CVE-2026-1885: Authenticated Contributor Stored XSS in Slideshow Wp (<= 1.1) — What WordPress Site Owners Need to Know

Published: 2026-02-12 · Author: Hong Kong Security Expert · Tags: WordPress, XSS, CVE-2026-1885, WAF, plugin security

TL;DR — A stored cross-site scripting (XSS) vulnerability (CVE-2026-1885) was disclosed in the Slideshow Wp WordPress plugin (versions <= 1.1). An authenticated user with Contributor privileges can inject a malicious payload via the shortcode attribute sswpid in the sswp-slide shortcode. The payload is stored and later rendered to site visitors, potentially enabling session theft, content manipulation, or other client-side attacks. If you run this plugin and cannot immediately update or remove it, apply the mitigations and WAF rules in this guide to reduce risk.

Résumé exécutif

On 10 Feb 2026 a stored XSS vulnerability affecting Slideshow Wp (<= 1.1) was publicly documented (CVE-2026-1885). The root cause is insufficient sanitization and/or escaping of the sswpid attribute on the plugin’s sswp-slide shortcode, allowing an authenticated contributor (or higher) to persist HTML/JavaScript that executes when the slideshow is rendered.

• Vulnérabilité : Cross-Site Scripting (XSS) stocké
• Plugin: Slideshow Wp (slug: slideshow-wp)
• Affected versions: ≤ 1.1
• CVE: CVE-2026-1885
• Privilège requis : Contributeur (authentifié)
• CVSS (rapporté) : 6.5 (Moyen)
• Rapporté par : Muhammad Yudha – DJ

This analysis explains why the issue matters, exploitation scenarios, detection steps, immediate mitigations (including WAF/virtual-patch suggestions), developer fixes, and incident response advice from the perspective of a Hong Kong security practitioner.

Pourquoi cette vulnérabilité est importante

Stored XSS is particularly dangerous because the attacker persists a payload that executes in the browsers of visitors who view the affected page. This vulnerability is significant for several reasons:

• Contributor access is common on multi-author sites and community blogs. Contributors can create/edit content that may be published or previewed by editors, which can expose privileged users to injected payloads.
• Le sswpid attribute is intended as an identifier. If it is not validated (for example forced to an integer) and not escaped on output, it becomes an injection point.
• Stored XSS can be used to steal cookies, exfiltrate data, deface content, display phishing forms, or perform client-side actions in the context of higher-privilege users who view the content.

Even if classed as low/medium on some scoring systems, stored XSS must be treated seriously because impact is environment-dependent (site configuration, user roles, CSP, monitoring).

Technical description (what happened)

• The plugin registers a shortcode named sswp-slide. One attribute is sswpid, likely used as an identifier.
• When content containing the shortcode is saved, the value of sswpid is stored without sufficient input sanitization.
• On rendering, the plugin outputs the attribute value into the HTML without proper escaping for attribute or HTML context.
• Because user-supplied characters are not neutralized, a contributor can supply markup or scripts that execute when the page is rendered — a classic stored XSS.

Typical insecure patterns include echoing raw attribute values (e.g., echo $atts['sswpid'];), failing to validate types (not enforcing integer IDs), and not using escaping functions such as esc_attr() ou esc_html().

Scénarios d'exploitation

1. Contributor account abuse:
   An attacker with a Contributor account inserts a shortcode like:

   [sswp-slide sswpid="1">]

   When visitors load the post, the script executes.

2. Social engineering to target editors/admins:
   A contributor submits content for review containing the malicious shortcode; an editor/admin previewing or publishing the content may execute the payload, enabling escalation chains.
3. Distribution de masse :
   If placed on a homepage or popular page, the payload affects many visitors.

Comment détecter si votre site est affecté

1. Vérifiez la version du plugin : WordPress admin → Plugins and confirm Slideshow Wp version. Treat ≤ 1.1 as potentially vulnerable.
2. Search content for the shortcode: In the database, search wp_posts.post_content for occurrences of sswp-slide ou sswpid.

   SELECT ID, post_title, post_type
   FROM wp_posts
   WHERE post_content LIKE '%[sswp-slide%'
   LIMIT 100;

3. Inspect attribute values: Recherchez sswpid values containing characters outside the expected numeric pattern, such as <, >, script, javascript :, percent-encodings like %3C, or event handlers like onerror=.
4. Scan rendered output: Visit pages that include slides and view page source for unescaped <script> tags, or attributes containing scripting content.
5. Run automated scans: Use your chosen website scanner or malware scanner to detect persistent scripts and suspicious content.

Immediate mitigation steps for site owners (fast, practical)

If you cannot patch immediately, perform the following steps to reduce risk:

1. Deactivate or remove the plugin: The safest short-term action is to deactivate Slideshow Wp until a patched release is available.
2. Restrict Contributor role and remove untrusted accounts: Audit users with Contributor or higher roles; demote or remove suspicious or unused accounts.
3. Remove or sanitize all sswp-slide usages: Edit posts/pages and remove suspicious sswpid values or the shortcode entirely.
4. Enable WAF virtual patches (if available): Configure your WAF to block saving or delivering payloads that include suspicious sswpid content (rules suggested below).
5. Implement CSP and browser hardening: Add a Content Security Policy that disallows inline scripts and restricts script sources to reduce impact of injected scripts.
6. Rotate credentials & sessions: If compromise is suspected, force password resets for admins and invalidate sessions.
7. Run malware scans and review logs: Scan for unexpected files or injected scripts and check access logs for suspicious POST requests that saved shortcode content.

Recommended temporary WAF / virtual-patch rules (apply now)

Below are practical, generic WAF rules to mitigate exploitation while you wait for a plugin update. Adapt the patterns to your WAF engine. Test in monitoring mode first.

1) Block POSTs that attempt to save sswp-slide with suspicious content

Match request bodies containing sswp-slide où le sswpid attribute includes scripting or encoded characters.

Pattern (pseudo):
\[sswp-slide[^\]]*sswpid\s*=\s*(?:'|")?\s*[^'"\]\s]*(?:<|%3C|javascript:|data:|onerror=|onload=|&#x)
Action: Block request / Flag as suspicious
    

2) Block responses that contain an unescaped sswpid with suspicious characters

Inspect outgoing HTML for sswpid="…" values that include scripting markers and sanitize or block the response.

Regex (pseudo):
/sswpid\s*=\s*["'][^"']*(<|%3C|script|javascript:|onerror=|onload=)[^"']*["']/i
Action: Strip attribute or replace with safe placeholder, or block response
    

3) Deny inline scripts on pages that include the shortcode

If a page contains the shortcode, enforce response filtering to remove inline <script> blocks on that page.

4) Sanitize common encodings

Block or flag requests where sswpid contains encodings such as < ou <, often used to bypass naive filters.

Note: Apply these rules in monitoring mode first to identify false positives. Log matched requests for incident response and tuning. If your WAF supports parameter-targeted rules (e.g., filtering the contenu_du_post parameter on REST API post-save endpoints), scope rules narrowly to reduce disruption.

Developer fix (how plugin authors should patch this)

Plugin authors should implement the following fixes to permanently close the issue:

1. Validez les types d'entrée : Si sswpid should be numeric, coerce and validate it:

   $atts['sswpid'] = isset($atts['sswpid']) ? intval($atts['sswpid']) : 0;

2. Sanitize attributes on input: Utilisez sanitize_text_field() or stricter validators where appropriate:

   $atts['sswpid'] = isset($atts['sswpid']) ? sanitize_text_field( $atts['sswpid'] ) : '';

3. Échappez la sortie en fonction du contexte :
   • In attributes: echo esc_attr( $atts['sswpid'] );
   • In HTML content: echo esc_html( $value );
   • Si un HTML limité est autorisé, utilisez wp_kses() avec une liste blanche explicite.
4. Use strict whitelisting: Prefer whitelisting acceptable values (e.g., numeric IDs) rather than blacklisting characters.
5. Avoid echoing user-supplied content without escaping: Audit all markup paths where sswpid is used.
6. Ajoutez des tests : Unit tests and fuzzing for shortcode attributes should include cases trying to inject ", <, >, javascript : encodings.

Hardening and best practices for WordPress sites

• Principe du moindre privilège : Assign the minimum role required. Use a content review workflow so only trusted users publish.
• Content filters for untrusted roles: Strip shortcodes or HTML for Contributor-level users, or restrict which shortcodes are allowed for untrusted roles.
• Keep plugins up-to-date: Track vendor security updates and patch promptly after testing.
• Use a WAF: A well-configured WAF can virtual-patch and block attack patterns until a vendor release is available.
• Enforce CSP: A strong Content Security Policy can significantly reduce the impact of XSS by disallowing inline scripts.
• Analyse régulière : Run automated scans and periodic manual reviews to detect stored payloads or suspicious content.
• Review plugin code before install: For plugins that render user-supplied content, check for appropriate escaping and sanitization.

Detecting possible compromise (Indicators of Compromise)

• Inattendu <script> blocks or inline event handlers (onerror, au chargement) in post content.
• Unusual outbound requests from clients visiting your pages (indicative of data exfiltration).
• Admin accounts showing unknown activity after viewing content.
• Suspicious POST requests to REST endpoints with sswp-slide shortcodes and encoded payloads.
• Unexplained changes to homepage or widely visited pages, popup forms, or redirects.

If you find indicators, remove the malicious content, rotate credentials, capture forensic snapshots (files + DB), and perform a full incident response including file integrity checks.

Liste de contrôle de réponse à l'incident (étape par étape)

1. Take an emergency snapshot of the site (files + DB) for forensics.
2. Put the site into maintenance mode if necessary to prevent further damage.
3. Désactivez immédiatement le plugin vulnérable.
4. Remove or sanitize malicious posts/pages (search for sswp-slide and suspicious sswpid values).
5. Rotate admin/staff passwords and force logout for all sessions.
6. Run a full malware scan and a file integrity check.
7. Apply tuned WAF rules as described above; begin in monitoring mode, then move to blocking after tuning.
8. After cleanup, re-enable the plugin only if a patched version is available and you have verified the fix.
9. Perform a post-incident review to determine how contributor access was obtained and close any gaps in your processes.

FAQ

Cette vulnérabilité est-elle exploitable par des visiteurs anonymes ?

No. An authenticated user with at least Contributor privileges is required to inject the payload. The impact occurs when the stored payload is later rendered to any visitor (including anonymous visitors).

Does deactivating the plugin remove stored payloads?

Deactivation typically stops the plugin from rendering the shortcode, which prevents execution, but malicious content may remain in the database. Clean or remove affected post content to permanently eliminate stored XSS payloads.

How long should I keep WAF rules enabled after patching?

Keep the rules enabled for several weeks after patching and monitor logs for blocked attempts. Relax or remove rules only after you are confident the vendor patch eliminates the vulnerability and stored payloads have been cleaned.

Remarques finales

Stored XSS in shortcodes and plugin attributes is a recurring pattern in WordPress. The combination of user-supplied content, insufficient validation, and unsafe rendering creates persistent danger. Apply these core principles:

• Validate input early (whitelist values, not blacklist).
• Escape output for the specific HTML context.
• Limit what untrusted users can submit or render.
• Layer defenses (WAF, CSP, least privilege) so a single failure does not lead to compromise.

If you run Slideshow Wp (<= 1.1), take action today: remove/deactivate the plugin, scrub all occurrences of sswp-slide shortcodes from content, or deploy the WAF virtual-patches described above while you coordinate long-term remediation.

Références

• CVE-2026-1885 — public vulnerability identifier
• Research credit: Muhammad Yudha - DJ