Vulnerability in waitress (CVE-2019-16786)

Summary

Vulnerability in waitress (CVE-2019-16786). Confidential information can be exposed externally. Exploitable via chunked. Mitigation: upgrade to 1.4.0 or later.

Original description

The description as published by the source.

Impact

Waitress would parse the Transfer-Encoding header and only look for a single string value, if that value was not chunked it would fall through and use the Content-Length header instead.

According to the HTTP standard Transfer-Encoding should be a comma separated list, with the inner-most encoding first, followed by any further transfer codings, ending with chunked.

Requests sent with:

Transfer-Encoding: gzip, chunked

Would incorrectly get ignored, and the request would use a Content-Length header instead to determine the body size of the HTTP message.

This could allow for Waitress to treat a single request as multiple requests in the case of HTTP pipelining.

Patches

This issue is fixed in Waitress 1.4.0. This brings a range of changes to harden Waitress against potential HTTP request confusions, and may change the behaviour of Waitress behind non-conformist proxies.

Waitress will now return a 501 Not Implemented error if the Transfer-Encoding is not chunked or contains multiple elements. Waitress does not support any transfer codings such as gzip or deflate.

The Pylons Project recommends upgrading as soon as possible, while validating that the changes in Waitress don't cause any changes in behavior.

Workarounds

Various reverse proxies may have protections against sending potentially bad HTTP requests to the backend, and or hardening against potential issues like this. If the reverse proxy doesn't use HTTP/1.1…

Source: OSV.dev (Open Source Vulnerabilities) NVD GitHub Advisory OSV

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-2019-16786 has been found in waitress.
Attackers can target a specific entry point like chunked over the network to misuse the product.
Confidential information can be exposed externally.
What to do: upgrade waitress to 1.4.0 or later.
If unsure, ask your IT team or search "waitress CVE-2019-16786" on the vendor's site.

CVE-2019-16786 (waitress) — CWE-444
Attack vector: remote (network-reachable) / no user interaction
Attack surface: chunked / gzip / deflate
Patched: 1.4.0 — apply immediately
Workaround: Various reverse proxies may have protections against sending potentially bad HTTP requests to the backend, and or hardening against potential issues like this.
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-444) exists in waitress. Attackers reach the vulnerable code path via chunked.

📍 Affected scope

Check the vendor advisory for the affected versions of waitress. Attack surface: chunked / gzip / deflate.

🔥 Severity

Severity: ?. Confidential information can be exposed externally.

🔧 How to fix

Update to 1.4.0.

🛡️ Workaround

Workaround: Various reverse proxies may have protections against sending potentially bad HTTP requests to the backend, and or hardening against potential issues like this.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'waitress' . 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
Identify exposure identify
```
grep -r 'waitress' . | 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 waitress を grep し、稼働しているサービス・バージョンを把握する。
2
Apply temporary workaround mitigate
```
Various reverse proxies may have protections against sending potentially bad HTTP requests to the backend, and or hardening against potential issues like this.
```
パッチが適用されるまでの応急処置として、Various reverse proxies may have protections against sending potentially bad HTTP requests to the backend, and or hardening against potential issues like this. を実施。回避策の副作用 (機能低下) を確認した上で。
3
Apply patch patch
```
Upgrade waitress to 1.4.0
```
ステージング環境で 1.4.0 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。
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

PyPI waitress

[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.4.0"}]}]