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CVE-2026-12940 – Unauthenticated RCE – IBM Langflow OSS 1.0.0–1.10.1

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Summary

CVE-2026-12940 is a critical unauthenticated remote code execution (RCE) vulnerability affecting IBM Langflow OSS versions 1.0.0 through 1.10.1. The flaw resides in the Model Context Protocol (MCP) stdio launcher, where an incomplete blocklist of dangerous environment variables allows a remote, unauthenticated attacker to inject OS commands and execute arbitrary code on the host. It carries a CVSS v3.1 base score of 9.8 (Critical).

Technical details

  • Root cause: The DANGEROUS_ENV_VARS blocklist defined in src/lfx/src/lfx/base/mcp/util.py omits the SHELLOPTS, BASHOPTS, and PS4 Bash environment variables. These variables are interpreted by the shell at process startup and can be weaponized to inject arbitrary commands that execute when the MCP stdio subprocess is spawned.
  • Trigger conditions: An attacker submits an HTTP request that causes the server to launch an MCP stdio subprocess with attacker-controlled environment variables. No authentication, credentials, or victim interaction are required.
  • Attack vector: Network-accessible; exploitable against any internet-facing Langflow OSS instance without prior access.
  • Impact: Full unauthenticated remote code execution on the underlying server — complete compromise of confidentiality, integrity, and availability.
  • CWE: CWE-78 (Improper Neutralization of Special Elements used in an OS Command).

Affected software

  • IBM Langflow OSS 1.0.0 through 1.10.1 (inclusive)

Severity

  • CVSS v3.1 Base Score: 9.8 (Critical)
  • Vector String: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Mitigation and recommended actions

  • Immediate — patch: Upgrade to Langflow OSS 1.10.2, released by IBM and available via PyPI. This version adds SHELLOPTS, BASHOPTS, and PS4 to the DANGEROUS_ENV_VARS blocklist, closing the injection path.
  • No documented vendor workaround exists for unpatched versions. Organizations unable to patch immediately should restrict network access to the Langflow web interface (default port 7860) at the perimeter, ensuring it is not reachable from untrusted networks.

IONIX Status

The IONIX research team is tracking ongoing exploitation attempts and recommends immediate patching. Potentially affected assets are outlined in this post.

References

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Map your entire attack surface (continously)

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