CVE-2026-96620

Published Oct 16, 2026 Modified Oct 21, 2026 CWE-20 CWE-78 CWE-88

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.

Is your site exposed to CVE-2026-96620?

Run a free security scan — no signup, results in seconds.

EPSS — Exploit Prediction

0.0071
Probability of exploitation
0.54%
Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-20 Improper Input Validation
CWE-78 OS Command Injection
CWE-88 CWE-88

References

Frequently Asked Questions

What is CVE-2026-96620? +
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.
How do I check if I'm vulnerable to CVE-2026-96620? +
You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

Related Vulnerabilities

Don't wait for an exploit

Scan your website for vulnerabilities like CVE-2026-96620 — free, no signup required.

Patch and protect

Block known exploits with a web application firewall while you patch, keep your own devices clean, or test the fix on a fresh server.

Compare VPS prices →

Affiliate links: we may earn a commission, your price stays the same.