Disclosure summary
An issue was discovered in HAProxy before 3.3.6. The HTTP/3 parser does not check that the received body length matches a previously announced content-length when the stream is closed via a frame with an empty payload. This can cause desynchronization issues with the backend server and could be used for request smuggling. The earliest affected version is 2.6.
Source-reported weakness categories
CWE-130
Source-specific records & product guidance
Sources retain their own attribution and scoring. Follow the original record to confirm affected versions, fixed releases, and configuration conditions.
Microsoft Security Updates (CVRF) · 2026-Apr
Open original source · Updated Apr 29, 2026
An issue was discovered in HAProxy before 3.3.6. The HTTP/3 parser does not check that the received body length matches a previously announced content-length when the stream is closed via a frame with an empty payload. This can cause desynchronization issues with the backend server and could be used for request smuggling. The earliest affected version is 2.6.
Maximum of vendor-reported product scores; products and fixed builds are associations, not a universal affected-version statement.
Microsoft maximum product score: 4
| Vendor | Product / association | Version / bounds |
|---|---|---|
| Microsoft update guide | azl3 haproxy 2.9.11-4 on Azure Linux 3.0 | (MSRC status code 3) |
| Microsoft update guide | azl3 haproxy 2.9.11-5 on Azure Linux 3.0 | (MSRC status code 3) |
Vendor remediation references
- CBL-Mariner Releases · build 2.9.11-5 · product IDs 20734-17084, 21285-17084
- Vendor guidance · product IDs 20734-17084, 21285-17084
Original records & references
- NIST NVD record
- CVE Program record
- msrc.microsoft.com — Vendor advisory
PUBLISHED 2026-04-14T21:01:51-04:00
MODIFIED 2026-04-29T10:57:49-04:00
INGESTED 2026-10-08T12:45:03-04:00