What’s Vulnerable › Vulnerabilities

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

• Severity: critical (CVSS 9.2 v4.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.7% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-10-16 · updated 2026-10-21
• Weakness: CWE-20

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.

Affected products

• anthropics claude-agent-sdk-python: before 0.2.121

References

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

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