# CVE-2026-55204 — haproxy

> As of 2026-06-18, CVE-2026-55204 is a HIGH-severity vulnerability in haproxy, CVSS v3.1 7.5. No Threadlinqs-tracked threat campaign has been attributed to CVE-2026-55204 as of 2026-06-18; the identifier is re-checked against the Threadlinqs threat corpus on every daily ingest.

**Last updated:** 2026-06-18

## What is CVE-2026-55204?

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.

The record classifies CVE-2026-55204 under weakness class [CWE-476](https://intel.threadlinqs.com/cwe/CWE-476). Its CVSS v3 base vector states that the flaw is reachable remotely over the network, needs no prior authentication, needs no user interaction, and has high impact on availability. 1 affected-product entry is recorded, across 1 vendor, listed below. The identifier was first published 109 days ago.

## Severity and exploitation probability

- **CVSS v3.1 base score:** 7.5 — HIGH (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **CVSS v4.0 base score:** 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`)
- **CISA KEV:** Not listed in the CISA Known Exploited Vulnerabilities catalog
- **Threadlinqs priority:** 3.8/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
- **Published:** 2026-06-18

## Is CVE-2026-55204 being exploited?

It currently carries a trending score of 30 in the Threadlinqs vulnerability feed.

## Affected products and versions

- **haproxy**: haproxy

## How to fix CVE-2026-55204

No vendor patch reference has been recorded for CVE-2026-55204 in the tracked sources. Follow the references below for a fix, and treat the products listed above as exposed until the vendor states otherwise.

## Threat activity tracking CVE-2026-55204

No threat campaign in the Threadlinqs corpus currently references CVE-2026-55204, in its CVE list or as an indicator. The linkage is recomputed from the live corpus on every daily ingest, so this section fills in as soon as a tracked campaign cites the identifier.

## Sources

Enriched from CVE.org. Last verified by Threadlinqs on 2026-06-19.

**Vendor advisory and patch**

- [github.com — patch](https://github.com/haproxy/haproxy/commit/9a6d1fe3f00d86ab4ea6ea6ea0a5d48fc058a513)

**Third-party advisory**

- [vulncheck.com — third party advisory](https://www.vulncheck.com/advisories/haproxy-null-pointer-dereference-in-hpack-dht-insert-function)

Canonical: https://intel.threadlinqs.com/cve/CVE-2026-55204
Full detection coverage and IOCs for threats exploiting CVE-2026-55204 via the Threadlinqs MCP server (Purple tier): https://intel.threadlinqs.com/mcp