CVE-2026-79551

Executive Summary

CVE-2026-79551 identifies a hardcoded cryptographic key embedded in the Tenda NVR_4H CH3 v2.1 network video recorder firmware, specifically build V27.5.58.6. Because the key is static across all units of this firmware, any attacker who extracts it — from a single device, a firmware image, or a public reverse-engineering write-up — can decrypt protected data, forge authenticated messages, or impersonate legitimate devices against every vulnerable unit in an organization's fleet. The vulnerability has no published CVSS score, no public proof-of-concept, no Nuclei template, and no vendor fix; EPSS is 0.00259 (17.8th percentile), indicating low but non-zero predicted exploitation activity driven by the large installed base of commodity NVRs and the triviality of abuse once the constant is known.

Technical Analysis

The NVD description states that "Tenda Technology Co., Ltd NVR_4H CH3 v2.1 V27.5.58.6 was discovered to contain a hardcoded cryptographic key." This is the entirety of the authoritative technical detail available; no CNA title, no CVSS vector, no CWE mapping, and no affected-version range beyond the single firmware build were supplied. Accordingly, this section analyzes the vulnerability class (CWE-321) rather than asserting implementation specifics that are not documented.

A hardcoded cryptographic key is a secret baked into compiled firmware at build time — a symmetric key (AES, DES), an HMAC signing key, a preshared secret, or a private key derivable from a fixed passphrase. The core defect is that the same secret exists in every deployed instance of the firmware. From an attacker's perspective, the cost of obtaining the key is paid once (extract from a purchased device, pull a firmware blob from a vendor download portal, or scrape a public blog post) and then amortized across the entire global population of that build. There is no per-device uniqueness and therefore no cryptographic separation between tenants, sites, or customers.

The attack surface depends on where the key is consumed. Common consumers in NVR/DVR firmware of this class include:

• Firmware update signing or encryption — if the update channel is signed or encrypted with a fixed key, an attacker who knows it can craft images the device will accept.
• Configuration or credential storage — encrypted config blobs or saved credentials that can be decrypted with the static key.
• Inter-device or client-to-device protocols — proprietary camera-to-NVR streams, mobile app pairing, or cloud heartbeat channels where a fixed key authenticates endpoints.
• Session tokens or license validation — predictable tokens enabling session forgery or license bypass.

Without a vendor advisory, the exact consumer cannot be confirmed. What can be stated with confidence is the cryptographic failure mode: secrecy of the key cannot be maintained, so any confidentiality or integrity guarantee that depends solely on it is void. This is the same structural weakness seen in CWE-321 findings across embedded/IoT products, where the practical exploitation step is often "extract strings from the firmware image" followed by "replay the key against the device or its companion service."

The device class matters for exposure. Network video recorders are typically internet-reachable via port-forwarded web UIs (TCP 80/443), RTSP (TCP 554), and vendor-specific management or P2P ports. They frequently sit flat on the LAN with camera VLANs and administrative workstations, giving a foothold value disproportionate to the device's perceived importance.

Exploitation Scenarios

No public proof-of-concept, exploit code, or Nuclei template exists for CVE-2026-79551. The attack chain below is therefore inferred from the vulnerability class (CWE-321) and the affected product category. It deliberately avoids naming functions, endpoints, or files that do not appear in the source data.

1) Reconnaissance / target identification. An adversary enumerates internet-exposed NVRs using Shodan/Censys queries matching Tenda NVR web interfaces ("Tenda", "NVR_4H", device favicon hashes) or scans internal ranges for RTSP/HTTP banners advertising the NVR_4H platform. Target confirmation requires identifying firmware build V27.5.58.6, typically exposed on the device's login or status page. Internal attackers — an on-network workstation, a compromised camera, or a visiting contractor on the CCTV VLAN — skip the internet-facing discovery step entirely.

2) Triggering the flaw class. Unlike a memory-corruption bug, CWE-321 requires no malformed input to trigger. The attacker instead obtains the hardcoded key by one of three routes: (a) extracting it from a firmware image acquired legitimately (vendor download / flash dump) and running offline analysis; (b) pulling it from a device they already control or have physical access to; or (c) reusing the key from a public disclosure or prior incident against a different unit of the same build. Because the key is identical on every V27.5.58.6 device, route (c) means one published extraction effectively arms every attacker against the entire population.

3) Payload / execution at the vulnerability-class level. With the key in hand, the attacker exercises whatever protected function consumes it. At the class level this means: decrypting captured or stored ciphertext that was protected with the key (configuration files, credential stores, captured protocol traffic); forging or tampering with messages that the key authenticates (making a modified payload verify as legitimate); or impersonating an authorized entity in a protocol that authenticates purely via the shared secret (a rogue camera, client, or management node). If the same key secures firmware or configuration updates, the attacker may be able to supply a crafted update the device accepts as genuine.

4) Post-exploitation impact. Successful key abuse yields the attacker the confidentiality and/or integrity of the protected channel. Realistic outcomes include recovery of stored credentials (which frequently grant administrative web-UI access), decryption of video streams or stored footage, hijacking of the management plane, and where update signing is affected, persistent code execution on the device. From the NVR, lateral movement toward camera networks and adjacent administrative hosts follows standard embedded-device tradecraft.

No evidence of in-the-wild exploitation, threat-actor campaigns, or KEV listing is associated with this CVE at the time of writing.

Impact Assessment

NVD publishes no CVSS score or vector for CVE-2026-79551, and no authoritative vector is available. The vector shown in METADATA (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N) is an analyst-inferred placeholder, not a vendor or NVD rating, and should not be cited as official. The rationale: exploitation is network-reachable for exposed devices (AV:N), requires no special conditions once the key is obtained (AC:L), permits pre-authentication abuse if the affected consumer is reachable unauthenticated (PR:N), and primarily breaks confidentiality (C:H) and integrity (I:H) of key-protected data, with availability (A:N) generally unaffected by key compromise itself.

Business impact concentrates in three areas. Confidentiality: decryption of surveillance footage, stored credentials, or management traffic — a serious privacy, legal, and physical-security exposure for any organization operating CCTV. Integrity and access control: forged authenticated messages or decrypted credentials can yield administrative control of the NVR, with knock-on access to camera VLANs and the recording archive. Fleet blast radius: because the key is a per-build constant, a single extraction compromises every V27.5.58.6 unit an organization owns — there is no partial exposure, and there is no way to rotate the secret within the affected build.

Sectors most exposed are those with large, distributed, internet-reachable NVR fleets: retail chains, multi-site logistics, healthcare and education campuses, municipal and small-business surveillance installs. The EPSS score (0.00259, 17.8th percentile) indicates the model currently assigns modest near-term exploitation probability; this is consistent with a vulnerability that is trivially exploitable once the key leaks but requires a one-time extraction or disclosure step that appears not to have happened publicly yet. EPSS should be re-read as a trend, not a floor.

Detection Guidance

Detection for a CWE-321 flaw focuses on the behavioral consequences of key abuse — anomalous administrative access, config/protocol manipulation, and firmware-integrity deviations — rather than on a specific exploit signature, none of which is published.

Sigma Rule

title: Suspicious Tenda NVR Administrative Access from Untrusted Source
id: 7c1e9a24-4b6f-4d2e-9f31-2a8b5c6d7e80
status: experimental
description: Detects anomalous administrative or management access to Tenda NVR_4H devices that may indicate post key-compromise abuse (CVE-2026-79551).
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-79551
author: valtersit.com
date: 2026/01/01
tags:
  - attack.t1552.001
  - attack.t1190
logsource:
  category: network_connection
  product: zeek
detection:
  selection_device:
    id.resp_h:
      - '10.0.0.0/8'
    id.resp_p:
      - 80
      - 443
      - 554
      - 8000
  selection_paths:
    http.uri|contains:
      - '/login'
      - '/cgi-bin/'
      - '/config'
  filter_known_admins:
    src_ip:
      - '10.0.10.0/24'
  condition: selection_device and selection_paths and not filter_known_admins
falsepositives:
  - Legitimate remote administrators outside the documented admin subnet
  - Vulnerability scanners
level: medium

YARA Rule

rule CVE_2026_79551_Tenda_NVR_Hardcoded_Key
{
    meta:
        description = "Hunts for indicators of hardcoded cryptographic key material in Tenda NVR_4H CH3 v2.1 firmware images / artifacts"
        author = "valtersit.com"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-79551"
        date = "2026-01-01"
        severity = "high"

    strings:
        $fw1 = "NVR_4H" ascii wide nocase
        $fw2 = "V27.5.58.6" ascii wide
        $fw3 = "CH3" ascii wide
        $kc1 = "hardcoded" ascii nocase
        $kc2 = "AES_KEY" ascii wide nocase
        $kc3 = "SECRET_KEY" ascii wide nocase
        $kc4 = "PRIVATE_KEY" ascii wide nocase
        $kc5 = "symmetric_key" ascii wide nocase

    condition:
        uint32(0) != 0x0164 and
        (
            (2 of ($fw1, $fw2, $fw3)) and
            any of ($kc*)
        )
}

Note: the key-material strings are generic crypto-symbol names, not values observed in this firmware; treat any hit as a triage lead only.

Suricata IDS Rule

alert http any any -> $HOME_NET any (msg:"CVE-2026-79551 Tenda NVR_4H Possible Key-Abuse Administrative Access"; flow:established,to_server; http.method; content:"GET"; http.uri; content:"/login"; http.header; content:"User-Agent|3a|"; reference:cve,2026-79551; classtype:attempted-admin; sid:90079551; rev:1; metadata:created_at 2026_01_01, updated_at 2026_01_01;)

Elastic Detection (EQL)

network where event.category == "network" and
  network.direction == "inbound" and
  destination.port in (80, 443, 554, 8000) and
  process.name != null and
  not source.ip in ("10.0.10.0/24") and
  destination.ip in ("10.0.0.0/8")

Splunk SPL Query

index=network sourcetype=stream:http
| search (dest_port=80 OR dest_port=443 OR dest_port=554 OR dest_port=8000)
| where match(uri, "(?i)/(login|config|cgi-bin)")
| lookup nvr_assets dest_ip OUTPUT device_type, firmware_build
| where firmware_build="V27.5.58.6" AND NOT cidrmatch("10.0.10.0/24", src)
| stats count values(uri) as uris by src, dest_ip, firmware_build
| where count > 10
| sort - count
| table src, dest_ip, firmware_build, count, uris

Wazuh OSSEC Rule

<group name="tenda_nvr,cve_2026_79551,">
  <rule id="100551" level="8">
    <if_sid>31100</if_sid>
    <id>^/login|^/config|^/cgi-bin</id>
    <description>CVE-2026-79551: Possible key-abuse access to Tenda NVR_4H management interface</description>
    <mitre>
      <id>T1552.001</id>
      <id>T1190</id>
    </mitre>
  </rule>
  <rule id="100552" level="12">
    <if_sid>100551</if_sid>
    <field name="srcip">!10.0.10.0/24</field>
    <description>CVE-2026-79551: NVR management access from unexpected source; escalate</description>
    <group>authentication_failed,pci_dss_10.2.4,</group>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 0/4 — UNPATCHED. No patch evidence from any tracked source. There is no vendor fix, no workaround, and no affected-version range published by the vendor. The rules below are compensating controls, not remediation.

1) Immediate mitigations.

• Remove internet exposure. Enumerate all NVR_4H devices and close inbound port-forwarding for the web UI, RTSP, and any vendor P2P/cloud service. Force remote viewing through a VPN or an authenticated zero-trust gateway. This single control removes the remote attack path for the dominant exploitation scenario.
• Segment the surveillance plane. Place NVRs and cameras on a dedicated VLAN with deny-by-default rules to user and server segments; allow only an explicit management jump host. This limits both initial access from a compromised workstation and post-exploitation lateral movement.
• Rotate any secrets that transit the device. Assume credentials stored or transmitted with the key may be recoverable. Rotate NVR admin passwords, camera credentials, and any shared secrets the NVR touches; enforce unique per-device credentials.
• Block egress and update channels if update-signing is in scope. Until the consumer of the key is confirmed, treat device-initiated update/cloud traffic as untrusted and restrict it.

2) Patch / upgrade steps.

• Monitor the Tenda security advisory channel and NVD for a fixed build; no patched version exists at this time.
• Where hardware replacement is possible, migrate affected units to a supported model line with a documented secure-firmware/update program.
• If Tenda publishes a fixed firmware, upgrade offline (local flash of a vendor-verified image), verify the hash in a lab unit, and re-baseline each device after upgrade.

3) Long-term hardening.

• Maintain an accurate firmware/CVE inventory for all embedded devices; you cannot mitigate a per-build constant key you cannot enumerate.
• Require verifiable per-device key provisioning and rotation in procurement criteria for NVR/camera products.
• Enforce certificate-based or per-device authentication over shared-secret designs for all management and inter-device protocols.
• Deploy the Sigma/Suricata/Wazuh detections above to catch post-compromise administrative access from unexpected sources.

References

1. NVD — CVE-2026-79551: https://nvd.nist.gov/vuln/detail/CVE-2026-79551
2. CWE-321 — Use of Hard-coded Cryptographic Key: https://cwe.mitre.org/data/definitions/321.html
3. FIRST EPSS — CVE-2026-79551 score (0.00259): https://api.first.org/data/v1/epss?cve=CVE-2026-79551
4. Tenda security advisory channel (monitor for a fixed NVR_4H build): https://www.tenda.com.cn/ (official security notices — no advisory currently published for this CVE)
5. CISA Known Exploited Vulnerabilities catalog (checked; CVE-2026-79551 is not listed as of this report): https://www.cisa.gov/known-exploited-vulnerabilities-catalog

Threat-actor / exploit-in-the-wild status: No public PoC, no exploit code, no Nuclei template, no KEV listing, and no attributed threat-actor campaign identified at the time of writing. EPSS 0.00259 reflects low predicted near-term exploitation. The low score should be re-evaluated if the hardcoded key is publicly disclosed or if extraction tooling for this firmware appears — at that point, exploitation against the entire V27.5.58.6 population becomes trivial and the risk profile changes abruptly.