CVE-2026-102073

Executive Summary

CVE-2026-102073 is an unauthenticated, remotely exploitable improper input validation vulnerability (CWE-191) in the web service of Siemens APOGEE and TALON building automation controllers. A remote attacker can read portions of device memory or trigger a denial-of-service condition without authentication, yielding a high confidentiality impact per the CVSS vector (C:H/A:L), with a base score of 8.2. Because these devices operate in building management and OT/ICS environments, exploitation can expose sensitive memory contents and disrupt physical control systems that depend on continuous controller availability.

Technical Analysis

The vulnerability resides in the product web service, which, per the NVD description, "does not properly validate the length of user-controllable input." This is classified under CWE-191 (Integer Underflow). The combination of a length-validation failure and the integer-underflow classification indicates that a length value derived from attacker-supplied input is processed in a way that allows the computed or assumed buffer boundary to be smaller than the true boundary, enabling out-of-bounds read and, in some trigger conditions, a crash that produces a denial-of-service condition.

Two distinct impact primitives are documented:

1. Out-of-bounds memory read — the improper length handling allows the web service to return or process data beyond the intended input buffer, leaking portions of device memory to the remote requester (unauthenticated read).
2. Denial of service — malformed or oversized input can destabilize the web service, causing the controller to become unavailable (availability impact rated Low in the CVSS vector).

The attack surface is the controller web service, reachable over the network (AV:N) with no authentication (PR:N), no user interaction (UI:N), and low attack complexity (AC:L). The affected product families are Siemens APOGEE MBC (PPC), APOGEE MEC (PPC), APOGEE PXC Compact, APOGEE PXC Modular, and TALON TC Compact/Modular, in both BACnet and P2 Ethernet variants. Notably, for the MBC and MEC (PPC) lines, all versions are listed as affected — implying no fixed version has been documented for those models at this time. The PXC and TALON BACnet lines are fixed at V3.5.7, and the PXC/TALON P2 Ethernet lines at V2.8.21.

Because the vulnerability class involves improper length validation in a network-facing service, exploitation does not require credentials, a session, or any prior foothold beyond network reachability to the service.

Exploitation Scenarios

No public proof-of-concept, exploit code, or Nuclei template is available for CVE-2026-102073. The attack chain below is inferred strictly from the vulnerability class (improper length validation / integer underflow) and the NVD description. No specific function names, endpoints, parameters, or payload byte sequences are documented, and none are fabricated here.

1. Reconnaissance / target identification. An attacker scans for exposed Siemens APOGEE/TALON controllers using network discovery of the BACnet service (UDP/47808) and/or the product web service (HTTP/HTTPS). Shodan queries such as port:47808, product:"Siemens APOGEE", or http.title:"APOGEE" can identify internet- or flat-network-reachable devices. Because these run on OT networks, reachability may be obtained through a compromised IT host that has routing into the building control segment.

2. Triggering the flaw class. The attacker sends a request to the controller web service containing a user-controllable input whose declared length value is crafted to be inconsistent with the actual data or to underflow (e.g., a length field at or below the lower boundary). The web service fails to validate that length correctly, so processing proceeds against an incorrect boundary rather than rejecting the input.

3. Payload / execution method. At the vulnerability-class level, the malformed length causes the service to operate outside its intended buffer. This yields either an out-of-bounds read — potentially returning memory contents to the requester — or a fault/crash of the web service. No specific payload syntax is documented; the exact byte-level triggering input is unknown and no PoC is public.

4. Post-exploitation impact. Successful read leakage can expose device memory (potentially configuration data, credentials, or operational state), while the DoS primitive can take the controller's web service offline, disrupting supervisory monitoring and control of the HVAC/building systems it governs. The unauthenticated nature of the attack means it can be launched repeatedly and at scale across an exposed controller fleet.

Impact Assessment

The CVSS v3.1 base score is 8.2 (High) with vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:L:

• Confidentiality: High — the primary impact is unauthenticated disclosure of device memory contents via the out-of-bounds read.
• Availability: Low — a DoS condition is possible but is bounded (single-service degradation rather than full-system loss).
• Integrity: None — no integrity impact is documented for this vulnerability.
• Scope: Unchanged — impact is confined to the affected controller.

Affected systems: Siemens APOGEE MBC (PPC), APOGEE MEC (PPC), APOGEE PXC Compact, APOGEE PXC Modular, and TALON TC Compact/Modular controllers in both BACnet and P2 Ethernet configurations. These are building automation and control devices.

Business impact/blast radius: These controllers are embedded in critical facility infrastructure — HVAC, energy management, and building automation. Memory disclosure can leak sensitive device or configuration data; a DoS can degrade building operations, environmental control, and safety-relevant environmental systems. The affected PXC/TALON lines combine both exposure types in a single vulnerable service. The fact that MBC/MEC (PPC) lines list all versions as affected means the blast radius for those models cannot currently be bounded by an upgrade path.

Detection Guidance

Note: The rules below are generic detections for improper length validation / overlong-input attacks against HTTP-exposed controller web services. They are behavioral heuristics, not signatures for a known CVE-specific payload, since no public PoC or exploit data exists. Tune thresholds and paths to the actual APOGEE/TALON deployment.

Sigma Rule

title: Potential Improper Length Validation Attack Against Siemens APOGEE/TALON Web Service
id: 8f7c1a20-3b6d-4f9e-9c21-0d5e2b7a4c11
status: experimental
description: Detects requests to Siemens APOGEE/TALON controller web services with abnormal or overlong inputs, consistent with length-validation / integer-underflow exploitation (CVE-2026-102073).
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-102073
author: valtersit.com
date: 2026/01/01
logsource:
  category: webserver
detection:
  selection_method:
    cs-method:
      - GET
      - POST
  selection_status:
    sc-status:
      - 400
      - 500
      - 502
  selection_anomaly:
    - cs-uri-query|re: '(len|length|size|count)=(-|[0-9]{6,})'
    - cs-uri-query|len: '> 2000'
    - cs-uri-stem|len: '> 1024'
  condition: selection_method and (selection_anomaly or (selection_status and selection_anomaly))
fields:
  - c-ip
  - cs-method
  - cs-uri-stem
  - cs-uri-query
  - sc-status
falsepositives:
  - Legitimate management clients sending large configuration uploads
  - Vulnerability scanners generating malformed requests
level: medium

YARA Rule

rule CVE_2026_102073_APOGEE_Length_Abuse_HTTP
{
    meta:
        description = "Heuristic detection of HTTP request patterns potentially abusing length validation in Siemens APOGEE/TALON web services (CVE-2026-102073)"
        author = "valtersit.com"
        date = "2026-01-01"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-102073"
        cve = "CVE-2026-102073"

    strings:
        $m_get  = "GET /" ascii nocase
        $m_post = "POST /" ascii nocase
        $len1 = "len=" ascii nocase
        $len2 = "length=" ascii nocase
        $len3 = "size=" ascii nocase
        $len4 = "count=" ascii nocase
        $neg  = "=-" ascii
        $big  = "=999999" ascii

    condition:
        filesize < 10KB and
        ($m_get or $m_post) and
        any of ($len*) and
        ($neg or $big)
}

Suricata IDS Rule

alert http any any -> any any (msg:"CVE-2026-102073 Siemens APOGEE/TALON length validation abuse attempt"; flow:established,to_server; http.method; content:"GET"; http.method; content:"POST"; http.uri; pcre:"/(len|length|size|count)=(-|\d{6,})/i"; threshold:type both, track by_src, count 10, seconds 60; classtype:attempted-recon; reference:cve,2026-102073; reference:url,nvd.nist.gov/vuln/detail/CVE-2026-102073; sid:2026102073; rev:1;)

Elastic Detection

sequence by source.ip with maxspan=1m
  [network where network.transport == "tcp" and destination.port in (80, 443, 8080)]
  [http where http.request.method in ("GET", "POST") and
        (http.request.uri :~ ".*(len|length|size|count)=(-|[0-9]{6,}).*" or
         length(http.request.body.content) > 4096)]

Splunk SPL Query

index=web OR index=proxy (sourcetype=access_combined OR sourcetype=bluecoat OR sourcetype=pan:traffic)
| eval uri=coalesce(uri, cs_uri_stem, url)
| eval qs=coalesce(uri_query, cs_uri_query, cs_uri_query)
| eval status=coalesce(status, sc_status)
| where match(qs, "(?i)(len|length|size|count)=(-|[0-9]{6,})") OR len(qs) > 2000
| stats count min(_time) as first_seen max(_time) as last_seen values(status) as statuses by src_ip, dest_ip, uri
| where count > 5
| convert ctime(first_seen) ctime(last_seen)
| sort - count

Wazuh OSSEC Rule

<group name="web,apogee,cve_2026_102073,">
  <rule id="100773" level="10">
    <decoded_as>web-accesslog</decoded_as>
    <match>len=|length=|size=|count=</match>
    <regex>(len|length|size|count)=(-|\d{6,})</regex>
    <description>CVE-2026-102073: Potential improper length validation abuse against Siemens APOGEE/TALON web service</description>
    <mitre>
      <id>T1190</id>
    </mitre>
    <group>attack,web_attack,</group>
  </rule>

  <rule id="100774" level="12">
    <if_sid>100773</if_sid>
    <regex>HTTP/\d\.\d" (400|500|502) </regex>
    <description>CVE-2026-102073: Length-validation abuse resulting in web service error (possible DoS trigger)</description>
    <mitre>
      <id>T1190</id>
      <id>T1499</id>
    </mitre>
    <group>attack,web_attack,</group>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 0/4 — UNPATCHED. No patch evidence from any tracked source. Vendor fix is listed as N/A; no workarounds are provided; the OSV packages field is empty. Fixed-version thresholds exist for some product lines per the NVD description (BACnet lines: V3.5.7; P2 Ethernet lines: V2.8.21), but this is not confirmed as patch evidence by any tracked source and MBC/MEC (PPC) lines list all versions as affected.

1. Immediate mitigations

   • Do not expose APOGEE/TALON controller web services or BACnet (UDP/47808) interfaces directly to untrusted networks or the internet. Enforce network segmentation between IT and building automation/OT segments.
   • Restrict access to the controller web service to management jump hosts via firewall allowlists and ACLs.
   • Monitor for the anomalous request patterns described in the Detection Guidance section and alert on repeated 4xx/5xx responses from controller services.
   • Where feasible, disable the web service on controllers that do not require it.

2. Patch / upgrade steps

   • Contact Siemens customer support / the Siemens ProductCERT channel to confirm whether fixed firmware is available for each affected model. Per the NVD description, BACnet-based PXC Compact/Modular and TALON TC lines reference a fixed threshold of V3.5.7, and P2 Ethernet PXC/TALON lines reference V2.8.21; verify applicability before upgrade.
   • For APOGEE MBC (PPC) and MEC (PPC) lines, no fixed version is documented — assume these remain vulnerable and apply compensating network controls.
   • Stage firmware upgrades during maintenance windows and validate controller operation afterward.

3. Long-term hardening

   • Maintain a full inventory of building automation controllers with firmware versions tracked against vendor advisories.
   • Implement defense-in-depth for OT: unidirectional gateways or data diodes for telemetry, least-privilege network access, and continuous OT monitoring.
   • Subscribe to Siemens ProductCERT and ICS-CERT advisories; re-evaluate patch status as vendor information emerges, given the current UNPATCHED confidence rating.

References

• NVD — CVE-2026-102073: https://nvd.nist.gov/vuln/detail/CVE-2026-102073
• CWE-191 (Integer Underflow): https://cwe.mitre.org/data/definitions/191.html
• MITRE ATT&CK T1190 — Exploit Public-Facing Application: https://attack.mitre.org/techniques/T1190/
• Siemens ProductCERT / Siemens Security Advisories: https://www.siemens.com/cert
• CISA ICS Advisories (monitor for companion advisory covering these controller lines): https://www.cisa.gov/news-events/ics-advisories

Exploit-in-the-wild / threat actor evidence: None documented. CVE-2026-102073 is not listed in CISA KEV, has no public PoC or exploit code, no Nuclei template, and no reported exploitation campaigns. EPSS has not yet been scored by FIRST.org.