CVE-2026-90607

Executive Summary

CVE-2026-90607 is a remote buffer overflow vulnerability in the Totolink A3002MU wireless router running firmware Hh-B20211125.1046, reachable through the formNewSchedule function exposed by the device's boa web server at /boafrm/formNewSchedule. An authenticated remote attacker can overflow a stack/heap buffer by manipulating the submit-url argument, leading to memory corruption and potential arbitrary code execution with the privileges of the boa daemon. With a CVSS v3.1 base score of 9.9 and public exploit availability, the vulnerability represents a critical risk to any A3002MU device exposed to untrusted networks.

Technical Analysis

The vulnerability resides in the Boa HTTP server component (boa) embedded in Totolink A3002MU firmware build Hh-B20211125.1046. Boa is a lightweight, single-threaded web server widely used in embedded consumer networking equipment. Totolink extends Boa with custom form* handler functions that parse user-supplied form fields for configuration operations. CVE-2026-90607 affects formNewSchedule, an endpoint responsible for creating scheduled tasks (for example, recurring wireless or reboot schedules) configured through the device's administrative interface.

The vulnerable code path is exposed at the URI /boafrm/formNewSchedule. According to the NVD description, the function formNewSchedule fails to validate the length of the submit-url form parameter before copying it into a fixed-size destination buffer. The manipulation of this argument results in a classic buffer overflow, mapped to CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). The description does not specify whether the overflow is stack-based or heap-based, nor does it disclose the exact buffer size, copy primitive (strcpy, sprintf, memcpy, etc.), or whether a length check is present but bypassable. Those specifics must be determined by reverse engineering the firmware image; they are not derivable from available public data.

Two contextual factors elevate severity. First, the network vector (AV:N) combined with low attack complexity (AC:L) means no race condition or unusual precondition is required beyond delivering a crafted HTTP request. Second, the scope change (S:C) indicates that a successful exploit can affect resources beyond the vulnerable component — a realistic outcome when overflowing memory in a web server that holds the device's administrative session state. The PR:L rating reflects that the endpoint requires some level of authorization (the description notes it is part of the administrative management interface). However, embedded router authentication is frequently weak, trivially bypassed via default credentials, session prediction, or adjacent vulnerabilities, meaning the practical barrier to exploitation for an attacker with network access is low.

The exploit is publicly available, increasing the likelihood of automated scanning and weaponization. Boa-based Totolink endpoints are routinely indexed by internet-wide scanners, and public proof-of-concept material tends to be rapidly absorbed into IoT botnet tooling.

Exploitation Scenarios

Precondition note: No public PoC artifact is included in the provided intelligence, and no Nuclei template or exploit code reference was supplied. The attack chain below is described at the vulnerability-class level and uses only identifiers explicitly named in the NVD description (formNewSchedule, /boafrm/formNewSchedule, boa, submit-url). No additional function names, parameters, or file paths are inferred.

1. Reconnaissance / target identification. The attacker identifies exposed Totolink A3002MU devices, for example through internet-wide scanning for the Boa management interface or for the /boafrm/formNewSchedule path. Devices reachable from the WAN or from a shared network segment are the primary targets.

2. Authentication and request construction. Because the vulnerable endpoint is part of the administrative surface, the attacker first establishes a session (valid credentials, reused default credentials, or an existing authenticated context). The attacker then constructs an HTTP request to /boafrm/formNewSchedule that includes the submit-url form parameter.

3. Triggering the overflow. The attacker supplies an oversized value for submit-url. Because formNewSchedule in the boa component does not bound the length of this argument before processing it, the value overflows the destination buffer in memory. The exact payload structure needed to convert the overflow into control-flow hijacking depends on the memory layout of this specific firmware build, which is not publicly documented in the supplied data.

4. Post-exploitation impact. Successful exploitation yields memory corruption within the boa process. Given CVSS impact ratings of High for confidentiality, integrity, and availability, a working exploit can plausibly achieve arbitrary code execution in the context of the web server, enabling device takeover, configuration tampering, credential theft, or use of the router as a pivot or botnet node. The scope-change rating reinforces that impact may extend beyond the web service itself.

Impact Assessment

CVE-2026-90607 carries a CVSS v3.1 base score of 9.9 (Critical) with the vector CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H. The subscores indicate:

• Attack Vector (Network): exploitable remotely over the network, not requiring physical or local access.
• Attack Complexity (Low): no specialized conditions or race windows needed.
• Privileges Required (Low): the attacker needs some authenticated context on the administrative interface; in practice, default or weak credentials on consumer routers reduce this barrier substantially.
• User Interaction (None): exploitation does not depend on a victim clicking a link or opening a file.
• Scope (Changed): impact crosses a trust boundary — compromise of the web component can affect the broader device.
• Confidentiality / Integrity / Availability (High): full loss of confidentiality, integrity, and availability is possible within the affected component.

Blast radius. Affected systems are Totolink A3002MU units running firmware Hh-B20211125.1046. Because consumer routers frequently sit at the network edge and are used in SOHO, retail, and remote-branch environments, a successful exploit can yield a persistent foothold at the perimeter, enabling traffic interception, DNS manipulation, lateral movement into internal networks, and enrolment in IoT botnets. The CVSS rating of 9.9 places this in the highest severity tier, and public exploit availability means the window between disclosure and active abuse is likely short. This CVE is not listed in CISA KEV, so there is no confirmed evidence of in-the-wild exploitation as of this report, but the public exploit disclosure makes opportunistic exploitation probable.

Detection Guidance

Sigma Rule

title: Suspicious Oversized submit-url Parameter to Totolink formNewSchedule
id: 8f3c1a72-4b9e-4d21-9c77-totolink90607
status: experimental
description: Detects HTTP requests to /boafrm/formNewSchedule containing an abnormally long submit-url parameter, indicative of CVE-2026-90607 buffer overflow attempts against Totolink A3002MU firmware.
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-90607
author: valtersit.com
date: 2026/01/01
logsource:
  category: webserver
detection:
  selection_uri:
    cs-uri-stem|contains: '/boafrm/formNewSchedule'
  selection_param:
    cs-uri-query|contains: 'submit-url='
  selection_length:
    cs-uri-query|re: '(?i)submit-url=.{256,}'
  condition: selection_uri and selection_param and selection_length
fields:
  - c-ip
  - cs-uri-stem
  - cs-uri-query
  - cs-user-agent
falsepositives:
  - Legitimate administrative configuration with unusually long URLs (rare).
level: high
tags:
  - attack.t1190
  - cve.2026.90607

YARA Rule

rule CVE_2026_90607_Totolink_A3002MU_formNewSchedule
{
    meta:
        description = "Detects exploit artifacts and firmware references related to CVE-2026-90607 (Totolink A3002MU boa formNewSchedule submit-url buffer overflow)"
        author = "valtersit.com"
        date = "2026-01-01"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-90607"
        severity = "critical"

    strings:
        $uri   = "/boafrm/formNewSchedule" ascii wide nocase
        $func  = "formNewSchedule" ascii wide nocase
        $param = "submit-url" ascii wide nocase

    condition:
        (uint16(0) == 0x5A4D or true) and
        any of ($uri, $func) and $param
}

Suricata IDS Rule

alert http any any -> any any (msg:"CVE-2026-90607 Totolink A3002MU formNewSchedule submit-url Buffer Overflow Attempt"; flow:established,to_server; http.uri; content:"/boafrm/formNewSchedule"; http.uri; content:"submit-url="; http.uri; pcre:"/submit-url=[^&\s]{256,}/i"; classtype:attempted-admin; reference:cve,2026-90607; reference:url,nvd.nist.gov/vuln/detail/CVE-2026-90607; sid:9060701; rev:1;)

Elastic Detection

// Detects long submit-url values sent to the vulnerable Totolink endpoint (CVE-2026-90607)
network where
  network.protocol == "http" and
  url.path == "/boafrm/formNewSchedule" and
  stringContains(url.query, "submit-url=") and
  length(url.query) > 300

Splunk SPL Query

index=web OR index=proxy sourcetype=access_combined OR sourcetype=stream:http
| where like(uri_path, "%/boafrm/formNewSchedule%")
| eval qlen = len(uri_query)
| where qlen > 300 AND match(uri_query, "(?i)submit-url=")
| stats count min(_time) as first_seen max(_time) as last_seen by src_ip, uri_path, uri_query
| sort - count

Wazuh OSSEC Rule

<group name="web,attack,cve-2026-90607,">
  <rule id="906071" level="12">
    <decoded_as>web-accesslog</decoded_as>
    <url>/boafrm/formNewSchedule</url>
    <regex type="pcre2">submit-url=[^&amp;\s]{256,}</regex>
    <description>CVE-2026-90607: Possible buffer overflow attempt against Totolink A3002MU formNewSchedule via oversized submit-url parameter.</description>
    <mitre>
      <id>T1190</id>
    </mitre>
    <group>web_scan,attack.t1190,</group>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 0/4 — UNPATCHED. No vendor fix, firmware update, or advisory was identified from any tracked source, and no affected-version range or OSV package mapping is available. The firmware version Hh-B20211125.1046 is the last known reference point and must be treated as vulnerable.

1) Immediate mitigations

• Remove all internet-facing exposure of the Totolink A3002MU administrative interface. Disable WAN-side remote management and UPnP port forwarding to the management port.
• Segment IoT/edge routers onto isolated VLANs so that a compromise cannot pivot into business-critical networks.
• Restrict access to the boa management interface (including /boafrm/formNewSchedule) to trusted administrative hosts only, via firewall ACLs.
• Replace default and weak administrative credentials with strong, unique passwords immediately — the CVSS PR:L rating is only a partial barrier given common consumer-router credential weaknesses.
• If the device is no longer supported or not essential, decommission or replace it with a maintained product.

2) Patch / upgrade steps

• No patch exists. Monitor Totolink's official support channels and the A3002MU firmware download page for a fixed build. Do not assume an update resolves this issue unless the vendor explicitly references CVE-2026-90607 or the formNewSchedule submit-url handling.
• Where no fixed firmware becomes available, treat the device as end-of-secure-life and plan hardware replacement.

3) Long-term hardening

• Maintain an inventory of edge and IoT devices with firmware version tracking, so unpatched or EOL units are surfaced automatically.
• Enforce network monitoring for anomalous Boa requests (see detection guidance above) and alert on oversized parameters targeting form* endpoints.
• Adopt a policy of not exposing consumer-grade router management planes to untrusted networks; favour VPN-only administrative access.
• Subscribe to NVD and vendor advisories for the Totolink product line so that a future fix is applied promptly.

References

1. NVD — CVE-2026-90607: https://nvd.nist.gov/vuln/detail/CVE-2026-90607
2. CWE-119 — Improper Restriction of Operations within the Bounds of a Memory Buffer: https://cwe.mitre.org/data/definitions/119.html
3. MITRE ATT&CK T1190 — Exploit Public-Facing Application: https://attack.mitre.org/techniques/T1190/
4. Totolink official product/support site (monitor for A3002MU firmware updates): https://www.totolink.net/
5. FIRST EPSS — CVE-2026-90607 (not yet scored at time of writing): https://api.first.org/data/v1/epss?cve=CVE-2026-90607

Exploitation status: Public exploit code is reported to exist per the NVD description. No threat-actor campaign attribution is available, and CVE-2026-90607 is not listed in CISA KEV as of this report. No confirmed in-the-wild exploitation evidence was provided in the source intelligence.