CVE-2026-110354

HAProxy 3 before 3.4.6 allows a remote unauthenticated attacker to cause a denial of service (persistent worker-thread CPU exhaustion) via an HTTP/1.1 chunked request. Although the H1 multiplexer drains the request before closing the stream, the parser repeatedly re-processes the same bytes without making progress. The affected thread stays busy at 100% CPU after timeouts expire and after the client disconnects, and repeated requests can consume all worker threads until the process is restarted.

CVE-2026-110354 is fixed in 2 products on 1 platform, first by DEBIAN-CVE-2026-110354, released October 27, 2026. It is not reported as exploited. Patch Radar priority: High.

High

CVSS

7.5

Important

Exploitation

None reported

No vendor assessment

CISA KEV

Not listed

Not in the Known Exploited Vulnerabilities catalog

EPSS

0.0081

57th percentile

HAProxy 3 before 3.4.6 allows a remote unauthenticated attacker to cause a denial of service (persistent worker-thread CPU exhaustion) via an HTTP/1.1 chunked request. Although the H1 multiplexer drains the request before closing the stream, the parser repeatedly re-processes the same bytes without making progress. The affected thread stays busy at 100% CPU after timeouts expire and after the client disconnects, and repeated requests can consume all worker threads until the process is restarted.

Where it's fixed

Product	Fixed in	Fix	Released
Linux
haproxy · Debian 12.15 (bookworm)	2.6.12-1+deb12u4	DEBIAN-CVE-2026-110354	Oct 27, 2026
haproxy · Debian 13.5 (trixie)	3.0.11-1+deb13u4	DEBIAN-CVE-2026-110354	Oct 27, 2026
haproxy · Debian 14	3.2.26-1	DEBIAN-CVE-2026-110354	Oct 27, 2026
haproxy · Ubuntu 22.04.1 LTS (jammy)	2.4.30-0ubuntu0.22.04.3	haproxy 2.4.30-0ubuntu0.22.04.3	Nov 4, 2026
haproxy · Ubuntu 24.04.5 LTS (noble)	2.8.30-0ubuntu0.24.04.2	haproxy 2.8.30-0ubuntu0.24.04.2	Nov 4, 2026
haproxy · Ubuntu 26.04.1 LTS (resolute)	3.2.25-0ubuntu0.26.04.2	haproxy 3.2.25-0ubuntu0.26.04.2	Nov 7, 2026
vim-haproxy · Ubuntu 22.04.1 LTS (jammy)	2.4.30-0ubuntu0.22.04.3	vim-haproxy 2.4.30-0ubuntu0.22.04.3	Nov 4, 2026
vim-haproxy · Ubuntu 24.04.5 LTS (noble)	2.8.30-0ubuntu0.24.04.2	vim-haproxy 2.8.30-0ubuntu0.24.04.2	Nov 4, 2026
vim-haproxy · Ubuntu 26.04.1 LTS (resolute)	3.2.25-0ubuntu0.26.04.2	vim-haproxy 3.2.25-0ubuntu0.26.04.2	Nov 7, 2026

Details

Published
October 21, 2026
Weakness
Loop with Unreachable Exit Condition ('Infinite Loop')
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Vendor advisory
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-110354

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