# CVE-2026-48788

## Summary

- **CVE ID:** CVE-2026-48788
- **Severity:** HIGH
- **CVSS Score:** 8.2 (CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:L/A:N)
- **CWE:** CWE-79, CWE-436
- **Published:** Jun 16, 2026
- **Last Modified:** Jun 20, 2026

## 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.

## Affected Products

- umputun — remark42 (>= 1.6.0, < 1.16.0)

## References

- [CNA](https://github.com/umputun/remark42/security/advisories/GHSA-4c8j-mgm4-qqvp)
- [CNA](https://github.com/umputun/remark42/commit/78d6de6bce1e961f023969da3ec8a00dd80c9ae8)
- [CNA](https://github.com/umputun/remark42/releases/tag/v1.16.0)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.25%
- **EPSS Percentile:** 16.0

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-11._