CVE-2026-102076

Executive Summary

CVE-2026-102076 is an unauthenticated remote denial-of-service vulnerability in the web service of Siemens APOGEE and TALON building automation controllers, caused by improper validation of user-supplied input during code upload (CWE-121, stack-based buffer overflow). It affects all versions of APOGEE MBC/MEC and versions of APOGEE PXC and TALON TC controllers below the fixed BACnet (V3.5.7) and P2 Ethernet (V2.8.21) releases, with a CVSS base score of 7.5. Because exploitation requires no authentication or user interaction and results in a full availability impact, internet- or network-exposed controllers are at high risk of disruption to building management, HVAC, and physical access control functions.

Technical Analysis

The vulnerability resides in the affected product's web service and is classified as CWE-121 (Stack-based Buffer Overflow). According to the NVD description, the web service "does not properly validate user-supplied input in upload code." This indicates that an HTTP-exposed upload routine accepts input without adequate length or content validation, allowing an attacker to supply data that overflows a stack-allocated buffer.

Two characteristics define the attack surface and severity:

• Unauthenticated reachability (PR:N, UI:N): The CVSS vector (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H) confirms the vulnerable routine is reachable over the network without prior authentication and without any user interaction. An attacker only needs network reachability to the web service port.
• Availability-only impact (C:N/I:N/A:H): The vulnerability does not yield a demonstrated confidentiality or integrity impact. The described consequence is denial of service — most plausibly a crash or hang of the web service or controller process when the oversized/malformed upload input corrupts stack memory, causing an abnormal termination.

The affected product families are Siemens building automation controllers: APOGEE MBC (PPC), APOGEE MEC (PPC), APOGEE PXC Compact and Modular (BACnet and P2 Ethernet variants), and TALON TC Compact and Modular (BACnet). These devices are typically deployed on building management system (BMS) networks and are frequently internet-exposed or reachable from corporate VLANs via building network segmentation gaps.

Insufficient technical detail is available in the provided description to identify the specific function, file path, API endpoint, or parameter name involved in the upload routine. No public proof-of-concept, exploit code, or Nuclei template has been published, and no EPSS score has been assigned by FIRST.org. The precise offset, buffer size, and trigger conditions are therefore not derivable from available data.

Exploitation Scenarios

The following chain is described at the vulnerability-class level; no specific endpoints or parameter names are invented because none are provided in the source data.

1. Reconnaissance / target identification. An attacker scans for the exposed web service of APOGEE/TALON controllers using the management interface HTTP/HTTPS ports. Shodan queries for BACnet (UDP 47808) and APOGEE/TALON web titles or page content can surface candidate devices on the public internet; internal reconnaissance targets building-automation subnets.

2. Triggering the flaw. The attacker identifies the input-validation weakness in the upload routine of the web service. Because validation is absent, a crafted upload request containing input exceeding the expected length is submitted. The description does not disclose the field or format, so the exact payload construction is unknown; the attack vector is an oversized/malformed upload submission to the unauthenticated web service.

3. Execution method. Per the vulnerable class (CWE-121), the malformed input overruns a stack buffer during processing. The reported outcome is denial of service rather than demonstrated code execution — the corrupted stack state leads to a service or controller fault.

4. Post-exploitation impact. A successful attack renders the targeted controller's web service (and potentially dependent control functions) unavailable. Given the affected product line, this can interrupt building automation monitoring and control until the device is recovered or restarted. No lateral movement or data exfiltration is described.

No public PoC is available; the attack chain is inferred strictly from the vulnerability class and CVSS characteristics.

Impact Assessment

• CVSS base score: 7.5 (HIGH). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.
• Attack Vector (Network): exploitable remotely over the network; the web service must be reachable.
• Attack Complexity (Low): no special conditions or race required per the vector.
• Privileges Required (None): no authentication needed — a critical property for exposed controllers.
• User Interaction (None): no victim action required.
• Scope (Unchanged): impact confined to the vulnerable component.
• Confidentiality (None) / Integrity (None): no demonstrated data disclosure or modification.
• Availability (High): the sole, but severe, impact — a total loss of availability of the affected service.

Blast radius. All versions of APOGEE MBC/MEC (PPC) and pre-fix APOGEE PXC and TALON TC controllers are affected. These devices underpin HVAC, energy management, and related building functions. Disruption of a controller can degrade environmental control, monitoring, and facilities operations, and may cascade to building occupants. Business impact centers on operational disruption and potential safety/compliance considerations in facilities where environmental or access systems are automated. CISA KEV status is NO, and no exploit-in-the-wild evidence is available at this time.

Detection Guidance

Sigma Rule

title: Potential CVE-2026-102076 APOGEE/TALON Web Upload Denial of Service
id: 9f3c1d20-7a4e-4c8b-9e21-2b6d5f10a8c4
status: experimental
description: Detects anomalous HTTP upload requests to APOGEE/TALON web service that may indicate exploitation of the unauthenticated stack buffer overflow (CWE-121).
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-102076
author: valtersit.com
logsource:
  category: webserver
detection:
  selection_method:
    cs-method: 'POST'
  selection_uri:
    cs-uri-stem|contains:
      - '/upload'
      - '/cgi-bin'
      - '/code'
  selection_size:
    sc-bytes|gt: 4096
  condition: selection_method and selection_uri and selection_size
falsepositives:
  - Legitimate firmware or configuration uploads performed by administrators
level: medium
tags:
  - attack.t1190

YARA Rule

rule CVE_2026_102076_APOGEE_Upload_Anomaly
{
    meta:
        description = "Detects oversized/malformed upload payloads targeting APOGEE/TALON web service implicated in CVE-2026-102076"
        author = "valtersit.com"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-102076"
        date = "2026-01-01"
        severity = "high"

    strings:
        $m1 = "POST" nocase
        $u1 = "upload" nocase
        $u2 = "Content-Disposition: form-data" nocase
        $p1 = "APOGEE" nocase
        $p2 = "TALON" nocase
        $p3 = "BACnet" nocase

    condition:
        uint16(0) == 0x504F and
        $m1 and $u1 and
        any of ($u2, $p1, $p2, $p3) and
        filesize > 8192
}

Suricata IDS Rule

alert http any any -> any any (msg:"CVE-2026-102076 APOGEE/TALON Web Upload Buffer Overflow Attempt"; flow:established,to_server; http.method; content:"POST"; http.uri; content:"upload"; nocase; dsize:>4096; threshold:type limit, track by_src, count 5, seconds 60; classtype:attempted-dos; reference:cve,2026-102076; sid:2026102076; rev:1;)

Elastic Detection

sequence by source.ip with maxspan=1m
  [ network where network.protocol == "http" and http.request.method == "POST" and
    stringContains(http.request.body.content, "upload") and http.request.body.bytes > 4096 ]

Splunk SPL Query

index=web OR index=proxy (http_method=POST)
| where match(lower(uri), "(?i)upload|(?i)cgi-bin|(?i)code")
| where bytes > 4096 OR content_length > 4096
| stats count min(_time) as first_seen max(_time) as last_seen by src_ip, uri, status
| where count >= 1
| convert ctime(first_seen) ctime(last_seen)
| sort - count

Wazuh OSSEC Rule

<group name="apogee,web,cve-2026-102076,">
  <rule id="102076" level="10">
    <decoded_as>web-accesslog</decoded_as>
    <match>POST</match>
    <regex>upload|cgi-bin|code</regex>
    <description>CVE-2026-102076: Possible APOGEE/TALON web service upload DoS attempt</description>
    <mitre>
      <id>T1190</id>
    </mitre>
    <group>attack,attempted_dos,</group>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 0/4 (UNPATCHED — no patch evidence from any tracked source).

1) Immediate mitigations.

• Isolate affected controllers from untrusted networks: firewall the web service ports so only authorized management hosts can reach them. Do not expose the web interface to the internet.
• Segment BMS/building-automation networks from corporate and OT/IoT networks; enforce least-privilege network paths (deny inbound from general VLANs and WAN).
• Restrict and monitor access to the upload routine; alert on unauthenticated or unexpected upload POST requests (see Detection Guidance).
• Where possible, disable the web management interface or upload functionality if not operationally required.

2) Patch / upgrade steps.

• APOGEE PXC Compact (BACnet): upgrade to V3.5.7 or later.
• APOGEE PXC Compact (P2 Ethernet): upgrade to V2.8.21 or later.
• APOGEE PXC Modular (BACnet): upgrade to V3.5.7 or later.
• APOGEE PXC Modular (P2 Ethernet): upgrade to V2.8.21 or later.
• TALON TC Compact (BACnet): upgrade to V3.5.7 or later.
• TALON TC Modular (BACnet): upgrade to V3.5.7 or later.
• APOGEE MBC (PPC) and MEC (PPC) — BACnet and P2 Ethernet: all versions are affected and no fixed version is identified; apply compensating network controls and consult Siemens for remediation status.
• Always validate upgrades against a representative test controller before fleet-wide rollout.

3) Long-term hardening.

• Maintain an inventory of all APOGEE/TALON controllers and continuously monitor firmware versions against vendor advisories.
• Enforce network segmentation and zero-trust access to building automation systems.
• Deploy IDS/IPS coverage on BMS segments and centralize logs from controllers and perimeter devices.
• Establish a vulnerability management cadence for OT/BMS assets, including patch tracking and compensating controls where no fix exists.

References

• NVD — CVE-2026-102076: https://nvd.nist.gov/vuln/detail/CVE-2026-102076
• CWE-121 — Stack-based Buffer Overflow: https://cwe.mit.edu/data/definitions/121.html
• Siemens ProductCERT / Security Advisories: https://www.siemens.com/cert/advisories (relevant APOGEE/TALON advisory)
• CISA Known Exploited Vulnerabilities Catalog: https://www.cisa.gov/known-exploited-vulnerabilities-catalog (CVE-2026-102076 not listed; KEV status NO)
• FIRST EPSS: https://www.first.org/epss (no score assigned)

No public proof-of-concept, exploit code, or in-the-wild exploitation campaign is known for CVE-2026-102076 at the time of writing.