Vulnerability in MyBB (CVE-2026-45118)
Summary
Vulnerability in MyBB (CVE-2026-45118). Confidential information can be exposed externally. Exploitable via Referer header.
Original description
The description as published by the source.
MyBB is free and open source forum software. Prior to 1.8.40, the Contact module does not validate a redirect URL or protocol correctly, resulting in an open redirect and reflected JavaScript code injection. contact.php accepts the redirect target from the from HTTP parameter in $mybb->input['from'] or the Referer HTTP header in $_SERVER['HTTP_REFERER'] and passes it to redirect() without sufficient verification. A javascript: URI becomes the target of the Click here if you don't want to wait any longer link because $force_redirect is true, allowing script execution when a victim selects the link. This issue is fixed in version 1.8.40.
Source: NIST National Vulnerability Database NVD
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-2026-45118 has been found in MyBB.
Attackers can target a specific entry point like Referer header over the network to misuse the product.
Confidential information can be exposed externally. CVSS score: 9.3/10.
What to do: apply the vendor's official patched release.
If unsure, ask your IT team or search "MyBB CVE-2026-45118" on the vendor's site.
CVE-2026-45118 (MyBB) — CWE-83 / CVSS v3 9.3
Attack vector: remote (network-reachable) / unauthenticated
Attack surface: Referer header
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-83) exists in MyBB. Attackers reach the vulnerable code path via Referer header without authentication.
Check the vendor advisory for the affected versions of MyBB. Attack surface: Referer header.
Severity: Critical (CVSS 9.3/10). Confidential information can be exposed externally.
Update to the patched release per vendor advisory.
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 'MyBB' . 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 'MyBB' . | 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
MyBBを grep し、稼働しているサービス・バージョンを把握する。 -
2Post-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。