpt-svc:metagpt-svc /opt/metagpt
sudo -u metagpt-svc python -m metagpt --config /opt/metagpt/config.yaml