---
id: "CVE-2026-48503"
kind: "vulnerability"
aliases: ["CVE-2026-48503"]
title: "libIEC61850: out-of-range MMS file read leaks stale connection buffer bytes"
severity: "high"
cvss: 7.5
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["c", "energy-sector", "iec-61850", "industrial-control-systems", "libiec61850", "package"]
not_affected_if: ["file-service-disabled", "version-1.6.2-or-later"]
published_at: "2026-10-16T16:18:11+00:00"
first_seen_at: "2026-10-23T21:57:13+00:00"
updated_at: "2026-10-25T03:25:02+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-48503", "first_seen_at": "2026-10-23T21:57:13+00:00"}]
---

# libIEC61850: out-of-range MMS file read leaks stale connection buffer bytes

libIEC61850 is an open-source IEC 61850 client and server library. Before 1.6.2, an out-of-range initialPosition in an MMS fileOpen request lets a remote client receive oversized file read responses that include stale bytes from a reused connection buffer.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Check the libIEC61850 version in use; versions before `1.6.2` are affected.
- Check whether the MMS file service is enabled in the server configuration (`unknown` for the exact setting name; the sources do not say).

## Fix

- Upgrade libIEC61850 to `1.6.2` or later.
- Disable the MMS file service if it is not needed (`unknown` for the exact setting; the sources do not say).

## Timeline

- 2026-10-23T21:57:13+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-48503

## From the sources

libIEC61850 is an open-source implementation of IEC 61850 client and server protocols including MMS, GOOSE, Sampled Values, and R-Session. Prior to 1.6.2, the MMS file service in src/mms/iso_mms/server/mms_file_service.c accepts an out-of-range initialPosition in fileOpen and stores it in the file-read state. The fileRead path then subtracts the larger read position from the file size using unsigned arithmetic and fails to limit the response to the actual FileSystem_readFile return value. The oversized response can include stale bytes from the reused connection buffer after the requested file contents, disclosing prior response data and protocol fragments to an unauthenticated remote client when the file service is enabled. This issue is fixed in version 1.6.2.

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_