#VU55969 Input validation error in HAProxy - CVE-2021-39240

Vulnerability identifier: #VU55969

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-2021-39240

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 security restrictions.

The vulnerability exists due to insufficient validation of user-supplied input when processing HTTP/2 requests. HAProxy does not ensure that the scheme and path portions of a URI have the expected characters, e.g. the authority field on a target HTTP/2 server might differ from what the routing rules were intended to achieve. A remote attacker can send specially crafted input to the application and bypass implemented security restrictions.

Mitigation
Install updates from vendor's website.

Vulnerable software versions

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

---

External links
https://git.haproxy.org/?p=haproxy.git;a=commit;h=a495e0d94876c9d39763db319f609351907a31e8
https://git.haproxy.org/?p=haproxy.git;a=commit;h=4b8852c70d8c4b7e225e24eb58258a15eb54c26e
https://www.mail-archive.com/haproxy@formilux.org/msg41041.html

---

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.