CVE-2026-67873: lib60870-C Buffer Overflow Vulnerability

CVE-2026-67873 Overview

CVE-2026-67873 is a heap-based buffer overflow in lib60870-C version 2.4.0, an open-source implementation of the IEC 60870-5-101/104 protocols used in industrial control and SCADA environments. The flaw resides in the server-side FileSegment Application Service Data Unit (ASDU) encoding path. The FileSegment_encode() routine validates only the standalone segment length through FileSegment_GetMaxDataSize(). It does not verify the residual capacity of the current ASDU frame before writing object fields and segment data, allowing a write beyond the allocated buffer.

Critical Impact
A server encoding a FileSegment ASDU can overflow the heap buffer backing the frame, corrupting adjacent memory and destabilizing IEC 60870-5 SCADA endpoints.

Affected Products

lib60870-C version 2.4.0
Applications and gateways embedding lib60870-C 2.4.0 as an IEC 60870-5-104 server
SCADA and telecontrol components using the affected FileSegment encoding path

Discovery Timeline

2026-08-06 - CVE-2026-67873 published to the National Vulnerability Database
2026-08-06 - Last updated in NVD database

Technical Details for CVE-2026-67873

Vulnerability Analysis

The lib60870-C library encodes IEC 60870-5 telecontrol messages into ASDU frames written to a fixed-capacity heap buffer. When a server transmits file data, it constructs FileSegment ASDUs that carry object fields followed by the raw segment payload. The encoder queries FileSegment_GetMaxDataSize() to determine the maximum standalone segment length. That value reflects only the theoretical limit for a segment in isolation. It does not account for bytes already consumed by prior information objects or the current ASDU header in the frame.

When the encoder writes the object identifier fields and segment data, it advances the buffer pointer past the end of the underlying heap allocation. Adjacent heap metadata and allocations are corrupted. The classification is a heap-based buffer overflow [CWE-122].

Root Cause

The root cause is missing residual-capacity validation in FileSegment_encode(). The code checks the segment size against the protocol maximum rather than against the remaining space in the destination frame buffer. This is a boundary condition error where the writer trusts a protocol-derived length instead of the actual buffer state.

Attack Vector

The defect lives on the server-side encoding path. An attacker or misconfigured peer that induces the server into transmitting a FileSegment ASDU under conditions where the ASDU frame is already partially filled can trigger the overflow. Depending on heap layout, consequences range from process crash and denial of service on the SCADA endpoint to potential memory corruption affecting neighboring allocations. Exploitation feasibility beyond denial of service depends on the host allocator and adjacent objects.

No verified exploit code is public. Technical details are tracked in GitHub Issue #201 on the lib60870 repository.

Detection Methods for CVE-2026-67873

Indicators of Compromise

Unexpected termination or restart of processes linking lib60870-C on IEC 60870-5-104 servers
Heap corruption signatures in core dumps referencing FileSegment_encode or ASDU frame buffers
Malformed or oversized FileSegment ASDUs observed in IEC 60870-5-104 packet captures on TCP port 2404

Detection Strategies

Inventory binaries and firmware images for lib60870-C 2.4.0 using software composition analysis against the lib60870 v2.4.0 release
Deploy IEC 60870-5-104 protocol inspection to flag file transfer sequences with anomalous segment counts or lengths
Monitor SCADA hosts for abnormal crash telemetry, segmentation faults, and glibc heap assertion messages tied to control-system processes

Monitoring Recommendations

Enable process and crash telemetry collection on servers and gateways that terminate IEC 60870-5-104 sessions
Baseline normal file transfer patterns on control networks and alert on deviations in ASDU type identifiers 120–127
Correlate protocol anomalies with endpoint stability events to surface early-stage exploitation attempts

How to Mitigate CVE-2026-67873

Immediate Actions Required

Identify every deployment that ships or statically links lib60870-C 2.4.0 in server mode
Restrict inbound access to IEC 60870-5-104 TCP port 2404 to authenticated peers on segmented control networks
Disable or block file transfer ASDUs on control links where they are not operationally required
Track upstream fixes in the lib60870 repository and monitor Issue #201

Patch Information

At time of publication, no fixed release is referenced in the enriched CVE data. Consult the lib60870 releases page and the maintainer tracker for updated versions. Until a patched build is available, apply the workarounds below and rebuild affected products against corrected source once released.

Workarounds

Add a residual-capacity check in FileSegment_encode() that verifies the object fields plus segment payload fit within the remaining ASDU frame before writing
Cap the effective segment size to the minimum of FileSegment_GetMaxDataSize() and the frame's remaining free bytes
Enforce network segmentation and firewall rules that permit IEC 60870-5-104 traffic only between known control endpoints
Deploy protocol-aware intrusion detection to reject malformed file transfer sequences on the wire

bash

# Example firewall restriction limiting IEC 60870-5-104 to trusted control peers
iptables -A INPUT -p tcp --dport 2404 -s 10.20.30.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 2404 -j DROP