Vulnerability in multer (CVE-2026-77063)
Summary
Vulnerability in multer (CVE-2026-77063). Risk of unauthorized operations or information disclosure. Exploitable via multer. Mitigation: upgrade to 2.3.0 or later.
Original description
The description as published by the source.
Impact
When multer is configured with an asynchronous fileFilter, the limits.fileSize limit can be bypassed. The 'limit' event is registered inside the async fileFilter callback, so if a file exceeds limits.fileSize before that callback runs, the event is missed and the oversized upload is accepted instead of being rejected with a LIMIT_FILE_SIZE error. Applications that rely on limits.fileSize to reject oversized uploads are affected on all upload methods (.single(), .array(), .fields(), .any()). Uploads using a synchronous fileFilter are not affected.
Patches
Users should upgrade to 2.3.0.
Workarounds
Use a synchronous fileFilter, or validate the uploaded file size after the upload completes.
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-2026-77063 has been found in multer.
Attackers can target a specific entry point like multer over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 3.7/10.
What to do: upgrade multer to 2.3.0 or later.
If unsure, ask your IT team or search "multer CVE-2026-77063" on the vendor's site.
CVE-2026-77063 (multer) — CWE-362 / CVSS v3 3.7
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: multer / fileFilter / limits.fileSize / LIMIT_FILE_SIZE
Patched: 2.3.0 — apply immediately
Workaround: Use a synchronous fileFilter, or validate the uploaded file size after the upload completes.
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-362) exists in multer. Attackers reach the vulnerable code path via multer without authentication.
Check the vendor advisory for the affected versions of multer. Attack surface: multer / fileFilter / limits.fileSize / LIMIT_FILE_SIZE.
Severity: Low (CVSS 3.7/10). Risk of unauthorized operations or information disclosure.
Update to 2.3.0.
Workaround: Use a synchronous fileFilter, or validate the uploaded file size after the upload completes.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'multer' . 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 'multer' . | 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
multerを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply temporary workaround mitigate
Use a synchronous `fileFilter`, or validate the uploaded file size after the upload completes.パッチが適用されるまでの応急処置として、Use a synchronous
fileFilter, or validate the uploaded file size after the upload completes. を実施。回避策の副作用 (機能低下) を確認した上で。 -
3Apply patch patch
Upgrade multer to 2.3.0ステージング環境で 2.3.0 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。
-
4Post-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 nvd.nist.gov
- package github.com
- web cna.openjsf.org
- web github.com
- web github.com
- web github.com
- web github.com