GHSA-5f64-7vfc-rcx6 CVE-2026-45011

Apostrophe has stored XSS via javascript: URL in Image Widget Link

High npm

Severity: 7.3 / 10; High · CVSS 3.1
Exploit chance (EPSS): 0.27%; Chance of exploitation in the next 30 days. Higher than 18.91% of scored vulnerabilities.
Known exploited: No; Not in CISA's catalog
Weakness: CWE-116 Improper Encoding or Escaping of Output; CWE-79 Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Fix: None yet; No fixed version published

Description

Summary

A stored cross-site scripting vulnerability was identified in the image widget functionality. A user with the Editor role can configure an image widget link to use a javascript: URL payload.

Because editors have permission to publish pages, the malicious widget can be published to the live site. When another user, including an administrator or public visitor, clicks the affected image/link, arbitrary JavaScript executes in the victim’s browser.

Affected Version

ApostropheCMS (tested on version: v4.29.0)

Steps to Reproduce

Precondition Ensure at least one image exists in the media library.

If the media library is empty:

Log in as an Editor.
Open the media library.
Upload any JPG or PNG image.
Set any title, for example Probe image.
Publish the image and close the media manager.

Exploitation Steps

Log in as an Editor.
Open the home page.
Enable edit mode for the page.
In the main content area, click Add content.
Select the Image widget.
Choose any existing image from the image picker and save/select it.
Open the image widget settings.
Locate the Link to field and change it to URL.
In the URL field, enter: javascript:alert(document.domain) <img width="1249" height="979" alt="image" src="https://github.com/user-attachments/assets/c7f77177-1711-461d-b9bd-14292a6996d5" />
Save the image and click on Update.
As another user, such as an administrator or guest, open the published page and click the linked image.
Observe that the JavaScript payload executes. <img width="1267" height="1034" alt="image" src="https://github.com/user-attachments/assets/a80484b4-873a-47c1-8682-84626523008a" />

Note: This attack can also be performed by a Contributor. However, because contributors cannot publish content directly, the malicious image widget remains in the draft version and is only visible to users with access to review drafts, such as administrators or editors.

If an administrator reviews and approves/publishes the affected draft, the stored XSS becomes part of the live page and can then affect all users who interact with the malicious image link.

Impact

Successful exploitation allows an Editor to store a JavaScript payload in published page content. When a victim clicks the affected image link, the payload executes in the victim’s browser.

This may allow an attacker to:

perform actions in the context of an authenticated administrator
access sensitive information available in the CMS interface
modify page content or configuration
conduct phishing attacks within the trusted site
compromise visitors who interact with the published image link

Recommendation

Validate and sanitize all user-supplied URLs used in widget link fields.

Specifically:

Reject dangerous URL schemes such as javascript:, data:, and other executable schemes.
Allow only safe protocols such as http:, https:, mailto:, and relative URLs where appropriate.
Normalize and validate URLs server-side before storage.
Encode rendered URLs safely in templates.
Consider applying a strict Content Security Policy to reduce the impact of XSS.

Affected versions

npm

Package	Vulnerable	Fixed in
apostrophe	1 listed versions	No fix yet

How to fix

No fixed version has been published yet. Until one is, remove or replace the package, or turn off or isolate the affected feature. This page updates when a fix ships.

Severity breakdown

CVSS 3.1 7.3

CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:N

Attack vector: Network
Attack complexity: Low
Privileges required: Low
User interaction: Required
Scope: Unchanged
Confidentiality: High
Integrity: High
Availability: None

Weakness

CWE-116: Improper Encoding or Escaping of Output

The product prepares a structured message for communication with another component, but encoding or escaping of the data is either missing or done incorrectly. As a result, the intended structure of the message is not preserved.

How to prevent it

Architecture and Design: Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. For example, consider using the ESAPI Encoding control [REF-45] or a similar tool, library, or framework. These will help the programmer encode outputs in a manner less prone to error. Alternately, use built-in functions, but consider using wrappers in case those functions are discovered to have a vulnerability.
Architecture and Design: If available, use structured mechanisms that automatically enforce the separation between data and code. These mechanisms may be able to provide the relevant quoting, encoding, and validation automatically, instead of relying on the developer to provide this capability at every point where output is generated. For example, stored procedures can enforce database query structure and reduce the likelihood of SQL injection.
Architecture and Design, Implementation: Understand the context in which your data will be used and the encoding that will be expected. This is especially important when transmitting data between different components, or when generating outputs that can contain multiple encodings at the same time, such as web pages or multi-part mail messages. Study all expected communication protocols and data representations to determine the required encoding strategies.
Architecture and Design: In some cases, input validation may be an important strategy when output encoding is not a complete solution. For example, you may be providing the same output that will be processed by multiple consumers that use different encodings or representations. In other cases, you may be required to allow user-supplied input to contain control information, such as limited HTML tags that support formatting in a wiki or bulletin board. When this type of requirement must be met, use an extremely strict allowlist to limit which control sequences can be used. Verify that the resulting syntactic structure is what you expect. Use your normal encoding methods for the remainder of the input.
Architecture and Design: Use input validation as a defense-in-depth measure to reduce the likelihood of output encoding errors (see CWE-20).
Requirements: Fully specify which encodings are required by components that will be communicating with each other.
Implementation: When exchanging data between components, ensure that both components are using the same character encoding. Ensure that the proper encoding is applied at each interface. Explicitly set the encoding you are using whenever the protocol allows you to do so.

CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.

How to prevent it

Architecture and Design: Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid [REF-1482]. Examples of libraries and frameworks that make it easier to generate properly encoded output include Microsoft's Anti-XSS library, the OWASP ESAPI Encoding module, and Apache Wicket.
Implementation, Architecture and Design: Understand the context in which your data will be used and the encoding that will be expected. This is especially important when transmitting data between different components, or when generating outputs that can contain multiple encodings at the same time, such as web pages or multi-part mail messages. Study all expected communication protocols and data representations to determine the required encoding strategies. For any data that will be output to another web page, especially any data that was received from external inputs, use the appropriate encoding on all non-alphanumeric characters. Parts of the same output document may require different encodings, which will vary depending on whether the output is in the: HTML body Element attributes (such as src="XYZ") URIs JavaScript sections Cascading Style Sheets and style property etc. Note that HTML Entity Encoding is only appropriate for the HTML body. Consult the XSS Prevention Cheat Sheet [REF-724] for more details on the types of encoding and escaping that are needed.
Architecture and Design, Implementation: Understand all the potential areas where untrusted inputs can enter your software: parameters or arguments, cookies, anything read from the network, environment variables, reverse DNS lookups, query results, request headers, URL components, e-mail, files, filenames, databases, and any external systems that provide data to the application. Remember that such inputs may be obtained indirectly through API calls.
Architecture and Design: For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely. Then, these modified values would be submitted to the server.
Architecture and Design: If available, use structured mechanisms that automatically enforce the separation between data and code. These mechanisms may be able to provide the relevant quoting, encoding, and validation automatically, instead of relying on the developer to provide this capability at every point where output is generated.
Implementation: Use and specify an output encoding that can be handled by the downstream component that is reading the output. Common encodings include ISO-8859-1, UTF-7, and UTF-8. When an encoding is not specified, a downstream component may choose a different encoding, either by assuming a default encoding or automatically inferring which encoding is being used, which can be erroneous. When the encodings are inconsistent, the downstream component might treat some character or byte sequences as special, even if they are not special in the original encoding. Attackers might then be able to exploit this discrepancy and conduct injection attacks; they even might be able to bypass protection mechanisms that assume the original encoding is also being used by the downstream component. The problem of inconsistent output encodings often arises in web pages. If an encoding is not specified in an HTTP header, web browsers often guess about which encoding is being used. This can open up the browser to subtle XSS attacks.
Implementation: With Struts, write all data from form beans with the bean's filter attribute set to true.
Implementation: To help mitigate XSS attacks against the user's session cookie, set the session cookie to be HttpOnly. In browsers that support the HttpOnly feature (such as more recent versions of Internet Explorer and Firefox), this attribute can prevent the user's session cookie from being accessible to malicious client-side scripts that use document.cookie. This is not a complete solution, since HttpOnly is not supported by all browsers. More importantly, XmlHttpRequest and other powerful browser technologies provide read access to HTTP headers, including the Set-Cookie header in which the HttpOnly flag is set.
Implementation: Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue." Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright. When dynamically constructing web pages, use stringent allowlists that limit the character set based on the expected value of the parameter in the request. All input should be validated and cleansed, not just parameters that the user is supposed to specify, but all data in the request, including hidden fields, cookies, headers, the URL itself, and so forth. A common mistake that leads to continuing XSS vulnerabilities is to validate only fields that are expected to be redisplayed by the site. It is common to see data from the request that is reflected by the application server or the application that the development team did not anticipate. Also, a field that is not currently reflected may be used by a future developer. Therefore, validating ALL parts of the HTTP request is recommended. Note that proper output encoding, escaping, and quoting is the most ef
Architecture and Design: When the set of acceptable objects, such as filenames or URLs, is limited or known, create a mapping from a set of fixed input values (such as numeric IDs) to the actual filenames or URLs, and reject all other inputs.
Operation: Use an application firewall that can detect attacks against this weakness. It can be beneficial in cases in which the code cannot be fixed (because it is controlled by a third party), as an emergency prevention measure while more comprehensive software assurance measures are applied, or to provide defense in depth [REF-1481].
Operation, Implementation: When using PHP, configure the application so that it does not use register_globals. During implementation, develop the application so that it does not rely on this feature, but be wary of implementing a register_globals emulation that is subject to weaknesses such as CWE-95, CWE-621, and similar issues.

References

Advisories

nvd.nist.gov/vuln/detail/CVE-2026-45011

Packages

github.com/apostrophecms/apostrophe

Timeline

May 14, 2026 Published
Oct 26, 2026 Last updated by the source
Oct 31, 2026 Latest EPSS score

Advisory	Severity	Why it's related
GHSA-86wm-68pq-5jwq ApostropheCMS: Unauthenticated resource exhaustion via pre-auth aposBigUpload processing in @apostrophecms/import-export	High	Also affects apostrophe
GHSA-653j-g8j7-gh54 ApostropheCMS: No Attempt Throttling on Authenticated Password-Change Endpoint Enables Unlimited Current-Password Guessing	Medium	Also affects apostrophe
GHSA-vwwx-px9w-crrc ApostropheCMS: Missing Authorization on Notification PATCH/DELETE Endpoints	Low	Also affects apostrophe
GHSA-vmxh-77cw-65j7 ApostropheCMS: Authenticated Object-Level Authorization Bypass in exist-in-locale Reveals Restricted Localized Draft Identifiers	Medium	Also affects apostrophe
GHSA-m2m5-rw3w-cwmj ApostropheCMS: Client-side Prototype Pollution in apos.http.parseQuery leading to DOM-based XSS against authenticated users	Medium	Also affects apostrophe
GHSA-gqh3-7856-rjjg ApostropheCMS: :_id/locales REST route omits the public-API authorization gate its sibling read routes enforce (unauthenticated doc-existence + locale metadata disclosure)	Medium	Also affects apostrophe
GHSA-hhvr-8m24-qqr3 ApostropheCMS: Cross-domain session token in URL confers session takeover	Medium	Also affects apostrophe
GHSA-j5rq-xfvr-p969 ApostropheCMS: Authenticated projection-exclusion prototype-member deletion in @apostrophecms/db-connect causes process-wide denial of service	High	Also affects apostrophe

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