Security Bulletin
Summary
Langflow contains multiple vulnerabilities in its authentication, authorization, and network request controls across several API surfaces. The MCP project authentication function omits the default auth_type=none value from the set of modes requiring an API key, causing unauthenticated callers to be resolved as the system superuser on Streamable-HTTP and SSE-message transports when MCP Composer is enabled, representing an incomplete fix of a prior remediation. The public flow-build endpoint accepts an unvalidated files parameter that is forwarded directly to the storage backend, where the traversal payload is routed through the unvalidated flow_id storage segment, bypassing the existing path-containment guard and allowing unauthenticated arbitrary file reads. Deprecated build endpoints remain fully routed but lack the object-level ownership check present on the modern equivalent endpoint, permitting any authenticated user to enumerate and execute another tenant's private flow components and read flow-embedded values. The public flow metadata endpoint exposes the owner user_id, which can be reused as an anonymous client_id to collide with the owner's virtual session namespace, enabling an unauthenticated attacker to read and inject messages into another user's public-playground chat history. The unified model instantiation path constructs provider SDK clients such as ChatOllama and ChatOpenAI using tenant-controlled base URLs without invoking the connector SSRF validation guard, allowing an authenticated user to direct server-side HTTP requests to loopback, internal, or cloud-metadata endpoints even when connector SSRF protection is enabled.
Vulnerability Details
CVEID: CVE-2026-18899
DESCRIPTION: Langflow OSS could allow a remote attacker to read arbitrary files due to path traversal.
CWE: CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
CVSS Source: IBM
CVSS Base score: 7.5
CVSS Vector: (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N)
CVEID: CVE-2026-18891
DESCRIPTION: Langflow OSS could allow a remote attacker to execute arbitrary flows and access sensitive information due to improper authentication.
CWE: CWE-287: Improper Authentication
CVSS Source: IBM
CVSS Base score: 8.2
CVSS Vector: (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N)
CVEID: CVE-2026-18904
DESCRIPTION: Langflow OSS could allow a remote attacker to obtain sensitive information and inject unauthorized messages due to a namespace collision between user identifiers.
CWE: CWE-639: Authorization Bypass Through User-Controlled Key
CVSS Source: IBM
CVSS Base score: 8.2
CVSS Vector: (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N)
CVEID: CVE-2026-19294
DESCRIPTION: Langflow OSS could allow a remote authenticated attacker to execute and read any user's private flow due to improper authorization.
CWE: CWE-639: Authorization Bypass Through User-Controlled Key
CVSS Source: IBM
CVSS Base score: 6.4
CVSS Vector: (CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N)
CVEID: CVE-2026-18545
DESCRIPTION: Langflow is vulnerable to server-side request forgery (SSRF). This may allow an authenticated attacker to send unauthorized requests from the system, potentially leading to network enumeration or facilitating other attacks.
CWE: CWE-918: Server-Side Request Forgery (SSRF)
CVSS Source: IBM
CVSS Base score: 4.3
CVSS Vector: (CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N)
Affected Products and Versions
| Affected Product(s) | Version(s) |
| Langflow OSS | 1.0.0-1.11.1 |
Remediation/Fixes
IBM strongly recommends addressing the vulnerability now by upgrading Langflow OSS to version 1.11.2
Workarounds and Mitigations
None
Get Notified about Future Security Bulletins
References
Acknowledgement
Change History
21 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:
24 August 2026
Initial Publish date:
21 August 2026
UID
ibm17284579