{"id":"CVE-2026-48788","aliases":["GHSA-4c8j-mgm4-qqvp","GO-2026-5804"],"url":"https://o3.security/vulnerability/CVE-2026-48788","summary":"Remark42: Cross-Site Scripting (XSS) on /api/v1/img via content-type spoofing","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.","published":"2026-06-16T22:29:38.877Z","modified":"2026-08-12T03:51:45.940758568Z","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"},"epss":{"score":0.00247,"percentile":0.16089,"asOf":"2026-08-11"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"Go","name":"github.com/umputun/remark42","fixedVersion":"1.16.0"}],"fix":{"url":"https://github.com/umputun/remark42/commit/78d6de6bce1e961f023969da3ec8a00dd80c9ae8","label":"umputun/remark42@78d6de6"},"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"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-12T03:51:45.940758568Z"}}