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CVE-2026-42561 high CVSS 7.5

Vulnerability in python-multipart (CVE-2026-42561)

Summary

Vulnerability in python-multipart (CVE-2026-42561). Risk of unauthorized operations or information disclosure. Exploitable via MultipartParser. Mitigation: upgrade to 0.0.27 or later.

Original description

The description as published by the source.

Python-Multipart is a streaming multipart parser for Python. Prior to 0.0.27, python-multipart has a denial of service vulnerability in multipart part header parsing. When parsing multipart/form-data, MultipartParser previously had no limit on the number of part headers or the size of an individual part header. An attacker could send a request with either many repeated headers without terminating the header block or a single very large header value, causing excessive CPU work before request rejection or completion. This vulnerability is fixed in 0.0.27.

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-2026-42561 has been found in python-multipart.
Attackers can target a specific entry point like MultipartParser over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 7.5/10.
What to do: upgrade python-multipart to 0.0.27 or later.
If unsure, ask your IT team or search "python-multipart CVE-2026-42561" on the vendor's site.

CVE-2026-42561 (python-multipart) — CWE-770 / CVSS v3 7.5
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: MultipartParser / HEADER_FIELD_START / HEADER_FIELD / HEADER_VALUE_START
Patched: 0.0.27 — apply immediately
Workaround: reduce exposure by enforcing request body size limits at the server, proxy, or framework layer.
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.

❓ What is the problem

A vulnerability (CWE-770) exists in python-multipart. Attackers reach the vulnerable code path via MultipartParser without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of python-multipart. Attack surface: MultipartParser / HEADER_FIELD_START / HEADER_FIELD / HEADER_VALUE_START.

🔥 Severity

Severity: High (CVSS 7.5/10). Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to 0.0.27.

🛡️ Workaround

Workaround: reduce exposure by enforcing request body size limits at the server, proxy, or framework layer.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'python-multipart' . 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

  1. 1
    Identify exposure identify 
    grep -r 'python-multipart' . | 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 python-multipart を grep し、稼働しているサービス・バージョンを把握する。

  2. 2
    Apply temporary workaround mitigate 
    reduce exposure by enforcing request body size limits at the server, proxy, or framework layer.

    パッチが適用されるまでの応急処置として、reduce exposure by enforcing request body size limits at the server, proxy, or framework layer. を実施。回避策の副作用 (機能低下) を確認した上で。

  3. 3
    Apply patch patch 
    Upgrade python-multipart to 0.0.27

    ステージング環境で 0.0.27 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。

  4. 4
    Post-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

pip python-multipart
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0.0.27"}]}]
PyPI python-multipart
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0.0.27"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

References

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