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.

Multiple Vulnerabilities in HaProxy

It is, therefore, affected by a vulnerability as referenced in the ALAS2023-2026-1915 advisory.

    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.
    (CVE-2026-55204)

Tenable has extracted the preceding description block directly from the tested product security advisory.

Note that Nessus has not tested for this issue but has instead relied only on the application's self-reported version number.

The remote openSUSE 16 host has a package installed that is affected by multiple vulnerabilities as referenced in the openSUSE-SU-2026:21245-1 advisory.

    This update for haproxy fixes the following issues

    - Update to version 3.2.21+git0.dbe43be37
    - CVE-2026-55203: integer overflow vulnerability in the fcgi_conn structure's drl field that allows buffer     misparse as new FCGI record headers (bsc#1268557).
    - CVE-2026-55204: null pointer dereference vulnerability in hpack_dht_insert() within src/hpack-tbl.c     (bsc#1268558).

Tenable has extracted the preceding description block directly from the SUSE security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The version of Tencent Linux installed on the remote TencentOS Server 4 host is prior to tested version. It is, therefore, affected by a vulnerability as referenced in the TSSA-2026:0548 advisory.

    Package updates are available for TencentOS Server 4 that fix the following vulnerabilities:

    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.

Tenable has extracted the preceding description block directly from the Tencent Linux security advisory.

Note that Nessus has not tested for this issue but has instead relied only on the application's self-reported version number.

The remote SUSE Linux SLES15 host has a package installed that is affected by multiple vulnerabilities as referenced in the SUSE-SU-2026:2652-1 advisory.

    This update for haproxy fixes the following issues

    - CVE-2026-55203: integer overflow vulnerability in the fcgi_conn structure's drl field that allows buffer     misparse as       new FCGI record headers (bsc#1268557).
    - CVE-2026-55204: null pointer dereference vulnerability in hpack_dht_insert() within src/hpack-tbl.c     (bsc#1268558).

Tenable has extracted the preceding description block directly from the SUSE security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The remote SUSE Linux SLES15 host has a package installed that is affected by multiple vulnerabilities as referenced in the SUSE-SU-2026:2651-1 advisory.

    This update for haproxy fixes the following issues

    - CVE-2026-55203: integer overflow vulnerability in the fcgi_conn structure's drl field that allows buffer     misparse as       new FCGI record headers (bsc#1268557).
    - CVE-2026-55204: null pointer dereference vulnerability in hpack_dht_insert() within src/hpack-tbl.c     (bsc#1268558).

Tenable has extracted the preceding description block directly from the SUSE security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The remote Ubuntu 22.04 LTS / 24.04 LTS / 25.10 / 26.04 LTS host has packages installed that are affected by multiple vulnerabilities as referenced in the USN-8459-1 advisory.

    It was discovered that HAProxy incorrectly handled the FCGI demultiplexer record length field. A remote     attacker could possibly use this issue to cause incorrect request routing, response smuggling, or other     memory safety issues. (CVE-2026-55203)

    It was discovered that HAProxy failed to validate the return value of the HPACK dynamic table     defragmentation function when memory was exhausted. A remote attacker could possibly use this issue to     cause HAProxy to crash, resulting in a denial of service. (CVE-2026-55204)

Tenable has extracted the preceding description block directly from the Ubuntu security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The Linux/Unix host has one or more packages installed that are impacted by a vulnerability without a vendor supplied patch available.

  - 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.
    (CVE-2026-55204)

Note that Nessus relies on the presence of the package as reported by the vendor.

ID	Name	Product	Family	Severity
327400	Amazon Linux 2023 : haproxy (ALAS2023-2026-1915)	Nessus	Amazon Linux Local Security Checks	high
326036	openSUSE 16 Security Update : haproxy (openSUSE-SU-2026:21245-1)	Nessus	SuSE Local Security Checks	critical
325864	TencentOS Server 4: haproxy (TSSA-2026:0548)	Nessus	Tencent Local Security Checks	high
323245	SUSE SLES15 Security Update : haproxy (SUSE-SU-2026:2652-1)	Nessus	SuSE Local Security Checks	critical
323243	SUSE SLES15 Security Update : haproxy (SUSE-SU-2026:2651-1)	Nessus	SuSE Local Security Checks	critical
322262	Ubuntu 22.04 LTS / 24.04 LTS / 25.10 / 26.04 LTS : HAProxy vulnerabilities (USN-8459-1)	Nessus	Ubuntu Local Security Checks	critical
321740	Linux Distros Unpatched Vulnerability : CVE-2026-55204	Nessus	Misc.	high

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