CVE-2026-48788
Remark42: Cross-Site Scripting (XSS) on /api/v1/img via content-type spoofing
- Published
- Updated
- Reserved
- Assigned by
- GitHub_M
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.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| GitHub_MCNA (assigner) | 3.0 | High8.2 | CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:L/A:N |
| NVDNVD · Deferred | 3.0 | High8.2 | CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:L/A:N |
- EPSS (exploitation in 30 days)
- 0.31% · top 76% of all CVEs (6 Nov 2026)
- CISA SSVC
- Exploitation: poc · Automatable: no · Technical impact: partial
The list uses the assigner's score when there is one, then CISA's, then NVD's: High 8.2.
Weakness
Affected products
Affected packages
From reviewed advisories of the GitHub Advisory Database.
- Gogithub.com/umputun/remark42GHSA-4c8j-mgm4-qqvp (opens in a new tab)
References (3)
- https://github.com/umputun/remark42/security/advisories/GHSA-4c8j-mgm4-qqvp (opens in a new tab)x_refsource_CONFIRMexploit
- https://github.com/umputun/remark42/commit/78d6de6bce1e961f023969da3ec8a00dd80c9ae8 (opens in a new tab)x_refsource_MISC
- https://github.com/umputun/remark42/releases/tag/v1.16.0 (opens in a new tab)x_refsource_MISC
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisory GHSA-4c8j-mgm4-qqvp (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
Badge for a README or a ticket
[](https://trackcve.app/cve/CVE-2026-48788)Record last updated .