nanoMODBUS Server-Side Out-of-Bounds Write in handle_read_file_record() (CVE-2026-71254) | HOL Guard CVE

Critical · CVSS 9.8CVE-2026-71254

nanoMODBUS Server-Side Out-of-Bounds Write in handle_read_file_record()

Answer in brief

CVE-2026-71254 records a Critical severity (CVSS 9.8) vulnerability in nanoMODBUS Server-Side Out-of-Bounds Write in handle_read_file_record(). The current sources do not mark it as known exploited. The current feed maps debevv/nanoMODBUS (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Aug 5, 2026Updated Aug 26, 2026Source checked Sep 20, 2026First seen by HOL Aug 5, 2026Material review Aug 26, 2026

Upstream Advisory

Key facts

Risk: Critical · CVSS 9.8
Exploitation: Not marked as known exploited
Affected software: 1 mapped package or product
Fix availability: Not reported

Why this deserves its current priority

CVSS is 9.8. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps debevv/nanoMODBUS (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
debevv/nanoMODBUSgeneric	0	Not reported

Recommended response

Check inventory. Check lockfiles and deployed manifests for debevv/nanoMODBUS.
Review the reported fix. Monitor this advisory for an available fix and review any installs of the affected package.

Evidence timeline and material changes

Published upstream
Aug 5, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Aug 26, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Aug 5, 2026

Sources and claim methodology

Upstream source description

nanoMODBUS through v1.23.0 contains an out-of-bounds write in the Modbus server-side handle_read_file_record function (FC 0x14, Read File Record) in nanomodbus.c. The function validates that the total request size does not exceed 245 bytes and that each sub-request's record_length is at most 124, but it never validates the CUMULATIVE response size across all sub-requests before processing them.

Quoted source text, attributed separately from HOL analysis.