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NVD / CVE Program· CNA mitre

CVE-2026-33555: An issue was discovered in HAProxy before 3.3.6.

Noroxi assessment

Priority: Monitor (action score 23/100)

  • Public proof-of-concept code exists (GitHub); there is no record of exploitation in the wild.
  • Probability of exploitation in the next 30 days: 0.30% (FIRST EPSS).
  • Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
  • Fixed version: azl3 haproxy 2.9.11-4 on Azure Linux 3.0 2.9.11-5; azl3 haproxy 2.9.11-5 on Azure Linux 3.0 2.9.11-5.

Low priority for now. Upgrade to azl3 haproxy 2.9.11-4 on Azure Linux 3.0 2.9.11-5; azl3 haproxy 2.9.11-5 on Azure Linux 3.0 2.9.11-5 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

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.

MediumCVSS 5.8 · v3.1—Proof of concept Fix available
Published
Apr 13, 2026
Updated
Oct 18, 2026
EPSS
0.3% · 23th percentile

Report tools

JSON

Action score

23

Monitor

Low priority for now.

CVSS
23 / 40 · 5.8 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.3%

CISA SSVC decision

Exploitation
proof of concept
Automatable
no
Technical impact
partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD
5.8
CNA · mitre
4.0
1.8 point gap

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:L/A:N

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

  • Not in KEV: no record of exploitation in the wild
  • Proof of concept exists, no weaponized module
  • A fix has been released

If any of these changes, we'll tell you in the daily email digest.

Follow CVE-2026-33555

When you'll hear from us

  • when it enters CISA KEV
  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
haproxyhaproxy

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • haproxy haproxy2.6.0 and later · before 3.3.6

Versions reported by the vendor

Affected version ranges reported by the assigning authority (mitre). Independent of NVD's CPE analysis and usually ahead of it.

  • HAProxy HAProxy

    • 2.6 and later · before 3.3.6affected

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Debian:12haproxybefore 2.6.12-1+deb12u42.6.12-1+deb12u4
Debian:13haproxybefore 3.0.11-1+deb13u33.0.11-1+deb13u3
Debian:14haproxybefore 3.2.15-13.2.15-1
openSUSE:Leap 16.0haproxybefore 3.2.15+git64.0fc44b458-160000.2.13.2.15+git64.0fc44b458-160000.2.1
openSUSE:Tumbleweedhaproxybefore 3.3.6+git91.af5637e93-1.13.3.6+git91.af5637e93-1.1
Red Hat:hummingbird:1haproxybefore 0:3.0.19-1.1.hum10:3.0.19-1.1.hum1
SUSE:Linux Enterprise High Availability Extension 15 SP6haproxybefore 2.8.11+git0.01c1056a4-150600.3.12.12.8.11+git0.01c1056a4-150600.3.12.1
SUSE:Linux Micro 6.2haproxybefore 3.2.15+git64.0fc44b458-160000.2.13.2.15+git64.0fc44b458-160000.2.1

Same product

haproxy: all records

Other highest-scoring records for the same primary product.

  • CVE-2020-11100In hpack_dht_insert in hpack-tbl.c in the HPACK decoder in HAProxy 1.8 through 2.x before 2.1.4, a remote attacker can write arbitrary bytes
    53Plan
  • CVE-2019-14241HAProxy through 2.0.2 allows attackers to cause a denial of service (ha_panic) via vectors related to htx_manage_client_side_cookies in prot
    51Plan
  • CVE-2021-40346An integer overflow exists in HAProxy 2.0 through 2.5 in htx_add_header that can be exploited to perform an HTTP request smuggling attack, a
    48Plan

Published before and after this one in the same product

  • ← EarlierCVE-2024-45506Sep 4, 2024 · HAProxy 2.9.x before 2.9.10, 3.0.x before 3.0.4, and 3.1.x through 3.1-dev6 allows a remote denial of service for HTTP/2 zero-copy forwardin
    30Monitor
  • ← EarlierCVE-2025-32464Apr 8, 2025 · HAProxy 2.2 through 3.1.6, in certain uncommon configurations, has a sample_conv_regsub heap-based buffer overflow because of mishandling of
    27Monitor
  • Later →CVE-2026-55203Jun 18, 2026 · HAProxy - Integer Overflow in FCGI Demux Record Length Field
    36Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
azl3 haproxy 2.9.11-4 on Azure Linux 3.02.9.11-5 · CBL-Mariner ReleasesMicrosoft (MSRC)
azl3 haproxy 2.9.11-5 on Azure Linux 3.02.9.11-5 · CBL-Mariner ReleasesMicrosoft (MSRC)
debian:haproxy2.6.12-1+deb12u4 · Debian:12Package registry (OSV)
debian:haproxy3.0.11-1+deb13u3 · Debian:13Package registry (OSV)
opensuse:haproxy3.3.6+git91.af5637e93-1.1 · openSUSE:TumbleweedPackage registry (OSV)
red hat:haproxy0:3.0.19-1.1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
suse:haproxy2.8.11+git0.01c1056a4-150600.3.12.1 · SUSE:Linux Enterprise High Availability Extension 15 SP6Package registry (OSV)

Exploit status

Proof of concept available

A public proof of concept or detection signature exists. Exploit knowledge is out there; don't delay patching.

Evidence

  • Proof-of-concept repository on GitHub ×1

Noroxi does not host or link to exploit code. Metasploit module names and Nuclei template ids are shown (names, not code); Exploit-DB entries and PoC repositories are given as counts only.

Public exploit evidence
SourceKindDate
Proof-of-concept repository on GitHubstars:22026-04-16

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

  1. Published
  2. First PoC+2 d
  3. TodayNov 6, 2026+207 d

No history yet (it accumulates with the daily EPSS job).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

  • CVE-2026-90678153 days apartAn issue was discovered in HAProxy 3.3.0 through 3.4.4 and in 3.5-dev1 through 3.5-dev5.
    30Monitor
  • CVE-2026-2608198 days apartHAProxy Community Edition 3.0 through 3.3 before 3.3.3 lacks a length check for the NEW_TOKEN format.
    19Monitor

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • No account or password is required.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
none
Integrity
low · data or configuration can be modified
Availability
none

Impact can extend beyond the vulnerable component (scope changes).

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Changed
Confidentiality impact
None
Integrity impact
Low
Availability impact
None

Weakness class (CWE)

CWE-130 · Improper Handling of Length Parameter Inconsistency

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N

nvd-primary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

ATT&CK techniques

—

Change log

  1. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

Show all references (4 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records