CVE-2024-49768

Waitress has request processing race condition in HTTP pipelining with invalid first request

Workarounds

Disable channel_request_lookahead, this is set to 0 by default disabling this feature. For this vulnerability this value is required to be changed from the default.

For more information

If you have any questions or comments about this advisory:

• Open an issue in https://github.com/Pylons/waitress/issues (if not sensitive or security related)
• email the Pylons Security mailing list: [email protected] (if security related)

Thanks

• m4yfly and urn1ce From TianGong Team of Legendsec at Qi'anxin Group.

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.

CVE-2024-49768 has a CVSS score of 9.1 (Critical). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (3.0.1); upgrading removes the vulnerable code path.

Kodem intelligence

Already deployed Kodem?

Waitress 3.0.1 fixes the race condition.

1. What is CVE-2024-49768? CVE-2024-49768 is a critical-severity security vulnerability in waitress (pip), affecting versions >= 2.0.0, < 3.0.1. It is fixed in 3.0.1.
2. How severe is CVE-2024-49768? CVE-2024-49768 has a CVSS score of 9.1 (Critical). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of waitress are affected by CVE-2024-49768? waitress (pip) versions >= 2.0.0, < 3.0.1 is affected.
4. Is there a fix for CVE-2024-49768? Yes. CVE-2024-49768 is fixed in 3.0.1. Upgrade to this version or later.
5. Is CVE-2024-49768 exploitable, and should I be worried? Whether CVE-2024-49768 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2024-49768 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2024-49768? Upgrade waitress to 3.0.1 or later.

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