CVE-2026-33555

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.

Published: 2026-04-13 Last update: 2026-04-22 Assigner: [email protected] Source: [email protected]
NVD Status：Awaiting Analysis，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2026-33555 is rated Low Risk (16.3/100): CVSS Medium severity, with low exploitation likelihood (EPSS 0.01%). Low composite risk—no urgent action required; patch on your normal maintenance cycle and revisit priority if CVSS or EPSS increases.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2026-33555

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-04-14 — 0.01% —

Full EPSS history (1 record total)

Common vulnerability scoring system (CVSS) metrics for CVE-2026-33555

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
4.0 3.1 MEDIUM
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:L/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:H)
Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:C)
Breaking this can reach past the original component and bite other resources—bigger blast radius.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:L)
Attackers could change some data, but it’s limited—not everything goes.
Availability (A:N)
Service keeps running; no real outage angle.
 2.2 1.4 [email protected]

Weakness enumeration for CVE-2026-33555

GitHub Security Advisory for CVE-2026-33555

GHSA-5mp8-rq5m-pj7m · Severity: medium — An issue was discovered in HAProxy before 3.3.6. The HTTP/3 parser does not check that the...

OS Trackers for CVE-2026-33555

vendor priority summary link
debian unimportant CVE-2026-33555 unimportant priority: Debian including 1 source packages (haproxy), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 4, open 1. https://security-tracker.debian.org/tracker/CVE-2026-33555
redhat medium — https://access.redhat.com/security/cve/CVE-2026-33555
suse medium CVE-2026-33555 severity moderate: SUSE including 1 source package names (haproxy), 7 product×package rows across 7 product lines (SUSE Linux Enterprise High Availability Extension 12 SP5, SUSE Linux Enterprise High Availability Extension 15 SP4, … (7 product lines)): Known Not Affected 7. https://www.suse.com/security/cve/CVE-2026-33555/
ubuntu medium CVE-2026-33555 medium priority: Ubuntu including 1 source packages (haproxy), 8 status rows across 8 suites (bionic, focal, jammy, noble, questing, resolute, upstream, xenial): not-affected 4, released 4. https://ubuntu.com/security/CVE-2026-33555

Affected software / configurations for CVE-2026-33555

Vendor Product Version Raw CPE
No affected products in dataset.

References for CVE-2026-33555

cvelogic Threat Intelligence