Vulnerability in exceljs-hardened (CVE-2026-78207)
Summary
Vulnerability in exceljs-hardened (CVE-2026-78207). Confidential information can be exposed externally.
Original description
The description as published by the source.
exceljs-hardened before 5.0.0 contains a prototype pollution vulnerability in the deepMerge helper that fails to reject proto, constructor, or prototype keys when merging note objects. Attackers can assign parsed JSON with a malicious proto property to cell notes, modifying Object.prototype and affecting all plain objects created in the process.
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-2026-78207 has been found in exceljs-hardened.
Confidential information can be exposed externally. CVSS score: 9.4/10.
What to do: apply the vendor's official patched release.
If unsure, ask your IT team or search "exceljs-hardened CVE-2026-78207" on the vendor's site.
CVE-2026-78207 (exceljs-hardened) — CWE-1321 / CVSS v3 9.4
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
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-1321) exists in exceljs-hardened.
Check the vendor advisory for the affected versions of exceljs-hardened.
Severity: Critical (CVSS 9.4/10). 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 'exceljs-hardened' . 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 'exceljs-hardened' . | 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
exceljs-hardened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。