Vulnerability in starlette (CVE-2026-54283)
Summary
Vulnerability in starlette (CVE-2026-54283). Risk of unauthorized operations or information disclosure. Exploitable via max_fields. Mitigation: upgrade to 1.3.1 or later.
Original description
The description as published by the source.
Summary
request.form() accepts max_fields and max_part_size to bound resource consumption while parsing form data. These limits are enforced for multipart/form-data, but silently ignored for application/x-www-form-urlencoded. An unauthenticated attacker can therefore send a urlencoded body with an arbitrarily large number of fields or an arbitrarily large field, even when the application configured limits it believed would apply.
Details
request.form() dispatches to a different parser depending on the Content-Type. For multipart/form-data the max_files, max_fields, and max_part_size limits are forwarded to the parser, but for application/x-www-form-urlencoded the parser is constructed without them. It has no max_fields or max_part_size parameter to receive them, and it appends every field with no count check and accumulates each field's name and value with no size check. The configured limits are therefore both unreachable and unenforced for url-encoded bodies.
Because the url-encoded parser does its work synchronously between stream reads, the two attack shapes have different effects:
- Field count drives CPU and event-loop blocking. A body of ~1,000,000 fields (a sub-10MB payload such as
f0=v&f1=v&...) blocks the worker's event loop for several seconds while parsing, during which the worker serves no other request. - Field size drives memory. A single large field value (e.g. a 50MB value) is buffered in full to build the `For…
Source: GitHub Security Advisories (Global) 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-2026-54283 has been found in starlette.
Attackers can target a specific entry point like max_fields over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 7.5/10.
What to do: upgrade starlette to 1.3.1 or later.
If unsure, ask your IT team or search "starlette CVE-2026-54283" on the vendor's site.
CVE-2026-54283 (starlette) — CWE-770 / CVSS v3 7.5
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: max_fields / max_part_size / max_files / FormData
Patched: 1.3.1 — 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-770) exists in starlette. Attackers reach the vulnerable code path via max_fields without authentication.
Check the vendor advisory for the affected versions of starlette. Attack surface: max_fields / max_part_size / max_files / FormData.
Severity: High (CVSS 7.5/10). Risk of unauthorized operations or information disclosure.
Update to 1.3.1.
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 'starlette' . 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
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1Identify exposure identify
grep -r 'starlette' . | 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
starlette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 starlette to 1.3.1ステージング環境で 1.3.1 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
Fix status by distribution
Fixed packages published by each distribution for this CVE
- Debian DEBIAN-CVE-2026-54283 starlette Fixed in: 0.26.1-1+deb12u2
- Ubuntu UBUNTU-CVE-2026-54283 starlette
References
- package github.com
- web github.com
- web github.com