{
  "affected": [
    {
      "ranges": [
        {
          "database_specific": {
            "extracted_events": [
              {
                "introduced": "1.6.0"
              },
              {
                "fixed": "1.16.0"
              }
            ],
            "source": "AFFECTED_FIELD"
          },
          "events": [
            {
              "introduced": "71dcb13a7192bfdf311ee276d54ea54a12653ee7"
            },
            {
              "fixed": "556e0a70d5bcd629939b1f955c3fd3f94b03c18f"
            }
          ],
          "repo": "https://github.com/umputun/remark42",
          "type": "GIT"
        }
      ]
    }
  ],
  "aliases": [
    "GHSA-4c8j-mgm4-qqvp"
  ],
  "database_specific": {
    "cna_assigner": "GitHub_M",
    "cwe_ids": [
      "CWE-436",
      "CWE-79"
    ],
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/48xxx/CVE-2026-48788.json"
  },
  "details": "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.",
  "id": "CVE-2026-48788",
  "modified": "2026-07-15T01:49:08.710090886Z",
  "published": "2026-06-16T22:29:38.877Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/umputun/remark42/releases/tag/v1.16.0"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/48xxx/CVE-2026-48788.json"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/umputun/remark42/security/advisories/GHSA-4c8j-mgm4-qqvp"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-48788"
    },
    {
      "type": "FIX",
      "url": "https://github.com/umputun/remark42/commit/78d6de6bce1e961f023969da3ec8a00dd80c9ae8"
    }
  ],
  "schema_version": "1.8.0",
  "severity": [
    {
      "score": "CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Remark42: Cross-Site Scripting (XSS) on /api/v1/img via content-type spoofing"
}