CVE-2021-40346

Exp

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.

Published: 2021-09-08 Last update: 2024-11-21 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-40346 is rated High Exploit Risk (79.2/100): CVSS High severity, with high exploitation likelihood (EPSS 92.38%, 100th percentile). 1 public exploit reference(s) are indexed (Exploit-DB). Public exploits are available—assess exposure, apply mitigations, and prioritize patching.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Public exploit references (Exploit-DB) for CVE-2021-40346

EDB-ID Source Kind Published Link
— nvd_ref exploit_tag Exploit-DB ↗

Exploit prediction scoring system (EPSS) score for CVE-2021-40346

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-03-27 93.12% 92.38% -0.74%
2 2026-03-09 92.97% 93.12% +0.15%
3 2026-03-04 — 92.97% —

Full EPSS history (65 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-40346

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
7.5 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:N)
Service keeps running; no real outage angle.
 3.9 3.6 [email protected]
5.0 2.0 MEDIUM
AV:N/AC:L/Au:N/C:N/I:P/A:N Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:L)
Exploitation conditions are straightforward and predictable.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:N)
No confidentiality impact.
Integrity impact (I:P)
Partial integrity impact.
Availability impact (A:N)
No availability impact.
 10.0 2.9 [email protected]

Weakness enumeration for CVE-2021-40346

OS Trackers for CVE-2021-40346

vendor priority summary link
debian not yet assigned CVE-2021-40346 not yet assigned priority: Debian including 1 source packages (haproxy), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2021-40346
redhat medium — https://access.redhat.com/security/cve/CVE-2021-40346
suse high CVE-2021-40346 severity important: SUSE including 12 source package names (2.0.14.2.2.10:haproxy-2.0.14-11.11.1, haproxy, …), 24 product×package rows across 24 product lines (Container ses/7.1/ceph/haproxy, HPE Helion OpenStack 8, … (24 product lines)): Fixed 13, Known Not Affected 11. https://www.suse.com/security/cve/CVE-2021-40346/
ubuntu medium CVE-2021-40346 medium priority: Ubuntu including 1 source packages (haproxy), 8 status rows across 8 suites (bionic, focal, hirsute, impish, jammy, trusty, upstream, xenial): released 4, not-affected 2, DNE 1, needs-triage 1. https://ubuntu.com/security/CVE-2021-40346

Affected software / configurations for CVE-2021-40346

Vendor Product Version Raw CPE
haproxy haproxy >= 2.0.0, < 2.0.25 cpe:2.3:a:haproxy:haproxy:*:*:*:*:*:*:*:*
haproxy haproxy >= 2.2.0, < 2.2.17 cpe:2.3:a:haproxy:haproxy:*:*:*:*:*:*:*:*
haproxy haproxy >= 2.3.0, < 2.3.14 cpe:2.3:a:haproxy:haproxy:*:*:*:*:*:*:*:*
haproxy haproxy >= 2.4.0, < 2.4.4 cpe:2.3:a:haproxy:haproxy:*:*:*:*:*:*:*:*
haproxy haproxy 2.5 cpe:2.3:a:haproxy:haproxy:2.5:dev0:*:*:*:*:*:*
haproxy haproxy 2.5 cpe:2.3:a:haproxy:haproxy:2.5:dev1:*:*:*:*:*:*
haproxy haproxy 2.5 cpe:2.3:a:haproxy:haproxy:2.5:dev2:*:*:*:*:*:*
haproxy haproxy 2.5 cpe:2.3:a:haproxy:haproxy:2.5:dev3:*:*:*:*:*:*
haproxy haproxy 2.5 cpe:2.3:a:haproxy:haproxy:2.5:dev4:*:*:*:*:*:*
haproxy haproxy 2.5 cpe:2.3:a:haproxy:haproxy:2.5:dev5:*:*:*:*:*:*
haproxy haproxy 2.5 cpe:2.3:a:haproxy:haproxy:2.5:dev6:*:*:*:*:*:*
debian debian_linux 11.0 cpe:2.3:o:debian:debian_linux:11.0:*:*:*:*:*:*:*
fedoraproject fedora 33 cpe:2.3:o:fedoraproject:fedora:33:*:*:*:*:*:*:*
fedoraproject fedora 34 cpe:2.3:o:fedoraproject:fedora:34:*:*:*:*:*:*:*

References for CVE-2021-40346

URL Tags
https://git.haproxy.org/?p=haproxy.git Patch Vendor Advisory
https://github.com/haproxy/haproxy/commit/3b69886f7dcc3cfb3d166309018e6cfec9ce2c95 Patch Third Party Advisory
https://jfrog.com/blog/critical-vulnerability-in-haproxy-cve-2021-40346-integer-overflow-enables-http-smuggling/ Exploit Mitigation Third Party Advisory
https://lists.apache.org/thread.html/r284567dd7523f5823e2ce995f787ccd37b1cc4108779c50a97c79120%40%3Cdev.cloudstack.apache.org%3E
https://lists.apache.org/thread.html/r8a58fd7a29808e5d27ee56877745e58dc4bb041b9af94601554e2a5a%40%3Cdev.cloudstack.apache.org%3E
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/A7V2IYO22LWVBGUNZWVKNTMDV4KINLFO/
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/MXTSBY2TEAXWZVFQM3CXHJFRONX7PEMN/
https://www.debian.org/security/2021/dsa-4968 Third Party Advisory
https://www.mail-archive.com/haproxy%40formilux.org
https://www.mail-archive.com/haproxy%40formilux.org/msg41114.html
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