CVE-2024-49768: Waitress has request processing race condition in HTTP pipelining with invalid first request

Should you act?

Critical and remotely reachable

No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
• EPSS 0.5%, percentile 41: FIRST’s model estimates a 0.5% chance of exploitation activity in the next 30 days, higher than 41% of all scored CVEs (low). EPSS is a probability, not a verdict.
• Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
• Only applies if your dependency tree includes waitress (PyPI) >= 2.0.0, < 3.0.1, fixed in 3.0.1. Check your lockfile, including transitive dependencies.

What it is

Waitress is a Web Server Gateway Interface server for Python 2 and 3. A remote client may send a request that is exactly recvbytes (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 channelrequestlookahead, this is set to 0 by default disabling this feature.

From the GitHub advisory

Impact

A remote client may send a request that is exactly recvbytes (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.

Patches

Weakness type: CWE-367, CWE-444.

Product: waitress (PyPI) · Assigned by: GitHub_M · Published: 2024-10-29

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Attack requirements: none
• Privileges required: none (no login)
• User interaction: none

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation none, automatable yes, technical impact total.
• FIRST EPSS (model of 2026-10-21): 0.49% probability of exploitation activity in the next 30 days; percentile 41.

Timeline

• 2024-10-29 — CVE record last updated
• 2024-10-29 — CVE record published by GitHub_M
• 2024-10-29 — GitHub-reviewed advisory GHSA-9298-4cf8-g4wj published (critical)

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-9298-4cf8-g4wj github.com
2. CVE.org record CVE-2024-49768 cve.org
3. NVD entry CVE-2024-49768 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. github.com github.com
3. github.com github.com

Critical PyPI advisories · Today’s Security Digest