{"id":"CVE-2026-48788","state":"PUBLISHED","title":"Remark42: Cross-Site Scripting (XSS) on /api/v1/img via content-type spoofing","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.","publishedAt":"2026-06-16T22:29:38.877Z","updatedAt":"2026-06-17T13:20:11.543Z","severity":{"score":8.2,"label":"High","version":"3.0","vector":"CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:L/A:N","source":"GitHub_M"},"assigner":"GitHub_M","products":["umputun remark42"],"affected":[{"vendor":"umputun","product":"remark42","versions":[{"version":">= 1.6.0, < 1.16.0","status":"affected"}]}],"references":["https://github.com/umputun/remark42/security/advisories/GHSA-4c8j-mgm4-qqvp","https://github.com/umputun/remark42/commit/78d6de6bce1e961f023969da3ec8a00dd80c9ae8","https://github.com/umputun/remark42/releases/tag/v1.16.0"],"weaknesses":["CWE-79","CWE-436"],"ingestedAt":"2026-10-29T20:12:07.131Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/48xxx/CVE-2026-48788.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-48788","state":"PUBLISHED","datePublished":"2026-06-16T22:29:38.877Z","dateUpdated":"2026-06-17T13:20:11.543Z","assignerShortName":"GitHub_M","assignerOrgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateReserved":"2026-05-22T20:18:20.365Z"},"containers":{"cna":{"title":"Remark42: Cross-Site Scripting (XSS) on /api/v1/img via content-type spoofing","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":[{"vendor":"umputun","product":"remark42","versions":[{"version":">= 1.6.0, < 1.16.0","status":"affected"}]}],"references":[{"url":"https://github.com/umputun/remark42/security/advisories/GHSA-4c8j-mgm4-qqvp","name":"https://github.com/umputun/remark42/security/advisories/GHSA-4c8j-mgm4-qqvp","tags":["x_refsource_CONFIRM"]},{"url":"https://github.com/umputun/remark42/commit/78d6de6bce1e961f023969da3ec8a00dd80c9ae8","name":"https://github.com/umputun/remark42/commit/78d6de6bce1e961f023969da3ec8a00dd80c9ae8","tags":["x_refsource_MISC"]},{"url":"https://github.com/umputun/remark42/releases/tag/v1.16.0","name":"https://github.com/umputun/remark42/releases/tag/v1.16.0","tags":["x_refsource_MISC"]}],"metrics":[{"cvssV3_0":{"attackComplexity":"LOW","attackVector":"NETWORK","availabilityImpact":"NONE","baseScore":8.2,"baseSeverity":"HIGH","confidentialityImpact":"HIGH","integrityImpact":"LOW","privilegesRequired":"NONE","scope":"CHANGED","userInteraction":"REQUIRED","vectorString":"CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:L/A:N","version":"3.0"}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-79","lang":"en","description":"CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')","type":"CWE"}]},{"descriptions":[{"cweId":"CWE-436","lang":"en","description":"CWE-436: Interpretation Conflict","type":"CWE"}]}],"providerMetadata":{"shortName":"GitHub_M","orgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateUpdated":"2026-06-16T22:29:38.877Z"},"source":{"advisory":"GHSA-4c8j-mgm4-qqvp","discovery":"UNKNOWN"}},"adp":[{"title":"CISA ADP Vulnrichment","references":[{"url":"https://github.com/umputun/remark42/security/advisories/GHSA-4c8j-mgm4-qqvp","tags":["exploit"]}],"metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-06-17T13:19:50.596883Z","id":"CVE-2026-48788","options":[{"Exploitation":"poc"},{"Automatable":"no"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-06-17T13:20:11.543Z"}}]}}}