CVE-2026-65553

Executive Summary

CVE-2026-65553 is a critical, unauthenticated Remote Code Execution (RCE) vulnerability affecting the WordPress Spider Analyser (WordPress搜索引擎蜘蛛分析插件) plugin, specifically versions 2.1.3 and earlier. The vulnerability carries a CVSS 3.1 base score of 10.0, indicating maximum severity across confidentiality, integrity, and availability impacts, with a scope change indicating the compromised plugin can affect adjacent resources. Any WordPress site running the Spider Analyser plugin at or below version 2.1.3 is affected, and because the vulnerability requires no authentication, no user interaction, and no special conditions for successful exploitation, it is highly likely to be targeted by automated scanning and mass exploitation campaigns. At the time of this report, no patch, vendor fix, or official workaround is available from any tracked source; the patch confidence rating is 0/4 (UNPATCHED). Organizations using this plugin should treat it as actively dangerous and take immediate mitigation action.

Technical Analysis

The NVD description for CVE-2026-65553 is sparse: "Unauthenticated Remote Code Execution (RCE) in Spider Analyser – WordPress搜索引擎蜘蛛分析插件 <= 2.1.3 versions." Despite the terse description, the vulnerability class is unambiguous. The plugin is classified under CWE-94, "Improper Control of Generation of Code ('Code Injection')", which means the root cause involves the plugin failing to properly sanitize or validate user-supplied input before passing it to a code evaluation mechanism — be that PHP functions such as eval(), assert(), preg_replace() with the /e modifier, call_user_func() with user-controlled callables, or dynamic file inclusion via include()/require().

The functional nature of the plugin is also relevant. The Spider Analyser plugin is designed to log and analyze traffic from search engine spiders and bots (e.g., Googlebot, Bingbot, Baidu Spider). The plugin likely hooks into WordPress's request lifecycle via the init action or a similar hook to inspect user-agent strings and request metadata. Because search engine spiders arrive with varied and unpredictable user-agent strings, plugins of this type frequently capture raw request data into log files or database tables without strict sanitization, believing the data to be low-risk. This is a classic attack surface for unauthenticated RCE: the plugin may store the raw User-Agent header, REMOTE_ADDR, HTTP_REFERER, or other request parameters and later process them through a string-interpolated evaluation or dynamic include. If any of those values are passed to a potentially dangerous PHP function without rigorous filtering, a remote attacker can inject malicious PHP code.

The unauthenticated nature of the flaw means no WordPress account, session, or special capability is required. The attack surface is the WordPress front-end, reachable via the standard HTTP/HTTPS port. The attacker-supplied payload would ride in a standard HTTP request header or request body parameter, making the vulnerability trivial to weaponize with simple HTTP clients such as curl, wget, or scripted tooling. The CVSS vector — AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H — confirms: network-accessible, low attack complexity, no privileges required, no user interaction, and a scope change indicating the compromised component can impact resources beyond its security scope (i.e., the web server, the operating system, or other sites on shared hosting).

Because the plugin is unpatched and no vendor fix exists, the vulnerable code paths remain fully exposed on any installation still running version 2.1.3 or earlier. There is no evidence of public proof-of-concept code at the time of writing, but the severity of this vulnerability class, combined with its trivial exploitation requirements, makes private weaponization highly plausible.

Exploitation Scenarios

The following attack chain describes a realistic end-to-end exploitation scenario for CVE-2026-65553. All steps are based on the technical characteristics implied by the vulnerability class (unauthenticated code injection in a WordPress spider-logging plugin).

Step 1 — Target Identification and Reconnaissance. An attacker begins by scanning the internet for WordPress sites running the Spider Analyser plugin. Because the plugin generates identifiable HTML comments, meta tags, JavaScript file references, or static asset paths in the page source, the attacker can use search engines with dorks (e.g., inurl:"wp-content/plugins/spider-analyser") or broad HTTP scanning with tools like nuclei, wpscan, or bespoke Python scanners to fingerprint the plugin and its version. The attacker then filters results to those reporting version 2.1.3 or an earlier version.

Step 2 — Request Crafting and Trigger. The attacker crafts an HTTP GET or POST request to any publicly accessible endpoint of the WordPress site, targeting the code path where the plugin logs spider activity. The malicious payload is placed in the User-Agent header — the field most likely to be captured verbatim by the plugin's logging mechanism. For a code injection vulnerability of this class, the payload would resemble one of the following patterns: a PHP webshell written to the webroot via file_put_contents() in a string-evaluated context, a base64-encoded command execution chain, or a direct function call to system(), exec(), or shell_exec() containing the attacker's command. Critically, the request requires no authentication cookies, no CSRF tokens, and no special WordPress privileges — the plugin processes the request before any auth checks occur.

Step 3 — Payload Execution. The plugin receives the HTTP request, extracts the User-Agent value, and stores it in its logging pipeline. Because of the missing input sanitization, the user-controlled value is interpolated into a PHP execution context. The payload executes with the permissions of the PHP-FPM or Apache process — typically the www-data user on Linux systems. A common post-exploitation goal is placing a persistent web shell, e.g., writing a PHP file into the WordPress uploads directory or plugin directory. After the request completes, the attacker verifies the shell by requesting the newly created file and receiving a 200 OK response.

Step 4 — Post-Exploitation Impact. Once code execution is confirmed, the attacker can escalate to full site compromise: reading wp-config.php to harvest database credentials, extracting the WordPress authentication keys (AUTH_KEY, SECURE_AUTH_KEY, etc.) to forge authentication cookies, dumping the user database to harvest login credentials, and modifying or deleting site content, themes, and plugins. The RCE runs under the web server user, so the attacker can also attempt privilege escalation to root via kernel exploits, misconfigured sudo rules, or writable system files. On shared hosting environments, the attacker can pivot to other virtual hosts on the same server, fully realizing the "scope change" component of the CVSS vector. The attacker may also inject SEO spam, cryptocurrency miners, or credential-stealing scripts into the site.

Impact Assessment

The CVSS 3.1 base score of 10.0 places this vulnerability at the absolute maximum of the severity scale. The breakdown is as follows: Attack Vector: Network (N) — exploitable remotely over the internet; Attack Complexity: Low (L) — no special conditions or race conditions required; Privileges Required: None (N) — anyone on the internet can trigger the flaw; User Interaction: None (N) — no victim action needed; Scope: Changed (C) — the vulnerability can impact resources beyond the plugin's security authority, i.e., the web server, database, or other co-hosted applications; Confidentiality/Integrity/Availability Impact: High (H) (each) — complete loss of confidentiality (database and file disclosure), integrity (full file and content manipulation), and availability (server shutdown, data destruction, ransomware).

The business impact is severe. For an affected WordPress site, the vulnerability represents total technical compromise. If the site processes e-commerce transactions, customer PII, or business-critical content, the downstream regulatory and financial implications extend beyond the technical outage: data breach notification obligations under GDPR/CCPA/PIPL, reputational damage, and potential legal liability. For a managed WordPress hosting provider, a single unpatched client site running this plugin is an entry point into the shared infrastructure, potentially exposing hundreds or thousands of other tenants.

The blast radius is amplified by the plugin's popularity, if any, among Chinese-language WordPress deployments; the plugin's Chinese name suggests adoption across that demographic. Given the trivial exploitation requirements, automated botnets and vulnerability scanners are expected to weaponize this CVE within days of public disclosure. Because no patch exists at the time of writing, every affected site remains at risk with no remediation path other than deactivation and removal of the plugin. The absence of a vendor fix means the risk is not self-limiting; it will persist indefinitely until a patch is released or the plugin is abandoned.

Detection Guidance

The following detection content is generated based on the vulnerability's expected HTTP-level artifacts, as no public PoC or specific exploit string is known. These rules should be treated as starting points and tuned to the environment.

Sigma Rule

title: WordPress Spider Analyser Plugin RCE - Suspicious User-Agent
id: c67a1f3e-1c95-4a1d-9c3d-234f91a2b451
status: experimental
description: Detects suspicious User-Agent strings targeting WordPress Spider Analyser plugin CVE-2026-65553
author: valtersit.com Threat Intelligence
date: 2026/01/01
tags:
    - attack.initial-access
    - attack.t1190
    - cve.2026.65553
logsource:
    category: webserver
    product: apache
    definition: 'Requires access logs for WordPress sites'
detection:
    selection_uri:
        cs-uri-extension:
            - '*.php'
    selection_ua_eval:
        cs-user-agent|contains:
            - 'eval('
            - 'assert('
            - 'system('
            - 'shell_exec('
            - 'passthru('
            - 'base64_decode('
            - 'file_put_contents('
    selection_ua_webshell:
        cs-user-agent|contains:
            - '.php'
            - '<?php'
            - '$_POST'
            - '$_GET'
            - 'c99'
            - 'r57'
            - 'wso'
    selection_path_plugin:
        cs-uri-stem|contains:
            - '/wp-content/plugins/spider-analyser/'
    condition: selection_uri and selection_path_plugin and (selection_ua_eval or selection_ua_webshell)
    timeframe: 5m
level: high
falsepositives:
    - Security scanners performing legitimate vulnerability checks
    - Malformed search engine bots with unusual characters in UA
fields:
    - c-ip
    - cs-user-agent
    - cs-uri-stem
    - sc-status

YARA Rule

rule WordPress_Spider_Analyser_CVE_2026_65553
{
    meta:
        author = "valtersit.com Threat Intelligence"
        description = "Detects exploit payloads and web shells associated with CVE-2026-65553"
        date = "2026-01-01"
        severity = "critical"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-65553"

    strings:
        $php_func1 = "eval(" ascii wide
        $php_func2 = "assert(" ascii wide
        $php_func3 = "system(" ascii wide
        $php_func4 = "shell_exec(" ascii wide
        $php_func5 = "passthru(" ascii wide
        $php_func6 = "base64_decode(" ascii wide
        $php_func7 = "file_put_contents(" ascii wide
        $php_webshell1 = "<?php" ascii wide
        $php_webshell2 = "c99sh" ascii wide
        $php_webshell3 = "r57shell" ascii wide
        $plugin_marker = "spider-analyser" ascii wide nocase
        $payload_marker = "User-Agent" ascii wide nocase

    condition:
        uint16(0) == 0x0A0D and
        ( $plugin_marker or $payload_marker ) and
        2 of ( $php_func* ) and
        ( $php_webshell1 or 1 of ( $php_webshell2, $php_webshell3 ) )
}

Suricata IDS Rule

alert http any any -> $HOME_NET any (
    msg:"CVE-2026-65553 WordPress Spider Analyser RCE Attempt";
    flow:established,to_server;
    http.uri;
    content:"wp-content/plugins/spider-analyser";
    http.user_agent;
    content:"eval("; nocase;
    content:"assert("; distance:0; nocase;
    content:"system("; distance:0; nocase;
    content:"shell_exec"; distance:0; nocase;
    content:"passthru"; distance:0; nocase;
    content:"base64_decode"; distance:0; nocase;
    content:"file_put_contents"; distance:0; nocase;
    content:"<?php"; distance:0; nocase;
    classtype:attempted-admin;
    sid:20266553;
    rev:1;
    metadata:created_at 2026_01_01, updated_at 2026_01_01, cve CVE-2026-65553;
)

Note: The OR logic within a single Suricata rule using content directives requires the flowbits or multiple alert rules. For production use, split each content match into its own rule, or use the pcre option with alternation. Example alternative:

alert http any any -> $HOME_NET any (
    msg:"CVE-2026-65553 WordPress Spider Analyser UA payload";
    flow:established,to_server;
    http.uri;
    content:"wp-content/plugins/spider-analyser";
    pcre:"/(?:eval|assert|system|shell_exec|passthru|base64_decode|file_put_contents)\s*\(/iU";
    reference:cve,2026-65553;
    classtype:attempted-admin;
    sid:20266554;
    rev:1;
)

Elastic Detection

// EQL query for Elastic Security - detect exploitation attempts against the plugin
sequence by source.ip
  with maxspan=5m
  [network where
     dns.question.name : "*spider-analyser*" or
     url.path : "*wp-content/plugins/spider-analyser*"]
  [network where
     // Match payload indicators in the User-Agent header
     url.user_agent : "*eval(*" or
     url.user_agent : "*assert(*" or
     url.user_agent : "*system(*" or
     url.user_agent : "*shell_exec(*" or
     url.user_agent : "*passthru(*" or
     url.user_agent : "*base64_decode(*" or
     url.user_agent : "*file_put_contents(*" or
     url.user_agent : "*<?php*" or
     url.user_agent : "*.php?*"]
  [process where
     // Post-exploitation process creation indicating webshell execution
     process.name : ("php", "php-fpm", "apache2", "httpd")]

Splunk SPL Query

index=web sourcetype=access_combined
| where like(uri_path, "%wp-content/plugins/spider-analyser%")
| where (
      like(user_agent, "%eval(%") OR
      like(user_agent, "%assert(%") OR
      like(user_agent, "%system(%") OR
      like(user_agent, "%shell_exec%") OR
      like(user_agent, "%passthru%") OR
      like(user_agent, "%base64_decode%") OR
      like(user_agent, "%file_put_contents%") OR
      like(user_agent, "%<?php%") OR
      like(user_agent, "%.php%")
  )
| eval threat_score = case(
     like(user_agent, "%<?php%"), 100,
     like(user_agent, "%eval(%"), 90,
     like(user_agent, "%assert(%"), 90,
     like(user_agent, "%system(%"), 90,
     like(user_agent, "%shell_exec%"), 90,
     like(user_agent, "%passthru%"), 90,
     like(user_agent, "%base64_decode%"), 80,
     like(user_agent, "%file_put_contents%"), 80,
     50)
| search threat_score >= 50
| stats count min(_time) as first_seen max(_time) as last_seen by src_ip, uri_path, user_agent, threat_score
| sort - count
| table first_seen last_seen src_ip uri_path user_agent count threat_score
| rename src_ip as "Source IP", user_agent as "User Agent", uri_path as "URI Path", 
         first_seen as "First Seen", last_seen as "Last Seen", count as "Request Count"

Wazuh OSSEC Rule

<group name="web,wordpress,spider_analyser,rce,">
  <rule id="942009" level="15">
    <decoded_as>web</decoded_as>
    <match>wp-content/plugins/spider-analyser</match>
    <regex>User-Agent: .*(eval\(|assert\(|system\(|shell_exec|passthru|base64_decode|file_put_contents|&lt;\?php).*</regex>
    <description>CVE-2026-65553 - WordPress Spider Analyser plugin RCE exploitation attempt detected</description>
    <group>web_application_attack,rce,wordpress,</group>
    <mitre>
      <id>T1190</id>
    </mitre>
    <cve>CVE-2026-65553</cve>
    <info>Potential unauthenticated remote code execution attempt against WordPress Spider Analyser plugin (version <= 2.1.3). Refer to NVD CVE-2026-65553.</info>
    <options>no_full_log</options>
    <alert>cve.2026.65553</alert>
  </rule>

  <rule id="942010" level="10">
    <if_sid>1023553</if_sid>
    <match>status=200</match>
    <description>CVE-2026-65553 - Possible successful exploitation returned HTTP 200</description>
    <group>web_application_attack,rce,wordpress,</group>
  </rule>
</group>

Mitigation & Patch Guidance

Patch Status: UNPATCHED (0/4 confidence). No patch evidence from any tracked source exists. The NVD description does not reference a fixed version. The Patchstack CNA title indicates versions "<= 2.1.3" are affected, which implies a later version might remediate the flaw, but no such version has been confirmed as available. Treat this as an unpatched, indefinite risk.

Immediate Mitigations (apply within hours):

1. Disable and uninstall the Spider Analyser plugin. This is the single most effective containment measure. Navigate to the WordPress admin dashboard → Plugins → Installed Plugins, find "Spider Analyser" (WordPress搜索引擎蜘蛛分析插件), click "Deactivate", then "Delete". If the site is critical and immediate admin access is not possible, rename the plugin directory on the server via SSH: mv /path/to/wp-content/plugins/spider-analyser /path/to/wp-content/plugins/spider-analyser.disabled. WordPress will cease loading the plugin.
2. If the plugin cannot be removed immediately, block access to its files via web server rules. Add a location block in nginx or a directory deny in Apache that returns 403 for any request containing spider-analyser in the URI. This provides a temporary network-level stopgap, although a robust attacker could still reach the code paths if the plugin handles requests outside its own directory (e.g., via WordPress hooks on the site root). The plugin removal is mandatory.
3. Audit the site for prior compromise. Given the scores of 10.0 and the lack of patch, the window of exposure may span weeks or months. Search the web root for unexpected PHP files created recently, review the WordPress users table for new admin accounts, and check for outbound connections to known scanner IP ranges. Common webshell filenames include random hex strings followed by .php in wp-content/uploads/.
4. Rotate all credentials. This includes WordPress admin passwords, database passwords, FTP/SFTP credentials, and any API keys stored in wp-config.php, on the assumption that the site may have been compromised previously. Also rotate the WordPress salts (AUTH_KEY, SECURE_AUTH_KEY, etc.) to invalidate existing session cookies.

Patch/Upgrade Steps: Monitor the Patchstack advisory feed and the WordPress plugin repository (wordpress.org/plugins) for a patched version of Spider Analyser. Subscribe to CVE notifications for CVE-2026-65553. When a patched version is released, install it immediately after testing in a staging environment. Because the plugin's Chinese-language name suggests it may be distributed via third-party marketplaces or the developer's own site rather than wordpress.org, verification of the vendor's original distribution channel is necessary to ensure the authenticity of any future update. Until a patch is released, do not re-enable the plugin under any circumstances.

Long-Term Hardening:

1. Maintain a strict plugin inventory and update cadence. WordPress plugins are the leading source of critical RCEs. Establish a policy to review the plugin list quarterly, remove abandoned or unused plugins, and enable automatic updates with a testing requirement for all active plugins.
2. Apply a Web Application Firewall (WAF). Deploy a WAF in front of WordPress that includes virtual patching for the CVE-2026-65553. Services like Cloudflare, AWS WAF, or ModSecurity with an updated OWASP Core Rule Set can block the malicious payload signatures (PHP function calls in headers) even without a plugin patch. The Suricata rules above can be converted to WAF rules.
3. Run WordPress under a dedicated non-root user with minimal filesystem permissions. Ensure the web server user (www-data) has write access only to wp-content/uploads and not to the rest of the webroot, limiting the blast radius of any successful RCE.
4. Implement web server-level request filtering. Add a rule to reject HTTP requests with suspicious PHP function names in User-Agent headers, which would block most generic exploitation attempts against this plugin and similar ones.
5. Enable robust logging and alerting. Configure access logs with full User-Agent capture, ship them to a SIEM, and alert on the detection rules provided above. EDR/XDR monitoring on the web server host should watch for unexpected child processes spawned by PHP-FPM.

References

1. NVD Entry for CVE-2026-65553 — https://nvd.nist.gov/vuln/detail/CVE-2026-65553 — Authoritative CVE record with NVD description and CVSS 3.1 vector.
2. CVE Mitre Entry — https://www.cve.org/CVERecord?id=CVE-2026-65553 — CVE ID registration and CNA provenance.
3. Patchstack Vulnerability Database — https://patchstack.com/database/ — CNA for this CVE; advisory page for Spider Analyser WordPress plugin (search CVE-2026-65553).

Threat Actor Campaigns & Exploit-in-the-Wild Evidence: At the time of this report, there is no public evidence of active exploitation campaigns, exploit code, or attacker TTPs targeting CVE-2026-65553, and the EPSS score has not yet been published by FIRST.org. The vulnerability is not listed on the CISA Known Exploited Vulnerabilities (KEV) catalog. However, given the combination of a maximum CVSS score, unauthenticated access, and the absence of a patch, it is almost certain that security researchers and threat actors are actively reverse-engineering the plugin. The risk of an exploit becoming publicly available is assessed as high within the next 30 to 60 days. The CISA KEV catalog should be monitored as the authoritative source for confirmation of active in-the-wild use; should CISA add this CVE to the KEV list, federal agencies will be mandatorily required to remediate within the specified timeline (typically 14 days for critical-severity CVEs).