How severe is CVE-2021-40346?

CVE-2021-40346 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity high, and availability none.

Is CVE-2021-40346 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 58% (99th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-40346?

CVE-2021-40346 primarily affects Haproxy. In total, 11 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-40346?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2021-40346 published?

CVE-2021-40346 was published on 2021-09-08 and last updated on 2026-06-17.

CVE-2021-40346

CVE-2021-40346 is a high-severity vulnerability in Haproxy with a CVSS 3.x base score of 7.5. Its EPSS exploit-prediction score of 58% places it in the 99th percentile, indicating an elevated likelihood of exploitation. The underlying weakness is classified as CWE-190.

Key facts

Severity: High (CVSS 3.x base score 7.5)
CVSS v2: 5.0
EPSS exploit prediction: 58% (99th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-190
Affected product: Haproxy
Published: 2021-09-08
Last modified: 2026-06-17

Description

An 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, allowing an attacker to bypass all configured http-request HAProxy ACLs and possibly other ACLs.

Frequently asked questions

What is CVE-2021-40346?: An 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, allowing an attacker to bypass all configured http-request HAProxy ACLs and possibly other ACLs.
How severe is CVE-2021-40346?: CVE-2021-40346 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity high, and availability none.
Is CVE-2021-40346 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 58% (99th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-40346?: CVE-2021-40346 primarily affects Haproxy. In total, 11 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-40346?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2021-40346 published?: CVE-2021-40346 was published on 2021-09-08 and last updated on 2026-06-17.

References

Affected products (11)

cpe:2.3:a:haproxy:haproxy:*:*:*:*:*:*:*:*
cpe:2.3:a:haproxy:haproxy:2.5:dev0:*:*:*:*:*:*
cpe:2.3:a:haproxy:haproxy:2.5:dev1:*:*:*:*:*:*
cpe:2.3:a:haproxy:haproxy:2.5:dev2:*:*:*:*:*:*
cpe:2.3:a:haproxy:haproxy:2.5:dev3:*:*:*:*:*:*
cpe:2.3:a:haproxy:haproxy:2.5:dev4:*:*:*:*:*:*
cpe:2.3:a:haproxy:haproxy:2.5:dev5:*:*:*:*:*:*
cpe:2.3:a:haproxy:haproxy:2.5:dev6:*:*:*:*:*:*
cpe:2.3:o:debian:debian_linux:11.0:*:*:*:*:*:*:*
cpe:2.3:o:fedoraproject:fedora:33:*:*:*:*:*:*:*
cpe:2.3:o:fedoraproject:fedora:34:*:*:*:*:*:*:*

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Other CWE-190 (Integer Overflow or Wraparound) vulnerabilities

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CVE-2025-64721 — Critical (CVSS 10.0): Sandboxie is a sandbox-based isolation software for 32-bit and 64-bit Windows NT-based operating systems. In versions…
CVE-2015-5108 — Critical (CVSS 10.0): Integer overflow in Adobe Reader and Acrobat 10.x before 10.1.15 and 11.x before 11.0.12, Acrobat and Acrobat Reader DC…
CVE-2015-5097 — Critical (CVSS 10.0): Integer overflow in Adobe Reader and Acrobat 10.x before 10.1.15 and 11.x before 11.0.12, Acrobat and Acrobat Reader DC…
CVE-2013-2555 — Critical (CVSS 10.0): Integer overflow in Adobe Flash Player before 10.3.183.75 and 11.x before 11.7.700.169 on Windows and Mac OS X, before…

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