CVE-2026-8859 is a path traversal vulnerability (CWE-22) affecting IBM Langflow OSS versions 1.0.0 through 1.10.0. The vulnerability arises from improper input validation of filenames extracted from HTTP response Content-Disposition headers in the APIRequest component when the "Save to File" feature is enabled. An attacker controlling an external HTTP server can craft filenames containing path traversal sequences (e.g., ../) to write arbitrary files to unintended locations accessible by the Langflow process. This can lead to complete compromise of confidentiality, integrity, and availability of the affected system, as reflected by the CVSS 3.1 base score of 9.9.

Successful exploitation allows an attacker with network access and limited privileges (PR:L) to write arbitrary files to locations accessible by the Langflow process, potentially leading to full system compromise including confidentiality, integrity, and availability impacts. The vulnerability is remotely exploitable without user interaction and requires low attack complexity.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until a fix is available, it is recommended to disable the "Save to File" feature if possible and restrict network access to the Langflow OSS service to trusted sources only.