CVE-2026-96620: CWE-20: Improper Input Validation in anthropics claude-agent-sdk-python
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.
CVSS v4.0
Score 9.2critical
Affected software
anthropics
claude-agent-sdk-python
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-09-23T14:35:50.128Z
- Cvss Version
- 4.0
- State
- PUBLISHED
Threat ID: 6ad283572cdf04f6562f6cef
Added to database: 10/16/2026, 20:04:39 UTC
Last updated: 10/16/2026, 20:04:39 UTC
Views: 1
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