Security Bulletin
Summary
Langflow contains two vulnerabilities affecting client-side security and access control integrity. The MarkdownField component renders chat messages using the rehypeRaw plugin without a sanitization pass, causing attacker-controlled LLM response text containing raw HTML to be inserted directly into the browser DOM; a stored cross-site scripting payload delivered through a Langflow flow can steal session tokens of any user who views the conversation, and when the victim is a superuser the attacker can chain this to remote code execution via the flow-build code execution path. The MCP configuration installation endpoint enforces a local-only access restriction using a client IP helper that blindly trusts the X-Forwarded-For header without validating that the request originated from a trusted proxy; any authenticated remote attacker can spoof this header to bypass the restriction and write or modify sensitive MCP configuration files on the server filesystem from a remote network location.
Vulnerability Details
CVEID: CVE-2026-8447
DESCRIPTION: Langflow OSS suffer from a stored cross-site scripting vulnerability in the Playground chat interface.
CWE: CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
CVSS Source: IBM
CVSS Base score: 6.1
CVSS Vector: (CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N)
CVEID: CVE-2026-9186
DESCRIPTION: Langflow OSS allows remote authenticated attackers to bypass localhost-only MCP configuration installation by spoofing X-Forwarded-For: 127.0.0.1 header, enabling arbitrary writes to IDE config files (~/.cursor/mcp.json, etc.).
CWE: CWE-284: Improper Access Control
CVSS Source: IBM
CVSS Base score: 6.5
CVSS Vector: (CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N)
Affected Products and Versions
| Affected Product(s) | Version(s) |
| Langflow OSS | 1.0.0-1.11.2 |
Remediation/Fixes
IBM strongly recommends addressing the vulnerability now by upgrading Langflow OSS to version 1.11.3
Workarounds and Mitigations
None
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References
Acknowledgement
odgrso GMO CyberSecurity by Ierae inc, Edward-x (YLChen-007)
Change History
28 Aug 2026: Initial Publication
*The CVSS Environment Score is customer environment specific and will ultimately impact the Overall CVSS Score. Customers can evaluate the impact of this vulnerability in their environments by accessing the links in the Reference section of this Security Bulletin.
Disclaimer
According to the Forum of Incident Response and Security Teams (FIRST), the Common Vulnerability Scoring System (CVSS) is an "industry open standard designed to convey vulnerability severity and help to determine urgency and priority of response." IBM PROVIDES THE CVSS SCORES ""AS IS"" WITHOUT WARRANTY OF ANY KIND, INCLUDING THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. CUSTOMERS ARE RESPONSIBLE FOR ASSESSING THE IMPACT OF ANY ACTUAL OR POTENTIAL SECURITY VULNERABILITY. In addition to other efforts to address potential vulnerabilities, IBM periodically updates the record of components contained in our product offerings. As part of that effort, if IBM identifies previously unidentified packages in a product/service inventory, we address relevant vulnerabilities regardless of CVE date. Inclusion of an older CVEID does not demonstrate that the referenced product has been used by IBM since that date, nor that IBM was aware of a vulnerability as of that date. We are making clients aware of relevant vulnerabilities as we become aware of them. "Affected Products and Versions" referenced in IBM Security Bulletins are intended to be only products and versions that are supported by IBM and have not passed their end-of-support or warranty date. Thus, failure to reference unsupported or extended-support products and versions in this Security Bulletin does not constitute a determination by IBM that they are unaffected by the vulnerability. Reference to one or more unsupported versions in this Security Bulletin shall not create an obligation for IBM to provide fixes for any unsupported or extended-support products or versions.
Document Location
Worldwide
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Document Information
Modified date:
28 August 2026
Initial Publish date:
28 August 2026
UID
ibm17285646