CVE-2026-27869: Teldat Regesta Smart HD-PLC DoS Flaw

CVE-2026-27869 Overview

CVE-2026-27869 is a denial of service vulnerability affecting the Teldat Regesta Smart HD-PLC industrial communications device. An unauthenticated remote attacker can exploit the web interface through a Slow Loris attack to exhaust available connection resources. The flaw stems from improper resource allocation without limits, classified as [CWE-770]. Successful exploitation renders the management web interface unreachable, disrupting administration of the affected device. The vulnerability requires no credentials and no user interaction.

Critical Impact
An unauthenticated network attacker can render the Regesta Smart HD-PLC web management interface unavailable by holding open partial HTTP connections, blocking legitimate administrative access.

Affected Products

Teldat Regesta Smart HD-PLC
Model TLDPH16D2 firmware version 11.02.05.10.02
Web management interface component

Discovery Timeline

2026-06-17 - CVE-2026-27869 published to NVD
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2026-27869

Vulnerability Analysis

The Regesta Smart HD-PLC web interface fails to enforce limits on concurrent connections or partial HTTP request lifetimes. An attacker establishes multiple TCP sessions to the HTTP service and sends incomplete request headers at a slow drip, never finishing the request. The server keeps these sockets open while waiting for the remainder of each request, eventually exhausting the connection pool.

Once the pool is saturated, legitimate operators cannot reach the management interface. The Slow Loris technique requires minimal bandwidth from the attacker because each connection only needs periodic byte transmission to remain alive. The CVSS 4.0 score of 6.9 reflects network-reachable, unauthenticated exploitation with availability impact limited to the management plane.

Root Cause

The root cause is allocation of resources without enforced limits ([CWE-770]) in the embedded HTTP server. The service does not impose per-client connection caps, per-request header timeouts, or aggregate concurrent connection ceilings. This permits a single attacker to monopolize the listener.

Attack Vector

The attack vector is network-based and requires no authentication. An adversary with TCP/IP reachability to the device web port can initiate the attack from any host on the same network segment or any routed network that exposes the interface. According to the EPSS data dated 2026-06-18, the exploitation probability stands at 0.524%. No public proof of concept or exploit code is currently catalogued in ExploitDB. Technical specifics are documented in the HackRTU CVE-2026-27869 Blog and HackRTU HRTU-0002 Blog.

No verified exploitation code is available. The Slow Loris technique itself is well documented in public security literature and relies on sending partial HTTP headers such as repeated X-a: b\r\n lines without terminating the request.

Detection Methods for CVE-2026-27869

Indicators of Compromise

Sustained high count of half-open or established TCP connections to the Regesta Smart HD-PLC web port from a single source IP
HTTP requests that never complete header transmission, observable as connections idle in the ESTABLISHED state with no final \r\n\r\n
Loss of administrative access to the device web interface while ICMP and other services remain responsive

Detection Strategies

Monitor concurrent connection counts to the device management interface and alert on thresholds that exceed normal operator activity
Inspect network flow telemetry for prolonged sessions with abnormally low byte counts directed at the HTTP port
Correlate failed administrative logon attempts with connection saturation events to identify availability disruptions

Monitoring Recommendations

Deploy network sensors at the boundary protecting industrial OT segments hosting Teldat devices and forward flow data to a centralized analytics platform
Baseline normal management traffic patterns for each Regesta Smart HD-PLC and alert on deviations
Track HTTP request completion ratios and average header transmission duration per source IP

How to Mitigate CVE-2026-27869

Immediate Actions Required

Restrict network access to the Regesta Smart HD-PLC web interface to a dedicated management VLAN or jump host using firewall ACLs
Place a reverse proxy or load balancer with Slow Loris protection in front of the management interface where deployment topology permits
Contact Teldat through the Teldat Support Portal to obtain remediation guidance for firmware 11.02.05.10.02

Patch Information

No vendor patch reference is published in the NVD entry for CVE-2026-27869 at the time of disclosure. Consult the Teldat Support Portal and the Teldat Installation Guide for the latest firmware availability and configuration hardening guidance for the Regesta Smart Nessum series.

Workarounds

Block inbound TCP connections to the device HTTP management port from untrusted networks at the perimeter firewall
Enforce per-source-IP connection rate limits using an upstream network device or reverse proxy
Disable the web management interface when not in active use and rely on out-of-band administrative channels where supported
Segment the affected device into a restricted OT zone with strict east-west traffic controls

bash

# Example iptables rule limiting concurrent HTTP connections per source IP
iptables -A INPUT -p tcp --dport 80 -m connlimit \
  --connlimit-above 10 --connlimit-mask 32 -j REJECT