critical CVSS 9.1

CVE-2024-49768·Python vulnerability

Waitress is a Web Server Gateway Interface server for Python 2 and 3. A remote client may send a request that is exactly recv_bytes (defaults to 8192) long, followed by a secondary request using HTTP pipelining. When request lookahead is disabled (default) we won't read any more requests, and when the first request fails due to a parsing error, we simply close the connection. However when request lookahead is enabled, it is possible to process and receive the first request, start sending the error message back to the client while we read the next request and queue it. This will allow the secondary request to be serviced by the worker thread while the connection should be closed. Waitress 3.0.1 fixes the race condition. As a workaround, disable channel_request_lookahead, this is set to 0 by default disabling this feature.

Severity
critical
Software
Python
Fixed in
3.0.1
Published
2024-10-29

Affected versions

From: 2.0.0

Until: 3.0.1

Fixed in: 3.0.1

How to fix this CVE

Update Waitress to version 3.0.1 or later to patch a race condition in HTTP request handling that can lead to unauthorized request processing. Organizations running Waitress versions 2.0.0 through 3.0.0 should prioritize this update immediately. As a temporary workaround, ensure channel_request_lookahead is disabled (the default setting) to prevent the vulnerable code path from being triggered.

sudo dnf update python3-waitress

Defensia detects this vulnerability

What an exploitation attempt looks like

Sample log line indicative of exploitation attempts:

HTTP/1.1 request exactly 8192 bytes in length followed immediately by a secondary request using HTTP pipelining, with the first request triggering a parsing error response while the second request is queued for processing

WAF mitigation (if patching is not yet possible)

Add this rule to your WAF to block exploitation attempts while you schedule the patch. 

Configure WAF rules to disable HTTP request pipelining or implement strict request size limits that prevent requests from reaching exactly the recv_bytes threshold (default 8192). Monitor for multiple requests within the same TCP connection arriving in close succession and rate-limit or block such patterns.

How to check if you are affected

  1. Step 1: Check the installed Waitress version by running: python3 -c "import waitress; print(waitress.__version__)"
  2. Step 2: If using Waitress as a WSGI server, verify the channel_request_lookahead configuration in your Waitress setup by checking for it in your application's server configuration file or environment variables
  3. Step 3: Search application logs for multiple requests arriving in rapid succession or HTTP/1.1 pipelined requests followed by parsing errors, which may indicate exploitation attempts
  4. Step 4: After patching to version 3.0.1+, re-run the version check command to confirm: python3 -c "import waitress; print(waitress.__version__)" should show 3.0.1 or higher

FAQ

What is CVE-2024-49768?

CVE-2024-49768 is a race condition vulnerability in Waitress (Python WSGI server) that occurs when HTTP request lookahead is enabled, allowing a secondary pipelined HTTP request to be processed even after the connection should have been closed due to a parsing error in the first request.

Is CVE-2024-49768 being actively exploited?

No, CVE-2024-49768 is not currently listed on the CISA Known Exploited Vulnerabilities (KEV) catalog, and no public exploits are available.

What versions of Python are affected by CVE-2024-49768?

Waitress versions 2.0.0 through 3.0.0 are affected. The vulnerability is patched in Waitress 3.0.1 and later. This affects any Python application using Waitress as its WSGI server.

How do I check if my server is vulnerable to CVE-2024-49768?

Run `python3 -c "import waitress; print(waitress.__version__)"` to check the installed version. If it is 2.0.0 or higher but lower than 3.0.1, your server is vulnerable. Also verify that channel_request_lookahead is not explicitly enabled to true in your configuration.

Does Defensia detect CVE-2024-49768?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Waitress is installed on a monitored server, CVE-2024-49768 will appear in your dashboard with remediation steps.

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References

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