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.
Fix
Nothing published yet: no patch, vendor advisory or mitigation reference on NVD, no vendor advisory in the News for this CVE, not in CISA's KEV, no fixed package version. BaselineWatch does not guess at one.
Change history 5
- StatusAwaiting Analysis → PublishedNVD modified 2026-10-21 21:28
- StatusPublished → Awaiting AnalysisNVD modified 2026-10-21 22:16
- StatusAwaiting Analysis → PublishedNVD modified 2026-10-21 21:28
- StatusReceived → Awaiting AnalysisNVD modified 2026-10-19 21:13
- First seenCVSS 9.2NVD modified 2026-10-16 20:18
Affected (CPE criteria) 0
NVD has not attached CPE configurations yet.
References 4
- 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