EUVD-2026-43116
GHSA-gx73-gv82-355v
Severity by source
CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Network-reachable web UI with low complexity but requires an authenticated account (PR:L); arbitrary file write leading to code execution yields high C/I/A with no scope change to a separate system.
Primary rating from Vendor (icscert).
CVSS VectorVendor: icscert
Lifecycle Timeline
6DescriptionCVE.org
OpenPLC Runtime v3 contains an authenticated arbitrary file write vulnerability in the legacy web UI program‑upload workflow. The application stores an attacker‑supplied filename (prog_file) directly into the Programs.File database field and later uses this value as the destination path for an uploaded file without validating or restricting the path. Because Python os.path.join() honors attacker‑controlled absolute paths, an authenticated user can write arbitrary files anywhere writable by the OpenPLC webserver process. In the default build pipeline, all C++ source files within the OpenPLC runtime core directory are automatically compiled into the executable runtime binary. By writing a malicious .cpp file into this directory, an authenticated attacker can escalate the arbitrary file write into arbitrary native code execution when the operator triggers a normal program compilation and runtime start.
Articles & Coverage 1
AnalysisAI
Authenticated arbitrary file write in OpenPLC Runtime v3 lets a logged-in user of the legacy web UI escalate to native code execution on the host running the automation controller. The program-upload workflow stores the attacker-supplied prog_file filename in the Programs.File database field and later reuses it unvalidated as a destination path; because Python os.path.join() honors absolute paths, files can be written anywhere the webserver process can write. Reported by ICS-CERT (CISA ICS advisory ICSA-26-190-01); no public exploit identified at time of analysis and it is not listed in CISA KEV.
Technical ContextAI
OpenPLC is an open-source Programmable Logic Controller (PLC) software stack used in ICS/OT lab, research, and small automation deployments; the Runtime v3 component is a Python web application that manages control programs and compiles a C++ runtime core into an executable binary. The root cause is CWE-73 (External Control of File Name or Path): the application trusts the client-supplied filename for an uploaded program and passes it to os.path.join() as the write destination. Python's os.path.join() has the well-known property that an absolute path argument discards all preceding path components, so an attacker-controlled absolute path fully overrides the intended upload directory. Because the default OpenPLC build pipeline compiles every .cpp file found in the runtime core source directory into the runtime binary, a file-write primitive into that directory becomes a code-execution primitive the next time the operator compiles and starts a program.
RemediationAI
No vendor-released patch is identified at time of analysis, so consult the CISA ICS advisory (https://www.cisa.gov/news-events/ics-advisories/icsa-26-190-01) and its CSAF file for the fixed release and apply it once published, citing the exact version from that advisory rather than any assumed number. Until then, apply specific compensating controls: restrict web-UI access to trusted operators and replace default/weak credentials so the PR:L barrier is meaningful (trade-off: minimal, this is baseline hygiene); place the OpenPLC web interface behind network segmentation or a VPN and block external access to its HTTP port so the network vector cannot be reached from untrusted networks (trade-off: remote engineers must use the VPN); run the webserver process under a low-privilege account and make the runtime core source directory read-only or owned by a separate build user so the file write cannot reach compilable .cpp locations (trade-off: may require adjusting the compile workflow); and monitor the runtime core directory and Programs upload path for unexpected file creation to detect exploitation attempts.
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Same weakness CWE-73 – External Control of File Name or Path
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External POC / Exploit Code
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