CVE-2026-96620

critical

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.

References

https://github.com/anthropics/claude-agent-sdk-python/security/advisories/GHSA-h4mw-j7qp-8mwm

https://github.com/anthropics/claude-agent-sdk-python/releases/tag/v0.2.121

https://github.com/anthropics/claude-agent-sdk-python/pull/1123

https://github.com/anthropics/claude-agent-sdk-python/commit/347a1cb88d7652199399db1b7f914e0a459a6662

https://euvd.enisa.europa.eu/vulnerability/EUVD-2026-103155

Details

Source: Mitre, NVD

Published: 2026-10-16

Updated: 2026-10-16

Risk Information

CVSS v2

Base Score: 7.5

Vector: CVSS2#AV:N/AC:L/Au:N/C:P/I:P/A:P

Severity: High

CVSS v3

Base Score: 9.8

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Severity: Critical

CVSS v4

Base Score: 9.2

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

Severity: Critical