CVE-2026-50720

Executive Summary

CVE-2026-50720 is a cryptographic verification bypass vulnerability in the Ingenic T31 System-on-Chip (SoC) boot ROM flash-boot verification path. The flawed implementation compares only a single 32-bit word of the RSA signature output against a single 32-bit word of the SHA-256 payload digest instead of performing a full cryptographic comparison, enabling forgery of modified SPL (Secondary Program Loader) images without possession of the OEM signing key. Affected devices include the Wyze Video Doorbell v2 (T31X) and any other product built on the Ingenic T31 SoC. An attacker with physical access to boot media can achieve persistent arbitrary code execution at the bootloader level with approximately 2/3 success probability per attempt, effectively defeating secure boot and enabling firmware-level implant installation.

Technical Analysis

The vulnerability resides in the Ingenic T31 SoC's boot ROM (ROM code) responsible for verifying the integrity and authenticity of the SPL (Secondary Program Loader) during the flash-boot sequence. The boot ROM is mask-programmed silicon — it cannot be patched or updated via firmware. This makes the vulnerability inherently persistent across all software updates.

Vulnerability Mechanism: During the secure boot verification process, the boot ROM performs an RSA signature verification over the SPL image and compares the resulting digest against a stored SHA-256 hash of the expected payload. The critical flaw: rather than comparing the full RSA signature output (typically 256 bytes for RSA-2048) against the full SHA-256 digest (32 bytes), the implementation truncates both values and compares only a single 32-bit word (4 bytes). This is a classic "short-circuit comparison" bug where only a micro-fraction of the cryptographic output is actually checked.

Attack Surface:

• Physical access required: The attacker must be able to write to the boot media (e.g., SPI NOR flash chip on the device's PCB or removable SD/eMMC depending on board design).
• Boot ROM executes before any OS: The vulnerable code runs at the earliest stage of the boot process, before any software-level protections (kernel, TEE, etc.) are active.
• No authentication or anti-rollback bypass needed: The flaw is intrinsic to the verification comparison logic, not to key management or rollback protection.

Statistical Analysis: Each forgery attempt has approximately 2/3 (≈66.7%) probability of success. This arises because the SHA-256 digest of the modified payload is random-looking; when comparing only two 32-bit words, the probability of a match is 2^-32 ≈ 2.3e-10 per attempt. However, the reported 2/3 success rate indicates the comparison may be a partial match of word combinations (e.g., OR of several word comparisons) or that the verification path is trivially bypassable with error-correction loops. The exact mechanics are not fully disclosed in the NVD description.

Validation Evidence: The vulnerability is validated through: (1) reverse engineering of the boot ROM binary, (2) software emulation against legitimate vendor-signed images to confirm the comparison flaw, and (3) end-to-end hardware acceptance of a forged firmware image on a Wyze Video Doorbell v2 — proving practical exploitability.

Exploitation Scenarios

Prerequisites: Physical access to device; ability to desolder or program the SPI NOR flash (or access a boot media write port). No network-based exploitation is feasible.

Step 1 — Reconnaissance/Target Identification:

• Attacker identifies target device (e.g., Wyze Video Doorbell v2) and confirms it uses the Ingenic T31 SoC.
• Physical access is obtained: device removed from deployment, opened, or otherwise accessed at the circuit board level.
• Attacker dumps the original boot media contents (e.g., via SPI programmer) to analyze the SPL layout and the flash-boot descriptor structures.

Step 2 — Flaw Trigger:

• Attacker modifies the SPL binary to include malicious code (e.g., a backdoor, network implant, or firmware replacement).
• The attacker recalculates the SHA-256 digest for the modified payload and embeds a fake RSA signature (random 256-byte value).
• The attacker writes the forged image to the boot media. When the device powers on, the boot ROM reads the image, performs RSA verification (with the fake signature), extracts the SHA-256 digest, and compares only the first 32-bit word of the digest against the first 32-bit word of the RSA output.

Step 3 — Payload/Execution:

• If the 32-bit words coincide (≈2/3 probability per attempt), the forged SPL passes verification and executes.
• On failure, the device fails to boot; attacker retries with a new random signature block (statistical brute-force via power cycling).
• Successful execution grants the attacker arbitrary code execution at the earliest boot stage — before any OS, TEE, or secure element protections are active.

Step 4 — Post-Exploitation:

• The malicious SPL can: (a) persist a rootkit or backdoor in the final firmware image, (b) disable security features (encryption, attestation), (c) exfiltrate sensitive data stored in eMMC/flash, (d) enable remote access via network services.
• The device becomes fully attacker-controlled with no software-level detection possible at boot time (since the boot ROM accepts the forged image).
• Note: No public PoC is available; the attack chain is inferred from the vulnerability class and the NVD description of hardware-accepted forgery.

Impact Assessment

Business Impact (per device):

• Complete compromise of device integrity: attacker controls boot chain persistently.
• Data confidentiality breach: access to any secrets stored on the device (credentials, videos captured by the doorbell, Wi-Fi passwords).
• Availability loss: malicious images can brick devices or render them non-functional.
• Supply chain risk: if an OEM ships devices with T31 SoC, the entire product line's trust boundary is invalidated.

Affected Systems:

• All devices using Ingenic T31 (T31X) SoC. Known: Wyze Video Doorbell v2. Unknown but likely: other Wyze models, dashboard cameras, IP cameras, and IoT products using Ingenic T31.

Blast Radius:

• CVSS vector indicates a high impact (C: High, I: High, A: High) with a scope change (S: C) — compromise of the boot ROM verification effectively compromises the entire device security domain.
• Due to the 2/3 per-attempt success probability, exploitation is relatively cheap (typical 1–2 attempts) but requires physical access, limiting mass-scale remote exploitation.

CISA KEV: Not listed. EPSS: Not yet scored. CVSS: N/A (vendor scoring not published; the vector above is an analyst estimate based on the vulnerability class — note this in reporting).

Detection Guidance

Detection of this vulnerability is extremely challenging because exploitation occurs during the boot phase, before any operating system, security agent, or logging mechanism is active. The following detections focus on secondary indicators: device behavior anomalies, post-exploitation artifacts, and preparation phases.

Sigma Rule

title: Ingenic T31 Boot Media Forgery - Device Firmware Modification
id: 4f7a9c2d-8b4e-4b6a-9c1f-2d3e4f5a6b7c
status: experimental
description: Detects anomalous firmware reflash activity or device boot failures on Ingenic T31-based hardware
logsource:
  product: linux
  service: syslog
detection:
  selection_bootfail:
    - keywords: ["SPL", "secure boot", "verification failed", "boot rom"]
    - message|contains|all:
        - "flash-boot"
        - "RSA"
        - "compare"
  selection_uboot:
    - keywords: ["U-Boot", "SPL", "firmware upgrade"]
  condition: selection_bootfail or selection_uboot
level: critical
falsepositives:
  - Legitimate firmware upgrades (distinguish via vendor signature)
  - Hardware failures causing boot error messages
tags:
  - attack.t1211
  - cve.2026-50720

YARA Rule

rule Ingenic_T31_Forged_SPL
{
    meta:
        author = "Valterit SOC"
        description = "Detects SPL images with mismatched RSA/SHA signatures or anomalous secure-boot descriptors for Ingenic T31 SoC"
        cve = "CVE-2026-50720"
        date = "2026-06-01"
    strings:
        $t31_sig = { 54 33 31 (00 | 58) }  // "T31" or "T31X" marker in header
        $spl_magic = { 53 50 4C 00 }        // "SPL" magic bytes
        $sha_short = { 00 00 00 00 00 00 00 00 } // truncated digest region
        $rsa_weak = { 00 00 00 00 FF FF FF FF }  // typical fake RSA signature pads
    condition:
        uint16(0) == 0x3354 and  // "T3" in header
        any of ($t31_sig*) and
        any of ($spl_magic) and
        (any of ($sha_short) or any of ($rsa_weak))
}

Suricata IDS Rule

alert tcp any any -> any any (msg:"CVE-2026-50720 Ingenic T31 Boot Media Exfiltration Attempt"; flow:established; content:"SPL"; depth:16; content:"firmware"; within:64; content:"update"; within:128; classtype:attempted-admin; sid:2026072001; rev:1; metadata:cve CVE-2026-50720;)

Note: Network-based detection is of limited utility since exploitation requires physical access; this rule is intended to catch post-exploitation firmware exfiltration or malicious update traffic from compromised devices.

Elastic Detection

sequence by host.id with maxspan=1h
  [ any where event.code : "firmware_write" and process.name : "*uboot*" ]
  [ any where process.name : "*fw_upgrade*" or event.action : "boot_failure" ]

Alternative EQL for device logs:

any where process.name : "fwflash" and winlog.event_data.CommandLine : "*--force*" and not user.name : "vendor_admin"

Splunk SPL Query

index=ntsoc OR index=iot index=main
| search "secure boot" OR "SPL" OR "verification failed"
| eval risk_score = case(
    match(_raw, "T31|T31X|boot rom|flash-boot"), 80,
    match(_raw, "firmware upgrade|uboot"), 40,
    true(), 5)
| where risk_score > 20
| stats count by host, source, _time, risk_score
| sort - risk_score

Wazuh OSSEC Rule

<group name="inetgenic_cve_2026_50720,">
  <rule id="100702" level="15">
    <decoded_as>syslog</decoded_as>
    <match>secure boot|SPL|verification failed|boot rom|flash-boot</match>
    <description>CVE-2026-50720 Ingenic T31 boot verification anomaly (possible forgery attempt)</description>
    <group>cve,iot,hardware,</group>
  </rule>
  <rule id="100703" level="12">
    <decoded_as>syslog</decoded_as>
    <match>firmware|uboot|reflash|upgrade</match>
    <description>Firmware modification activity on Ingenic T31 device</description>
    <group>cve,iot,hardware,</group>
  </rule>
</group>

Mitigation & Patch Guidance

Patch Confidence: 0/4 — UNPATCHED. The Ingenic T31 boot ROM is mask-ROM silicon and cannot be updated. No vendor patch exists or is expected. All affected devices remain vulnerable indefinitely.

Immediate Mitigations (compensating controls):

1. Physical security: Restrict physical access to devices. Deploy tamper-evident enclosures, epoxy-sealed boards, or monitored enclosures to deter boot-media access.
2. Boot-media write protection: Where hardware permits, set SPI flash write-protect pins (WP#) to prevent in-circuit reprogramming.
3. Post-boot attestation: Deploy an integrity monitoring agent (e.g., TPM-based remote attestation) that runs immediately after SPL execution to detect if the boot chain was tampered, even if the boot ROM was bypassed.

Patch/Upgrade Steps:

• No software update can fix this flaw. Hardware revision (e.g., a newer SoC with corrected boot ROM) is the only permanent fix. OEMs should:
  • Transition to newer Ingenic SoC revisions (T31B/C or T40) with validated full-size signature comparison.
  • Or switch to a different SoC vendor with audited secure boot.
• For Wyze devices: contact vendor for hardware replacement program; no firmware update will address CVE-2026-50720.

Long-Term Hardening:

1. Procurement policy: Vendors must require proof of secure boot verification completeness (full digest comparison) in SoC selection.
2. Boot ROM audit: For existing fleet, conduct physical security risk assessments; assume devices deployed in untrusted locations are compromised.
3. Segmentation: Isolate IoT devices on separate network segments to limit blast radius if compromised.
4. Monitoring: Deploy the detection rules above (Syslog/EDR on device or adjacent gateway) to catch post-exploitation artifacts.
5. Rotation: If device compromise is detected, treat all device secrets (Wi-Fi passwords, cloud tokens) as compromised and rotate them.

References

1. NVD Entry: https://nvd.nist.gov/vuln/detail/CVE-2026-50720
2. Researcher Validation: (no public researcher blog available; validation is cited in NVD as reverse engineering + emulation + hardware acceptance)
3. Wyze Security Advisory: https://support.wyze.com/security-advisories (check for current advisory; no fix announced)
4. Ingenic Semiconductor Product Page: https://www.ingenic.com.cn/en/product/ (T31 series datasheets)
5. CISA KEV: https://www.cisa.gov/known-exploited-vulnerabilities-catalog (CVE-2026-50720 NOT listed)

Threat Actor Activity: No evidence of exploit-in-the-wild or known threat actor campaigns targeting this CVE as of reporting date. Exploitation requires physical access and is therefore likely used in targeted operations (law enforcement, espionage, or organized theft of device data) rather than mass exploitation. The 2/3 success probability makes the attack practical for a technician with a soldering iron and SPI programmer, but the physical-access requirement limits its appeal for cybercriminal botnets.