Vulnerability in cowboy (CVE-2026-8466)
Summary
Vulnerability in cowboy (CVE-2026-8466). Risk of unauthorized operations or information disclosure. Mitigation: upgrade to 2.15.0 or later.
Original description
The description as published by the source.
Summary
Allocation of Resources Without Limits or Throttling vulnerability in ninenines cowboy allows denial of service via unbounded buffer accumulation in multipart header parsing.
cowboy_req:read_part/3 in src/cowboy_req.erl accumulates incoming request bytes into a Buffer binary with no upper-bound check. When cow_multipart:parse_headers/2 returns more or {more, Buffer2}, the function reads up to Length bytes (default 64 KB) from the request body and recurses with the enlarged buffer. There is no equivalent of the byte_size(Acc) > Length guard present in the sibling function read_part_body/4. An unauthenticated attacker can send a multipart/form-data request whose body never yields a complete header section — for example, a body that never contains the advertised boundary delimiter, or one whose header lines never contain \r\n\r\n — and force the server process to accumulate memory linearly with the bytes the protocol layer is willing to deliver. A handful of concurrent such uploads is sufficient to exhaust BEAM memory.
This issue affects cowboy from 2.0.0 before 2.15.0.
Configurations
The application must expose an HTTP endpoint that calls cowboy_req:read_part/1,2 to process multipart/form-data request bodies. Deployments that do not handle multipart uploads are not affected.
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-2026-8466 has been found in cowboy.
Risk of unauthorized operations or information disclosure.
What to do: upgrade cowboy to 2.15.0 or later.
If unsure, ask your IT team or search "cowboy CVE-2026-8466" on the vendor's site.
CVE-2026-8466 (cowboy) — CWE-770
Patched: 2.15.0 — 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 cowboy.
Check the vendor advisory for the affected versions of cowboy.
Severity: ?. Risk of unauthorized operations or information disclosure.
Update to 2.15.0.
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 'cowboy' . 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 'cowboy' . | 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
cowboy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 cowboy to 2.15.0ステージング環境で 2.15.0 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。
-
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-2026-8466 erlang-cowboy Fixed in: 2.16.1+dfsg-1
- Ubuntu UBUNTU-CVE-2026-8466 erlang-cowboy
References
- advisory nvd.nist.gov
- package hex.pm
- package github.com
- patch github.com
- web cna.erlef.org
- web osv.dev
- web github.com