CVE-2021-40346
HighAn 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 Mar 15, 2022 · Updated Oct 3, 2026 · Also known as BIT-haproxy-2021-40346, DEBIAN-CVE-2021-40346, DSA-4968-1, SUSE-SU-2021:2975-1, SUSE-SU-2021:3257-1, SUSE-SU-2021:3258-1, UBUNTU-CVE-2021-40346, USN-5063-1
Key Facts
Patch immediately- CVE-2021-40346 is a high-severity vulnerability (CVSS 7.5 v3.1) affecting Haproxy, Debian Linux, Fedora (Fedoraproject) and 1 more product.
- It is not listed in any known-exploited vulnerabilities catalog. No public exploit code is known.
- EPSS estimates a 59% probability of exploitation in the next 30 days.
- Fixed versions are available, including Haproxy 0:2.2.13-2.el7, Haproxy 0:2.2.15-2.el8, Haproxy 2.0.10-3.ph1.
- Brandefense priority: patch immediately, because it is very likely to be exploited soon.
CVSS v3.1
7.5
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
EPSS (30-day exploit likelihood)
59%
Higher than 99.1% of all scored CVEs
Exploited in the wild
No known
Not in a known-exploited catalog
Public exploit code
None known
Get the full CVE-2021-40346 brief as a PDF
Every affected product and fixed release, exploitation status and a first 24 hours response checklist, emailed within minutes.
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.
Affected Products
45 affected entries in total| Product | Affected versions | Fixed in |
|---|---|---|
| HaproxyHaproxy | 2.5-dev0, 2.5-dev1, 2.5-dev2, 2.5-dev3, 2.5-dev4, 2.5-dev5, 2.5-dev6, >= 2.0.0 | 2.0.25 |
| Debian LinuxDebian | 11.0 | n/a |
| FedoraFedoraproject | 33, 34 | n/a |
| haproxy-docphoton | See advisory | 2.3.4-4.ph4 |
Patched Releases
Haproxy
0:2.2.13-2.el7, 0:2.2.15-2.el8, 2.0.10-3.ph1, 2.0.10-3.ph2, 2.0.13-2ubuntu0.3, 2.0.14-11.11.1, 2.0.14-3.31.1, 2.0.14-8.23.1, 2.0.14-lp152.2.6.1, 2.0.25, 2.2.16-3, 2.2.17, 2.2.6-3.ph3, 2.2.9-2+deb11u2, 2.2.9-2ubuntu2, 2.3.14, 2.3.4-4.ph4, 2.4.4, 2.4.4-1, 2.4.4+git0.acb1d0bea-1.2
haproxy-doc
2.3.4-4.ph4
Timeline
Publicly disclosed
Mar 15, 2022
Last updated
Oct 3, 2026
Weakness Type
- CWE-190 Integer Overflow or Wraparound
- CWE-444 Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
References
- advisoryRHSA-2021:4118
- advisoryRHSA-2021:5208
- advisoryRHSA-2022:0024
- advisoryRHSA-2022:0114
- advisoryhttps://access.redhat.com/security/cve/CVE-2019-13750
FAQ
Common Questions.
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.
Affected: Haproxy versions 2.5-dev0, 2.5-dev1, 2.5-dev2, 2.5-dev3, 2.5-dev4, 2.5-dev5, 2.5-dev6, >= 2.0.0; Debian Linux versions 11.0; Fedora (Fedoraproject) versions 33, 34, among others. The full list is in the CVE brief.
It is not listed in any known-exploited vulnerabilities catalog.
No, it is not currently listed in the CISA Known Exploited Vulnerabilities catalog.
No public exploit code is known.
Fixed versions are available, including Haproxy 0:2.2.13-2.el7, Haproxy 0:2.2.15-2.el8, Haproxy 2.0.10-3.ph1.
Brandefense priority: patch immediately, because it is very likely to be exploited soon.
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