CVE-2026-48788
Remark42: Cross-Site Scripting (XSS) on /api/v1/img via content-type spoofing
Description
Remark42 is a self-hosted comment engine for blogs, articles, or any other place where readers can add comments. Versions 1.6.0 through 1.15.0 contain a Cross-Site Scripting (XSS) vulnerability exploitable through content-type spoofing. The Remark42 image proxy fetches an arbitrary remote URL and re-serves the response from Remark42's own origin. During the download phase, the proxy determines whether the resource is an image by inspecting only the Content-Type header advertised by the remote server, never examining the actual bytes; during the serving phase, it instead derives the response Content-Type by sniffing those bytes with http.DetectContentType. An attacker can exploit this inconsistency by hosting a URL that advertises Content-Type: image/png while returning an HTML/JavaScript body: the download check accepts it as an image, the serving path sniffs the body and emits Content-Type: text/html, and the browser renders the attacker-controlled HTML/JavaScript as a document within Remark42's origin. Exploitation requires no Remark42 account on the target instance; the attacker only needs to host the malicious upstream URL and deliver the proxy link to a victim by any means, such as email, direct message, or a link on another website. This issue has been fixed in version 1.16.0.
INFO
Published Date :
June 17, 2026, 1:20 p.m.
Last Modified :
Oct. 25, 2026, 11:10 p.m.
Remotely Exploit :
Yes !
Source :
[email protected]
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | |||||
| CVSS 3.0 | HIGH | MITRE-CVE | ||||
| CVSS 3.0 | HIGH | [email protected] |
Solution
- Update Remark42 to version 1.16.0 or later.
- Configure the image proxy to use stricter content validation.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-48788.
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-48788 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-48788
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-48788 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-48788 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
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CVE Translated by [email protected]
Oct. 25, 2026
Action Type Old Value New Value Added Translation Title: remark42 de umputun, Description: Remark42 es un motor de comentarios autoalojado para blogs, artículos o cualquier otro lugar donde los lectores puedan añadir comentarios. Las versiones 1.6.0 a la 1.15.0 contienen una vulnerabilidad de Cross-Site Scripting (XSS) explotable a través de la suplantación de tipo de contenido. El proxy de imágenes de Remark42 obtiene una URL remota arbitraria y vuelve a servir la respuesta desde el propio origen de Remark42. Durante la fase de descarga, el proxy determina si el recurso es una imagen inspeccionando solo el encabezado Content-Type anunciado por el servidor remoto, sin examinar nunca los bytes reales; durante la fase de servicio, en su lugar, deriva el Content-Type de la respuesta detectando esos bytes con http.DetectContentType. Un atacante puede explotar esta inconsistencia alojando una URL que anuncia Content-Type: image/png mientras devuelve un cuerpo HTML/javascript_disabled: la verificación de descarga lo acepta como una imagen, la ruta de servicio detecta el cuerpo y emite Content-Type: text/html, y el navegador renderiza el HTML/JavaScript controlado por el atacante como un documento dentro del origen de Remark42. La explotación no requiere una cuenta de Remark42 en la instancia objetivo; el atacante solo necesita alojar la URL maliciosa de origen y entregar el enlace del proxy a una víctima por cualquier medio, como correo electrónico, mensaje directo o un enlace en otro sitio web. Este problema ha sido solucionado en la versión 1.16.0. -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Jun. 17, 2026
Action Type Old Value New Value Added Reference https://github.com/umputun/remark42/security/advisories/GHSA-4c8j-mgm4-qqvp Added SSVC {'id': 'CVE-2026-48788', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'poc'}, {'automatable': 'no'}, {'technicalImpact': 'partial'}], 'version': '2.0.3', 'timestamp': '2026-06-17T13:19:50.596883Z'} -
New CVE Received by [email protected]
Jun. 17, 2026
Action Type Old Value New Value Added Affected [{'vendor': 'umputun', 'product': 'remark42', 'versions': [{'status': 'affected', 'version': '>= 1.6.0, < 1.16.0'}]}] Added Description Remark42 is a self-hosted comment engine for blogs, articles, or any other place where readers can add comments. Versions 1.6.0 through 1.15.0 contain a Cross-Site Scripting (XSS) vulnerability exploitable through content-type spoofing. The Remark42 image proxy fetches an arbitrary remote URL and re-serves the response from Remark42's own origin. During the download phase, the proxy determines whether the resource is an image by inspecting only the Content-Type header advertised by the remote server, never examining the actual bytes; during the serving phase, it instead derives the response Content-Type by sniffing those bytes with http.DetectContentType. An attacker can exploit this inconsistency by hosting a URL that advertises Content-Type: image/png while returning an HTML/JavaScript body: the download check accepts it as an image, the serving path sniffs the body and emits Content-Type: text/html, and the browser renders the attacker-controlled HTML/JavaScript as a document within Remark42's origin. Exploitation requires no Remark42 account on the target instance; the attacker only needs to host the malicious upstream URL and deliver the proxy link to a victim by any means, such as email, direct message, or a link on another website. This issue has been fixed in version 1.16.0. Added CVSS V3 AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:L/A:N Added CWE CWE-79 Added CWE CWE-436 Added Reference https://github.com/umputun/remark42/commit/78d6de6bce1e961f023969da3ec8a00dd80c9ae8 Added Reference https://github.com/umputun/remark42/releases/tag/v1.16.0 Added Reference https://github.com/umputun/remark42/security/advisories/GHSA-4c8j-mgm4-qqvp