#VU55970 Input validation error in HAProxy - CVE-2021-39241

Vulnerability identifier: #VU55970

Vulnerability risk: Medium

CVSSv4.0: 2.7 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N/E:U/U:Green]

CVE-ID: CVE-2021-39241

CWE-ID: CWE-20

Exploitation vector: Network

Exploit availability: No

Vulnerable software:
HAProxy
Server applications / IDS/IPS systems, Firewalls and proxy servers

Vendor: HAProxy

Description

The vulnerability allows a remote attacker to bypass implemented security restrictions.

The vulnerability exists due to insufficient validation of user-supplied input in HAProxy.  An HTTP method name may contain a space followed by the name of a protected resource. It is possible that a server would interpret this as a request for that protected resource, such as in the "GET /admin? HTTP/1.1 /static/images HTTP/1.1" example.

The attacker can abuse such behavior to bypass implemented security restrictions and perform unauthorized actions against the web application behind the HAProxy.

Mitigation
Install updates from vendor's website.

Vulnerable software versions

HAProxy: 2.0.0 - 2.0.23, 2.2.0 - 2.2.15, 2.3.0 - 2.3.12, 2.4.0 - 2.4.2

---

External links
https://www.mail-archive.com/haproxy@formilux.org/msg41041.html
https://git.haproxy.org/?p=haproxy.git;a=commit;h=89265224d314a056d77d974284802c1b8a0dc97f

---

Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote non-authenticated attacker via the Internet.

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability.