CVE-2021-39240

An issue was discovered in HAProxy 2.2 before 2.2.16, 2.3 before 2.3.13, and 2.4 before 2.4.3. It does not ensure that the scheme and path portions of a URI have the expected characters. For example, the authority field (as observed on a target HTTP/2 server) might differ from what the routing rules were intended to achieve.

Published: 2021-08-17 Last update: 2024-11-21 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-39240 is rated Moderate Risk (60.6/100): CVSS High severity, with medium exploitation likelihood (EPSS 2.30%). EPSS rose +2.24% over the last day, indicating growing attacker interest. Review affected assets and schedule remediation.

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

Exploit prediction scoring system (EPSS) score for CVE-2021-39240

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 2026-06-15 0.06% 2.30% +2.24%
2 2025-03-17 0.59% 0.06% -0.52%
3 2024-12-17 — 0.59% —

Full EPSS history (11 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-39240

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:H/I:N/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:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
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:P/I:N/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:P)
Partial confidentiality impact.
Integrity impact (I:N)
No integrity impact.
Availability impact (A:N)
No availability impact.
 10.0 2.9 [email protected]

Weakness enumeration for CVE-2021-39240

OS Trackers for CVE-2021-39240

vendor priority summary link
debian not yet assigned CVE-2021-39240 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-2021-39240
redhat medium — https://access.redhat.com/security/cve/CVE-2021-39240
suse high CVE-2021-39240 severity important: SUSE including 7 source package names (haproxy, haproxy-2.4.22+git0.f8e3218e2-150400.3.16.1, …), 21 product×package rows across 21 product lines (HPE Helion OpenStack 8, SUSE Linux Enterprise High Availability Extension 12 SP3, … (21 product lines)): Known Not Affected 15, Fixed 6. https://www.suse.com/security/cve/CVE-2021-39240/
ubuntu medium CVE-2021-39240 medium priority: Ubuntu including 1 source packages (haproxy), 8 status rows across 8 suites (bionic, focal, hirsute, impish, jammy, trusty, upstream, xenial): not-affected 3, released 3, DNE 1, needs-triage 1. https://ubuntu.com/security/CVE-2021-39240

Affected software / configurations for CVE-2021-39240

Vendor Product Version Raw CPE
haproxy haproxy >= 2.2.0, < 2.2.16 cpe:2.3:a:haproxy:haproxy:*:*:*:*:*:*:*:*
haproxy haproxy >= 2.3.0, < 2.3.13 cpe:2.3:a:haproxy:haproxy:*:*:*:*:*:*:*:*
haproxy haproxy >= 2.4.0, < 2.4.3 cpe:2.3:a:haproxy:haproxy:*:*:*:*:*:*:*:*
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-2021-39240

cvelogic Threat Intelligence