CVE-2021-40346

HIGHNVD 7.59.0▲Elevated

7.5

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.

CVSS v3: 7.5
EG Score: 9.0(high)
EPSS: 99.7%
KEV: Not listed

Published

September 8, 2021

Last Modified

November 21, 2024

References (20)

cve@mitrehttps://git.haproxy.org/?p=haproxy.git
cve@mitrehttps://github.com/haproxy/haproxy/commit/3b69886f7dcc3cfb3d166309018e6cfec9ce2c95
cve@mitrehttps://jfrog.com/blog/critical-vulnerability-in-haproxy-cve-2021-40346-integer-overflow-enables-http-smuggling/
cve@mitrehttps://lists.apache.org/thread.html/r284567dd7523f5823e2ce995f787ccd37b1cc4108779c50a97c79120%40%3Cdev.cloudstack.apache.org%3E
cve@mitrehttps://lists.apache.org/thread.html/r8a58fd7a29808e5d27ee56877745e58dc4bb041b9af94601554e2a5a%40%3Cdev.cloudstack.apache.org%3E
cve@mitrehttps://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/A7V2IYO22LWVBGUNZWVKNTMDV4KINLFO/
cve@mitrehttps://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/MXTSBY2TEAXWZVFQM3CXHJFRONX7PEMN/
cve@mitrehttps://www.debian.org/security/2021/dsa-4968
cve@mitrehttps://www.mail-archive.com/haproxy%40formilux.org
cve@mitrehttps://www.mail-archive.com/haproxy%40formilux.org/msg41114.html
af854a3a-2127-422b-91ae-364da2661108https://git.haproxy.org/?p=haproxy.git
af854a3a-2127-422b-91ae-364da2661108https://github.com/haproxy/haproxy/commit/3b69886f7dcc3cfb3d166309018e6cfec9ce2c95
af854a3a-2127-422b-91ae-364da2661108https://jfrog.com/blog/critical-vulnerability-in-haproxy-cve-2021-40346-integer-overflow-enables-http-smuggling/
af854a3a-2127-422b-91ae-364da2661108https://lists.apache.org/thread.html/r284567dd7523f5823e2ce995f787ccd37b1cc4108779c50a97c79120%40%3Cdev.cloudstack.apache.org%3E
af854a3a-2127-422b-91ae-364da2661108https://lists.apache.org/thread.html/r8a58fd7a29808e5d27ee56877745e58dc4bb041b9af94601554e2a5a%40%3Cdev.cloudstack.apache.org%3E

Patch Availability(5)

Vendor / Ecosystem	Fixed in / Patch	Released	Source
ubuntu	vim-haproxy (2.2.9-1ubuntu0.2) @ hirsute	2026-05-26	ubuntu
redhat	haproxy-0:2.0.19-2.el7	2022-01-19	redhat
redhat	haproxy-0:2.0.16-2.el7	2022-01-12	redhat
redhat	haproxy-0:2.2.13-2.el7	2022-01-05	redhat
redhat	haproxy-0:2.2.15-2.el8	2021-11-10	redhat

Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

CWE-190Integer Overflow or Wraparound

All Vendor Advisories

(5)

Every vendor that published an advisory referencing this CVE — pulled from our cve_vendor_advisories aggregation. Click any row for the vendor's original advisory page.

Data Freshness Timeline

(refreshed 8× in last 7d / 18× in last 30d)

Every time one of our enrichment pipelines (NVD, MITRE cvelistV5, EPSS, CISA KEV, GHSA, OSV, vendor advisories) ran against this CVE. Most recent first.

2026-06-05 06:09 UTCepss_batch
2026-06-05 06:09 UTCepss_batch
2026-06-04 13:10 UTCepss_batch
2026-06-04 13:10 UTCepss_batch
2026-06-02 20:11 UTCepss_batch
2026-06-02 20:11 UTCepss_batch
2026-06-01 13:50 UTCepss_batch
2026-06-01 13:50 UTCepss_batch
2026-05-29 13:42 UTCepss_batch
2026-05-28 13:43 UTCepss_batch
2026-05-28 13:43 UTCepss_batch
2026-05-26 10:43 UTCEG score recompute
2026-05-26 10:43 UTCVendor advisory
2026-05-26 10:43 UTCGHSA enrichment
2026-05-26 07:17 UTCepss_batch
2026-05-26 07:17 UTCepss_batch
2026-05-26 07:17 UTCepss_batch
2026-05-25 08:16 UTCOSV refresh

Publicly available exploits

(4 references)

Working exploit code is in the public domain (4 GitHub PoCs). Defenders should treat patch urgency accordingly — public PoCs typically lead to mass-exploitation within 24-72 hours.

GitHub PoCVulnmachines/HAProxy_CVE-2021-40346
First seen Nov 8, 2021
HAProxy CVE-2021-40346
Open source ↗
GitHub PoCdonky16/CVE-2021-40346-POC
First seen Sep 10, 2021
CVE-2021-40346 integer overflow enables http smuggling
Open source ↗
GitHub PoCalikarimi999/CVE-2021-40346
First seen Sep 10, 2021
Open source ↗
GitHub PoCknqyf263/CVE-2021-40346
First seen Sep 8, 2021
CVE-2021-40346 PoC (HAProxy HTTP Smuggling)
Open source ↗

Frequently asked(5)

What is CVE-2021-40346?

CVE-2021-40346 is a high vulnerability published on September 8, 2021. An integer overflow exists in HAProxy 2.0 through 2.5 in htxaddheader 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.

When was CVE-2021-40346 disclosed?

CVE-2021-40346 was first published in the National Vulnerability Database on September 8, 2021, with the most recent update on November 21, 2024. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.

Is CVE-2021-40346 actively exploited?

CVE-2021-40346 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 99.7% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.

What is the CVSS score of CVE-2021-40346?

CVE-2021-40346 has a CVSS v3 base score of 7.5 (NVD). EchelonGraph synthesises NVD + CISA KEV + FIRST EPSS + GHSA into a combined EG score of 9.0.

How do I remediate CVE-2021-40346?

Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-40346, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

See which npm, PyPI, Go, and Maven packages are affected by CVE-2021-40346

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CVE-2021-40346

Published

Last Modified

References (20)

Patch Availability(5)

Weakness Classification(1)

All Vendor Advisories

Data Freshness Timeline

Publicly available exploits

Frequently asked(5)

Dependency Blast Radius

Is Your Infrastructure Affected by CVE-2021-40346?

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CVE-2021-40346

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🔄 Last Modified

🔗 References (20)

Patch Availability(5)

Weakness Classification(1)

All Vendor Advisories

Data Freshness Timeline

Publicly available exploits

❓ Frequently asked(5)

Dependency Blast Radius

Is Your Infrastructure Affected by CVE-2021-40346?

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References (20)

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