CVE-2026-73376

Executive Summary

CVE-2026-73376 is a critical, unauthenticated PHP Object Injection (CWE-502) vulnerability affecting Supsystic Ultimate Maps versions prior to 1.5.0. An unauthenticated remote attacker can submit crafted serialized PHP object data to the affected component, potentially achieving arbitrary code execution, data exfiltration, and full compromise of the underlying web application. With a CVSS base score of 9.8 and no evidence of an available vendor patch, any internet-exposed instance running the affected versions should be treated as critically at-risk.

Technical Analysis

The NVD description is limited to: "Unauthenticated PHP Object Injection in Ultimate Maps by Supsystic < 1.5.0 versions." No specific entry point, parameter name, HTTP endpoint, or affected function is disclosed in the CNA title or NVD description. The following analysis is therefore presented at the vulnerability-class level (CWE-502) and is not an assertion of the vendor's internal implementation.

Vulnerability class — unsafe deserialization. PHP Object Injection occurs when untrusted user input is passed to a PHP deserialization routine without adequate validation or sanitization. In the PHP ecosystem, the canonical sink is unserialize(); when an attacker controls the serialized string supplied to this sink, they can instantiate arbitrary PHP objects with attacker-controlled property values. The PHP serialization format encodes objects using tokens of the form O:<class_name_length>:"<ClassName>":<property_count>:{...}. Because the length-prefixed format makes the payload parser-driven, an attacker can precisely control the class and property values of the crafted object graph.

Gadget (POP) chain exploitation. Instantiation alone is not enough to achieve code execution — the attacker must leverage "magic methods" invoked automatically by the PHP engine during object lifecycle events, such as __wakeup(), __destruct(), __toString(), or __call(). These methods exist throughout the application and its dependencies. By chaining objects whose magic methods perform sensitive operations — writing files, issuing SQL queries, including files, or making networked calls — an attacker can escalate from object injection to arbitrary code execution or data exfiltration. This is commonly referred to as a Property-Oriented Programming (POP) chain. The success of exploitation depends on the presence of suitable gadgets within the plugin and the PHP runtime environment, but it is a well-established and largely reliable technique against PHP applications.

Attack surface. The affected component, Ultimate Maps by Supsystic, is a PHP-based web application plugin (naming and versioning conventions are consistent with Supsystic's WordPress plugin ecosystem, though the NVD description does not explicitly name the hosting platform). Map configuration, marker import, and settings-management functionality typically accept serialized or structured data, making any such unauthenticated handler a candidate entry point. The vulnerability is described as unauthenticated, meaning no session, authentication token, or privileged role is required to reach the vulnerable sink.

Severity context. The CVSS vector — AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H — reflects a network-reachable, low-complexity, fully unauthenticated flaw with maximum confidentiality, integrity, and availability impact. The "Scope: Unchanged" component indicates the compromise is confined to the affected application context, but the combination of high C/I/A ratings makes this a de-facto remote code execution primitive in practice.

Known limitations of available data. No patch advisory from Supsystic, no commit reference, no CISA KEV entry, no EPSS score, and no public PoC or exploit code have been identified at the time of writing. Detection and mitigation below are therefore class-level and should be validated against the actual vendor release when it becomes available.

Exploitation Scenarios

No public PoC is available; the attack chain described below is inferred from the vulnerability class (CWE-502, PHP Object Injection) and the CVSS attributes.

Step 1 — Reconnaissance / target identification. An attacker fingerprints candidate targets by identifying web applications running Ultimate Maps by Supsystic. This can be done by requesting known static assets traditionally shipped with the plugin (e.g., JavaScript/CSS files referencing the product name), scanning for the vendor string "supsystic" in HTML source and headers, or using search engines and Shodan dorks. Version identification is then performed by comparing asset hashes, version query parameters, or generator meta tags against known releases, allowing the attacker to confirm whether the target is in the affected range (< 1.5.0). Because the vulnerability is unauthenticated, no prior account creation or privilege acquisition is required.

Step 2 — Triggering the flawed deserialization pathway. The attacker crafts a malicious HTTP request — most plausibly a POST request to an unauthenticated endpoint that processes plugin configuration, map data, or import/export functionality. The request body or query parameter carries a PHP serialized payload where an O: object token is substituted for a legitimate scalar or array value the application expects. Since the flaw is unauthenticated, this request is sent directly against the public-facing interface with no session cookie or authentication header. The exact endpoint and affected parameter are not disclosed in the NVD description, so the attacker would locate them through source-code review of the plugin or differential testing between versions < 1.5.0 and 1.5.0.

Step 3 — Payload execution via object injection. The serialized payload is passed to the application's deserialization logic. PHP reconstructs the attacker-specified objects, and, upon object destruction or other lifecycle events, invokes magic methods. Using a POP chain composed of gadget classes present in the plugin core or its bundled libraries, the attacker converts object construction into a side effect such as writing a PHP web shell to the web root, reading arbitrary files (/etc/passwd, wp-config.php if a WordPress deployment), or executing operating-system commands through a gadget that invokes a process-execution primitive. The payload can be delivered raw or obfuscated with base64 encoding to evade naive signature-based inspection.

Step 4 — Post-exploitation and persistence. With code execution achieved under the web server user, the attacker deploys a web shell or backdoor, establishes persistence across restarts, and escalates privileges subject to the hosting environment's OS-level hardening. Impacted data includes the application's database credentials, map API keys, and any customer data rendered through the maps component. The unauthenticated, network-only nature of the exploit means this can be executed in a fully automated manner at scale, consistent with mass web-shell campaigns routinely observed against PHP plugin vulnerabilities in the wild.

Impact Assessment

The vulnerability is rated Critical with a CVSS v3.1 base score of 9.8 (Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H).

• Confidentiality (High): An attacker can read arbitrary files accessible to the web server user, including application configuration files, database credentials, and API keys used by the mapping service. Theft of these secrets enables downstream compromise of adjacent systems.
• Integrity (High): Arbitrary code execution permits writes to the web root, injected backdoors, site defacement, and manipulation of map configuration and served content. Compromised sites can be weaponized for search-engine optimization (SEO) spam or credential phishing.
• Availability (High): An attacker can delete application files, corrupt the database, or exhaust server resources, resulting in denial of service.

Affected systems / blast radius. All deployments of Ultimate Maps by Supsystic with versions below 1.5.0 are potentially exploitable from the network without authentication. The blast radius is widened by the plugin's deployment model: web hosting environments typically run multiple applications and databases under shared web-server user accounts, so a single exploited instance can expose co-hosted application data and may facilitate lateral movement to adjacent virtual hosts. The lack of a confirmed vendor patch (patch confidence 0/4) means vulnerable installations cannot currently be remediated by an official upgrade path; they remain exposed until Supsystic publishes a fixed release or until operators apply compensating controls.

Threat landscape context. EPSS has not yet scored this CVE, and CISA has not added it to the Known Exploited Vulnerabilities catalog. There is no evidence of active exploitation campaigns and no public PoC at the time of writing. However, the unauthenticated, high-severity profile of this flaw class is historically attractive to opportunistic botnets; enterprises should expect scanning activity within days of any PoC publication.

Detection Guidance

The following detection content targets the vulnerability class (PHP Object Injection strings and suspicious serialized data in web traffic). These rules should be tuned to the environment and validated once a confirmed PoC or vendor advisory is published.

Sigma Rule

title: PHP Object Injection Attempt Against Supsystic Ultimate Maps (CVE-2026-73376)
id: 6d2b4f1a-9c7e-4f0e-9b3a-7c9a2f5e6d41
status: experimental
description: Detects HTTP requests containing PHP serialized object tokens and references to the Supsystic product, consistent with attempts to exploit CVE-2026-73376.
author: Valters IT Threat Intelligence
date: 2026/01/01
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2026-73376
logsource:
    category: webserver
    product: generic
detection:
    selection_serialized:
        c-uri|contains|base64decode:
            - 'O:'                      # raw PHP object token
        c-uri|contains:
            - 'Tzo'                     # base64 encoding of "O:"
            - '|O:'                     # PHP session-style serialized token
    selection_vendor_uri:
        c-uri|contains:
            - 'supsystic'
    condition: selection_serialized and selection_vendor_uri
falsepositives:
    - Legitimate application traffic that serializes user-provided data
    - Base64-encoded non-object data coincidentally containing the token bytes
level: high

YARA Rule

rule CVE_2026_73376_Ultimate_Maps_PHP_Object_Injection
{
    meta:
        author      = "Valters IT Threat Intelligence"
        description = "Detects serialized PHP object payloads and payload artifacts consistent with CVE-2026-73376 exploitation"
        cve         = "2026-73376"
        reference   = "https://nvd.nist.gov/vuln/detail/CVE-2026-73376"
    strings:
        $php_obj_raw  = /O:\d{1,6}:"[A-Za-z_][A-Za-z0-9_\\]*"/ ascii
        $php_obj_num  = /O:\d{1,6}:/ ascii
        $php_obj_b64  = "Tzo" ascii                    // base64("O:")
        $magic_wakeup = "__wakeup" ascii
        $magic_destr  = "__destruct" ascii
        $vendor_name  = "supsystic" ascii nocase
    condition:
        any of ($php_obj_raw, $php_obj_num, $php_obj_b64)
        and any of ($magic_wakeup, $magic_destr, $vendor_name)
}

Suricata IDS Rule

alert http any any -> $HOME_NET any ( \
  msg:"CVE-2026-73376 Attempted PHP Object Injection - Ultimate Maps by Supsystic < 1.5.0"; \
  flow:established,to_server; \
  http.request_body; content:"O:"; fast_pattern; \
  pcre:"/O:\d{1,6}:\"/"; \
  http.uri; content:"supsystic"; nocase; \
  classtype:attempted-admin; \
  sid:2026073376; rev:1; \
  reference:cve,2026-73376;)

Elastic Detection

any where event.category == "web"
  and (
    url.query like "*O:*"
    or url.query like "*Tzo*"
    or (url.query like "*base64*" and url.query like "*O:*")
    or request.body.content like "*O:*"
    or request.body.content like "*Tzo*"
  )
  and (
    url.path like "*supsystic*"
    or url.query like "*supsystic*"
  )

Splunk SPL Query

index=web OR index=proxy
  sourcetype=access_combined OR sourcetype=pan:traffic
| regex _raw="(?i)(?:supsystic)"
| regex _raw="(?:O:[0-9]{1,6}:\"|Tzo[0-9])"
| eval phase="php_object_injection_attempt"
| stats count earliest(_time) as first_seen latest(_time) as last_seen
        values(uri) as uris values(method) as methods values(response) as statuses
        by src_ip dest_host phase
| where count >= 1
| sort - count, dest_host

Wazuh OSSEC Rule

<group name="web,">
  <rule id="100736" level="12">
    <if_sid>31122</if_sid>
    <regex>O:[0-9]{1,6}:"</regex>
    <regex offset="contains">supsystic</regex>
    <description>CVE-2026-73376 - PHP Object Injection attempt detected against Ultimate Maps by Supsystic</description>
    <group>cve-2026-73376,php_object_injection,supsystic,</group>
    <mitre>
      <id>T1190</id>
    </mitre>
  </rule>
</group>

Mitigation & Patch Guidance

Patch status. Patch confidence is 0/4 — UNPATCHED. No vendor fix, commit, or advisory has been identified from any tracked source. The NVD description defines the vulnerable range as < 1.5.0; operators should prepare to upgrade to 1.5.0 (or later) once Supsystic publishes the fixed build. Until then, no official code-level remediation exists.

1) Immediate mitigations (protect while unpatched):

• Deploy WAF/IPS rules (e.g., the Suricata rule above) to block requests containing PHP serialized object tokens (O:\d+:") and base64-encoded variants (Tzo) directed at any Supsystic path.
• If the Ultimate Maps plugin is not business-critical, disable or remove it entirely; this eliminates the attack surface.
• If it must remain enabled, restrict network access to the plugin's administrative and data-processing functionality via access-control lists, VPN, or source-IP allow-listing.
• Increase logging verbosity for web-server access logs and application logs; feed output to the SIEM detections above.
• Harden the web server: run PHP-FPM under a dedicated low-privilege account, enable open_basedir, and set disable_functions to block system, exec, passthru, shell_exec, popen, and proc_open where application compatibility allows.

2) Patch / upgrade steps (when available):

• Monitor Supsystic's official changelog and the WordPress plugin/software repository for a 1.5.0 release.
• Test the upgrade in a staging environment before production deployment.
• Upgrade to 1.5.0 or later, then verify the plugin version string and re-run the detection rules to confirm no residual exposure.
• If the vendor does not respond in a timely manner, consider replacing Ultimate Maps with an actively maintained alternative.
• Establish a rollback plan (database dump and file snapshot) before applying any upgrade.

3) Long-term hardening:

• Adopt a policy of replacing PHP unserialize() with safe structured formats (e.g., json_decode) in all application code; forbid untrusted deserialization outright.
• Maintain a software inventory and automated vulnerability scanning. Until a patch is confirmed, treat any instance of Ultimate Maps < 1.5.0 as a standing critical finding and re-scan on a weekly basis.
• Subscribe to CVE feeds, the CISA KEV catalog, and vendor security notifications so that if the vulnerability is added to CISA KEV or exploited in the wild, response can be immediate.
• Regular, tested offline backups and documented incident-response procedures for web-shell and PHP-Object-Injection incidents.

References

1. NVD Entry for CVE-2026-73376 — https://nvd.nist.gov/vuln/detail/CVE-2026-73376
2. MITRE CWE-502 (Deserialization of Untrusted Data) — https://cwe.mitre.org/data/definitions/502.html
3. CISA Known Exploited Vulnerabilities Catalog — https://www.cisa.gov/known-exploited-vulnerabilities-catalog (currently no KEV listing for CVE-2026-73376)
4. FIRST EPSS — https://www.first.org/epss/ (no EPSS score assigned at the time of writing)
5. NVD CVSS v3.1 Calculator — https://nvd.nist.gov/vuln-metrics/cvss/v3-calculator?vector=AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

No vendor advisory, researcher blog post, or threat-actor campaign referencing CVE-2026-73376 was identified in the tracked sources at the time of writing. Exploit-in-the-wild evidence: none. All detection artifacts and attacker-step descriptions presented above are derived from the vulnerability class (CWE-502) and the official CVSS/NVD metadata; specific implementation details remain unavailable until Supsystic publishes further disclosure.