CVE-2026-55204: HAProxy - NULL Pointer Dereference in hpack_dht_insert Function
Noroxi assessment
Priority: Monitor (action score 34/100)
- The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
- Probability of exploitation in the next 30 days: 0.48% (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.
- According to CISA the attack is automatable: targets can be found by mass scanning.
- Fixed version: azl3 haproxy 2.9.11-6 on Azure Linux 3.0 2.9.11-7; azl3 haproxy 2.9.11-7 on Azure Linux 3.0 2.9.11-7.
Low priority for now. Upgrade to azl3 haproxy 2.9.11-6 on Azure Linux 3.0 2.9.11-7; azl3 haproxy 2.9.11-7 on Azure Linux 3.0 2.9.11-7 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
HAProxy through 3.4.0, fixed in commit 9a6d1fe, contains a null pointer dereference vulnerability in hpack_dht_insert() within src/hpack-tbl.c that fails to validate the return value of hpack_dht_defrag() when the memory pool is exhausted. An attacker can trigger HPACK dynamic table insertions under memory pressure to dereference a NULL pointer and crash HAProxy worker processes, causing denial of service.
- BDU:2026-16139
- ALSA-2026:55679
- ALSA-2026:55772
- ALSA-2026:55859
- openSUSE-SU-2026:11090-1
- openSUSE-SU-2026:21245-1
- RHSA-2026:35453
- RHSA-2026:55679
- RHSA-2026:55772
- RHSA-2026:55800
- RHSA-2026:55801
- RHSA-2026:55802
- RHSA-2026:55803
- RHSA-2026:55859
- RHSA-2026:55860
- RHSA-2026:55861
- RHSA-2026:55862
- RLSA-2026:55679
- RLSA-2026:55772
- RLSA-2026:55859
- Published
- Jun 18, 2026
- Updated
- Oct 26, 2026
- EPSS
- 0.4% · 41th percentile
- CWE
- CWE-476
Report tools
Action score
34
Monitor
Low priority for now.
- CVSS
- 34 / 40 · 8.7 / 10
- CISA KEV
- 0 / 30 · Not listed
- EPSS
- 0 / 30 · 0.4%
CISA SSVC decision
- Exploitation
- none
- Automatable
- yes
- Technical impact
- partial
Vulnrichment: CISA's decision-tree inputs.
CNA vs NVD score
- NVD
- —
- CNA · VulnCheck
- 8.7
- NVD has not scored this yet; the score shown is the CNA’s.
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
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
- No public exploit code on record
- A fix has been released
If any of these changes, we'll tell you in the daily email digest.
Running WordPress? Scan your site free with WP Lens
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.
We use this product, ask for helpAffected 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.
| Vendor | Product | CPE |
|---|---|---|
| haproxy | haproxy | cpe:2.3:a:haproxy:haproxy |
Affected versions
NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.
- haproxy haproxybefore 2.4.36
- haproxy haproxy2.5 and later · before 2.6.30
- haproxy haproxy2.7 and later · before 2.8.25
- haproxy haproxy2.9 and later · before 3.0.24
- haproxy haproxy3.1 and later · before 3.2.20
- haproxy haproxy3.3 and later · before 3.4.1
Versions reported by the vendor
Affected version ranges reported by the assigning authority (VulnCheck). Independent of NVD's CPE analysis and usually ahead of it.
haproxy haproxy
- 9a6d1fe3f00d86ab4ea6ea6ea0a5d48fc058a513not affected
- up to and including 3.4.0affected · semver
Package-level exposure
OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.
| Ecosystem | Package | Affected range | Fix |
|---|---|---|---|
| AlmaLinux:10 | haproxy | before 3.0.5-6.el10_2.2 | 3.0.5-6.el10_2.2 |
| AlmaLinux:8 | haproxy | before 1.8.27-5.el8_10.2 | 1.8.27-5.el8_10.2 |
| AlmaLinux:9 | haproxy | before 2.8.14-3.el9_8.2 | 2.8.14-3.el9_8.2 |
| Debian:12 | haproxy | from 0 | — |
| Debian:14 | haproxy | before 3.2.20-1 | 3.2.20-1 |
| openSUSE:Leap 16.0 | haproxy | before 3.2.21+git0.dbe43be37-160000.1.1 | 3.2.21+git0.dbe43be37-160000.1.1 |
| openSUSE:Tumbleweed | haproxy | before 3.4.0+git31.fc300e9f2-1.1 | 3.4.0+git31.fc300e9f2-1.1 |
| Red Hat:enterprise_linux_eus:10.0 | haproxy | before 0:3.0.5-4.el10_0.3 | 0:3.0.5-4.el10_0.3 |
| Red Hat:enterprise_linux_eus:10.0 | haproxy-debuginfo | before 0:3.0.5-4.el10_0.3 | 0:3.0.5-4.el10_0.3 |
| Red Hat:enterprise_linux_eus:10.0 | haproxy-debugsource | before 0:3.0.5-4.el10_0.3 | 0:3.0.5-4.el10_0.3 |
| Red Hat:enterprise_linux:10.2 | haproxy | before 0:3.0.5-6.el10_2.2 | 0:3.0.5-6.el10_2.2 |
| Red Hat:enterprise_linux:10.2 | haproxy-debuginfo | before 0:3.0.5-6.el10_2.2 | 0:3.0.5-6.el10_2.2 |
| Red Hat:enterprise_linux:10.2 | haproxy-debugsource | before 0:3.0.5-6.el10_2.2 | 0:3.0.5-6.el10_2.2 |
| Red Hat:enterprise_linux:8::appstream | haproxy | before 0:1.8.27-5.el8_10.2 | 0:1.8.27-5.el8_10.2 |
| Red Hat:enterprise_linux:8::appstream | haproxy-debuginfo | before 0:1.8.27-5.el8_10.2 | 0:1.8.27-5.el8_10.2 |
| Red Hat:enterprise_linux:8::appstream | haproxy-debugsource | before 0:1.8.27-5.el8_10.2 | 0:1.8.27-5.el8_10.2 |
| Red Hat:enterprise_linux:9::appstream | haproxy | before 0:2.8.14-3.el9_8.2 | 0:2.8.14-3.el9_8.2 |
| Red Hat:enterprise_linux:9::appstream | haproxy-debuginfo | before 0:2.8.14-3.el9_8.2 | 0:2.8.14-3.el9_8.2 |
| Red Hat:enterprise_linux:9::appstream | haproxy-debugsource | before 0:2.8.14-3.el9_8.2 | 0:2.8.14-3.el9_8.2 |
| Red Hat:hummingbird:1 | haproxy | before 0:3.0.25-0.1.hum1 | 0:3.0.25-0.1.hum1 |
| Red Hat:rhel_aus:8.4::appstream | haproxy | before 0:1.8.27-2.el8_4.2 | 0:1.8.27-2.el8_4.2 |
| Red Hat:rhel_aus:8.4::appstream | haproxy-debuginfo | before 0:1.8.27-2.el8_4.2 | 0:1.8.27-2.el8_4.2 |
| Red Hat:rhel_aus:8.4::appstream | haproxy-debugsource | before 0:1.8.27-2.el8_4.2 | 0:1.8.27-2.el8_4.2 |
| Red Hat:rhel_aus:8.6::appstream | haproxy | before 0:1.8.27-4.el8_6.2 | 0:1.8.27-4.el8_6.2 |
+22
Same product
haproxy: all recordsOther 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 bytes53Plan
- 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 prot51Plan
- 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, a48Plan
Published before and after this one in the same product
- ← EarlierCVE-2026-33555Apr 13, 2026 · An issue was discovered in HAProxy before 3.3.6.23Monitor
- ← EarlierCVE-2026-55203Jun 18, 2026 · HAProxy - Integer Overflow in FCGI Demux Record Length Field36Monitor
- Later →CVE-2026-26080Jul 20, 2026 · HAProxy Community Edition 3.2.x through 3.3.x before 3.3.3 can enter a loop or crash because varint is mishandled.14Monitor
Remediation
Which version to upgrade to
Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.
| Product / package | Fixed version | Source |
|---|---|---|
| azl3 haproxy 2.9.11-6 on Azure Linux 3.0 | 2.9.11-7 · CBL-Mariner Releases | Microsoft (MSRC) |
| azl3 haproxy 2.9.11-7 on Azure Linux 3.0 | 2.9.11-7 · CBL-Mariner Releases | Microsoft (MSRC) |
| almalinux:haproxy | 3.0.5-6.el10_2.2 · AlmaLinux:10 | Package registry (OSV) |
| debian:haproxy | 3.2.20-1 · Debian:14 | Package registry (OSV) |
| opensuse:haproxy | 3.4.0+git31.fc300e9f2-1.1 · openSUSE:Tumbleweed | Package registry (OSV) |
| red hat:haproxy | 0:3.0.25-0.1.hum1 · Red Hat:hummingbird:1 | Package registry (OSV) |
| red hat:haproxy-debuginfo | 0:3.0.5-6.el10_2.2 · Red Hat:enterprise_linux:10.2 | Package registry (OSV) |
| red hat:haproxy-debugsource | 0:3.0.5-6.el10_2.2 · Red Hat:enterprise_linux:10.2 | Package registry (OSV) |
| rocky linux:haproxy | 0:3.0.5-6.el10_2.2 · Rocky Linux:10 | Package registry (OSV) |
| suse:haproxy | 2.8.11+git0.01c1056a4-4.1 · SUSE:Linux Micro 6.0 | Package registry (OSV) |
Exploit status
No known public exploit
No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.
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.
No dated events beyond publication.
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 researchersFinders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.
- Tristan Madani (@TristanInSec)Talence Securityfinder
Variant candidates
Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.
No nightly-computed relations.
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
- Integrity
- Availability
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- None
- Scope
- X
Weakness class (CWE)
CWE-476 · NULL Pointer DereferenceCVSS vector
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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
nvd-secondary
Attack context
MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.
MITRE has no CAPEC/ATT&CK mapping for this CWE.
Change log
- Fix✗ → ✓
For records you follow, these changes also arrive as notifications. →
References
Show all references (1 more)Show less
Vendor advisories and official records. Exploit/PoC links are deliberately left out.