{"id":"CVE-2026-48788","sourceIdentifier":"security-advisories@github.com","published":"2026-06-17T13:20:43.490","lastModified":"2026-06-17T16:28:34.830","vulnStatus":"Deferred","cveTags":[],"descriptions":[{"lang":"en","value":"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":[{"source":"security-advisories@github.com","affectedData":[{"vendor":"umputun","product":"remark42","versions":[{"version":">= 1.6.0, < 1.16.0","status":"affected"}]}]}],"metrics":{"cvssMetricV30":[{"source":"security-advisories@github.com","type":"Secondary","cvssData":{"version":"3.0","vectorString":"CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:L/A:N","baseScore":8.2,"baseSeverity":"HIGH","attackVector":"NETWORK","attackComplexity":"LOW","privilegesRequired":"NONE","userInteraction":"REQUIRED","scope":"CHANGED","confidentialityImpact":"HIGH","integrityImpact":"LOW","availabilityImpact":"NONE"},"exploitabilityScore":2.8,"impactScore":4.7}],"ssvcV203":[{"source":"134c704f-9b21-4f2e-91b3-4a467353bcc0","ssvcData":{"timestamp":"2026-06-17T13:19:50.596883Z","id":"CVE-2026-48788","options":[{"exploitation":"poc"},{"automatable":"no"},{"technicalImpact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}]},"weaknesses":[{"source":"security-advisories@github.com","type":"Secondary","description":[{"lang":"en","value":"CWE-79"},{"lang":"en","value":"CWE-436"}]}],"references":[{"url":"https://github.com/umputun/remark42/commit/78d6de6bce1e961f023969da3ec8a00dd80c9ae8","source":"security-advisories@github.com"},{"url":"https://github.com/umputun/remark42/releases/tag/v1.16.0","source":"security-advisories@github.com"},{"url":"https://github.com/umputun/remark42/security/advisories/GHSA-4c8j-mgm4-qqvp","source":"security-advisories@github.com"},{"url":"https://github.com/umputun/remark42/security/advisories/GHSA-4c8j-mgm4-qqvp","source":"134c704f-9b21-4f2e-91b3-4a467353bcc0"}]}