Integer underflow in HAProxy - CVE-2026-26081

Vulnerability identifier: #VU122782

CSH Severity: Medium

CVSS v4: 8.7 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]

CVE-ID: CVE-2026-26081

CWE-ID: CWE-191

Exploitation vector: Remote access

Exploit availability: No public exploit available

The vulnerability allows a remote attacker to perform a denial of service attack.

The vulnerability exists due to integer underflow when handling QUIC packets. A remote attacker can send a specially crafted request to the server, trigger an integer underflow and perform a denial of service attack.

HAProxy
Debian Linux
openEuler
Ubuntu
haproxy (Debian package)
haproxy
haproxy-debuginfo
haproxy-debugsource
haproxy-help
haproxy (Ubuntu package)

Install updates from vendor's website.

HAProxy - addressed in versions 3.0.16, 3.1.14, 3.2.12, 3.3.3
haproxy (Debian package) - update to 3.0.11-1+deb13u2
haproxy - update to 3.0.11-4
haproxy-debuginfo - update to 3.0.11-4
haproxy-debugsource - update to 3.0.11-4
haproxy-help - update to 3.0.11-4
haproxy (Ubuntu package) - update to 3.0.12-0ubuntu0.25.10.3

• https://www.mail-archive.com/haproxy@formilux.org/msg46589.html
• https://www.haproxy.com/blog/cves-2026-quic-denial-of-service
• https://git.haproxy.org/?p=haproxy-3.0.git;a=commit;h=a05eade0f07483e6b6d0b61b1749e9093647e802
• https://git.haproxy.org/?p=haproxy-3.2.git;a=commit;h=4765277f4f915baac2d57db63538ff0a59966deb

• Two denial of service vulnerabilities in haproxy QUIC parsing
• Debian update for haproxy
• Ubuntu update for haproxy
• openEuler 24.03 LTS SP4 update for haproxy
• openEuler 24.03 LTS SP3 update for haproxy