HOMEVULNERABILITIESCVE-2021-39240
HIGH

CVE-2021-39240

NVD-CWE-noinfoPublished: August 17, 2021· Updated: Jun 17, 2026

7.5
CVSS v3.1

Official Description

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.

NVD Source

Technical Analysis

CVE-2021-39240 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.

The vulnerability requires no privileges and no user interaction, making it a prime target for automated exploitation campaigns and worm-like propagation.

A successful exploit results in complete confidentiality breach (data exposure), with a CVSS base score of 7.5.

CVSS v3.1 Vector Breakdown

Exploitability
Attack VectorNetwork
Attack ComplexityLow
Privileges Req.None
User InteractionNone
ScopeUnchanged
Impact
ConfidentialityHigh
IntegrityNone
AvailabilityNone
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

Affected Vendors & Products

Debian1 product(s)
debian linux
Fedora1 product(s)
fedora
haproxy1 product(s)
haproxy
Source: NVD CPE · 4 total CPE entries

Exploit & PoC Resources

NO KNOWN EXPLOITNo public exploit confirmed at this time
Exploit-DB
Offensive Security exploit database
GitHub PoC Search
Community PoC repositories
Rapid7 / Metasploit
Metasploit module search
PacketStorm
Security advisories & exploits
NVD Detail
Official NIST entry
MITRE CVE
CVE Program entry
External links open in a new tab. Always verify in a controlled environment before use.

Official Patches & Advisories

ADVISORYhttps://www.debian.org/security/2021/dsa-4960
ADVISORYhttps://www.debian.org/security/2021/dsa-4960

All References (12)

→
https://git.haproxy.org/?p=haproxy.git%3Ba=commit%3Bh=4b8852c70d8c4b7e225e24eb58258a15eb54c26e
→
https://git.haproxy.org/?p=haproxy.git%3Ba=commit%3Bh=a495e0d94876c9d39763db319f609351907a31e8
→
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/4ALECUZDIMT5FYGP6V6PVSI4BKVZTZWN/
→
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/RPNY4WZIQUAUOCLIMUPC37AQWNXTWIQM/
→
https://www.debian.org/security/2021/dsa-4960Third Party Advisory
→
https://www.mail-archive.com/haproxy%40formilux.org/msg41041.html
→
https://git.haproxy.org/?p=haproxy.git%3Ba=commit%3Bh=4b8852c70d8c4b7e225e24eb58258a15eb54c26e
→
https://git.haproxy.org/?p=haproxy.git%3Ba=commit%3Bh=a495e0d94876c9d39763db319f609351907a31e8
→
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/4ALECUZDIMT5FYGP6V6PVSI4BKVZTZWN/
→
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/RPNY4WZIQUAUOCLIMUPC37AQWNXTWIQM/
→
https://www.debian.org/security/2021/dsa-4960Third Party Advisory
→
https://www.mail-archive.com/haproxy%40formilux.org/msg41041.html

Quick Facts

CVE IDCVE-2021-39240
CVSS Score7.5 / 10
SeverityHIGH
WeaknessNVD-CWE-noinfo
CISA KEVNo
Affected3 vendor(s)
PublishedAug 17, 2021

Related CVEs (NVD-CWE-noinfo)

CVE-2017-3623
10.0
CVE-2015-5895
10.0
CVE-2009-1314
10.0
CVE-2008-5010
10.0
CVE-2015-3042
10.0
CVE-2014-2624
10.0

Recommended Actions

  • →Apply vendor patches immediately
  • →Monitor CVE-2021-39240 in threat intel feeds
  • →Review IDS/IPS signatures for exploitation attempts
Data sourced from NVD (NIST), CISA KEV, and EPSS (FIRST). Analysis generated by CTIWatch. CVE data is provided under the NVD usage policy.
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