Vulnerability · Published Oct 16, 2026 · Assigned by GitHub_M
CVE-2026-96620Claude Agent SDK: Argument Injection via resume Option Allows Arbitrary Command Execution
Critical 9.2
In plain English
A critical-severity improper input validation in claude-agent-sdk-python from anthropics. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.7% (higher than 54% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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 packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| PyPI | claude-agent-sdk | 0.2.121 | GHSA-h4mw-j7qp-8mwm |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| anthropics | claude-agent-sdk-python | < 0.2.121 |
Weakness: CWE-20, CWE-78, CWE-88 · 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
References
- https://github.com/anthropics/claude-agent-sdk-python/security/advisories/GHSA-h4mw-j7qp-8mwm x_refsource_CONFIRM
- https://github.com/anthropics/claude-agent-sdk-python/pull/1123 x_refsource_MISC
- https://github.com/anthropics/claude-agent-sdk-python/commit/347a1cb88d7652199399db1b7f914e0a459a6662 x_refsource_MISC
- https://github.com/anthropics/claude-agent-sdk-python/releases/tag/v0.2.121 x_refsource_MISC