Vulnerability in github.com/umputun/remark42 (CVE-2026-48788)
Summary
Vulnerability in github.com/umputun/remark42 (CVE-2026-48788). Confidential information can be exposed externally. Exploitable via http.DetectContentType. Mitigation: upgrade to 1.16.0 or later.
Original description
The description as published by the source.
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.
Source: NIST National Vulnerability Database NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-48788 has been found in github.com/umputun/remark42.
Attackers can target a specific entry point like http.DetectContentType over the network to misuse the product.
Confidential information can be exposed externally. CVSS score: 8.2/10.
What to do: upgrade github.com/umputun/remark42 to 1.16.0 or later.
If unsure, ask your IT team or search "github.com/umputun/remark42 CVE-2026-48788" on the vendor's site.
CVE-2026-48788 (github.com/umputun/remark42) — CWE-436 / CVSS v3 8.2
Attack vector: remote (network-reachable) / unauthenticated
Attack surface: http.DetectContentType / rest.SafeImgContentType
Patched: 1.16.0 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
A vulnerability (CWE-436) exists in github.com/umputun/remark42. Attackers reach the vulnerable code path via http.DetectContentType without authentication.
Check the vendor advisory for the affected versions of github.com/umputun/remark42. Attack surface: http.DetectContentType / rest.SafeImgContentType.
Severity: High (CVSS 8.2/10). Confidential information can be exposed externally.
Update to 1.16.0.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'github.com/umputun/remark42' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
grep -r 'github.com/umputun/remark42' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
github.com/umputun/remark42を grep し、稼働しているサービス・バージョンを把握する。 -
2Apply patch patch
Upgrade github.com/umputun/remark42 to 1.16.0ステージング環境で 1.16.0 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
-
3Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
References
- advisory github.com
- advisory nvd.nist.gov
- advisory github.com
- package github.com
- patch github.com
- web github.com
- web github.com