CVE-2026-5027 — Langflow: unauthenticated path traversal to arbitrary file write, exploited in the wild
CVE-2026-5027 (CVSS 8.8, CWE-22) is a path-traversal flaw in Langflow — the widely deployed open-source low-code platform for building LLM pipelines, RAG systems and agentic workflows. The POST /api/v2/files endpoint fails to sanitise the filename parameter in multipart form data, allowing ../ sequences to write files to arbitrary filesystem locations (BleepingComputer, 2026-06-10). It is effectively pre-authentication: Langflow ships with LANGFLOW_AUTO_LOGIN enabled by default, so a single unauthenticated request obtains a valid session token before reaching the file-write primitive, which chains to code execution via webshell placement or .pth injection. Tenable discovered and disclosed the flaw on 27 March 2026 after two months of unsuccessful vendor contact (Tenable TRA-2026-26, 2026-03-27); VulnCheck subsequently observed active exploitation in honeypots, with attackers staging test files on victim systems, and Censys data shows roughly 7,000 publicly exposed instances. A patch is now available (Langflow 1.9.0 / langflow-base 0.8.3, with 1.10.0 released 10 June). Technique: T1190 Exploit Public-Facing Application → T1505.003 Web Shell.
CVE Summary Table
| CVE | Product | CVSS | EPSS | KEV | Exploited | Patch | Source |
|---|---|---|---|---|---|---|---|
| CVE-2026-5027 | Langflow (POST /api/v2/files) |
8.8 | n/a | No | Yes (VulnCheck) | 1.9.0 / 1.10.0 | BleepingComputer |
| CVE-2026-41089 | Windows Netlogon (Server 2012–2025) | 9.8 | n/a | No | Yes (CCB Belgium) | May 2026 Patch Tuesday | CERT-EU 2026-007 |
CVE-2026-41089 is carried as a § 4 update — see below; it is listed here for the consolidated vulnerability view.
CVE-2026-5027 (CVSS 8.8, CWE-22) is a path-traversal flaw in Langflow — the widely deployed open-source low-code platform for building LLM pipelines, RAG systems and agentic workflows.
Defender actions
- Patch Langflow (1.9.0 / 1.10.0) and disable auto-login (CVE-2026-5027). This pre-auth path-traversal-to-RCE is exploited in the wild with ~7,000 instances exposed. If patching is delayed, set
LANGFLOW_AUTO_LOGIN=false, remove the instance from internet exposure, and hunt web logs forPOST /api/v2/filesrequests containing../or%2e%2e%2f.
ATT&CK mapping
2 techniques mapped from the cited reporting · MITRE ATT&CK v19.1
Initial Access TA0001
T1190Exploit Public-Facing Application
Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network. The weakness in the system can be a software bug, a temporary glitch, or a misconfiguration.
Persistence TA0003
T1505.003Server Software Component: Web Shell
Adversaries may backdoor web servers with web shells to establish persistent access to systems. A Web shell is a Web script that is placed on an openly accessible Web server to allow an adversary to access the Web server as a gateway into a network. A Web shell may provide a set of functions to execute or a command-line interface on the system that hosts the Web server.
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