Remark42: Cross-Site Scripting (XSS) on /api/v1/img via content-type spoofing_CVE-2026-48788

{
    "lastseen": "",
    "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.",
    "published": "2026-06-16T22:29:38.877Z",
    "modified": "2026-06-16T22:29:38.877Z",
    "type": "cve",
    "title": "Remark42: Cross-Site Scripting (XSS) on /api/v1/img via content-type spoofing",
    "source": "GitHub_M",
    "references": "https://github.com/umputun/remark42/security/advisories/GHSA-4c8j-mgm4-qqvp\nhttps://github.com/umputun/remark42/commit/78d6de6bce1e961f023969da3ec8a00dd80c9ae8\nhttps://github.com/umputun/remark42/releases/tag/v1.16.0",
    "id": "CVE-2026-48788",
    "bulletinFamily": "",
    "cwe": [
        "CWE-79",
        "CWE-436"
    ],
    "cvelist": null,
    "sourceData": "umputun remark42 >= 1.6.0, < 1.16.0",
    "sourceHref": "",
    "cvss": {
        "score": 8.2,
        "severity": "HIGH",
        "vector": "CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:L/A:N",
        "version": "3.0"
    },
    "cvss2": [],
    "cvss3": {
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        "baseScore": 0,
        "baseSeverity": "",
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        "privilegesRequired": "",
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        "confidentialityImpact": "",
        "integrityImpact": "",
        "availabilityImpact": "",
        "cvssV3": {
            "version": "",
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            "baseScore": 0,
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        }
    },
    "href": "",
    "category_name": "CVE",
    "post_link": "",
    "product": "remark42",
    "version": ">= 1.6.0, < 1.16.0",
    "vendor": "umputun",
    "ai_description": "",
    "ai_severity": "",
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    "ai_score": 0
}