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...

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.

Metrics

CVSS 3.1

7.5/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

EPSS Probability

2.30%

81.1th percentile

Probability of exploitation in the next 30 days. Learn more

Affected Software

Vendor	Product	Versions
Haproxy	Haproxy	>= 2.2.0, < 2.2.16
Haproxy	Haproxy	>= 2.3.0, < 2.3.13
Haproxy	Haproxy	>= 2.4.0, < 2.4.3
Debian	Debian Linux	11.0
Fedoraproject	Fedora	33
Fedoraproject	Fedora	34

References

Timeline

Published: Aug 17, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is 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.

How severe is CVE-2021-39240?

CVE-2021-39240 has a CVSS score of 7.5/10 (HIGH severity). The EPSS model estimates a 2.30% probability of exploitation in the next 30 days.

How do I fix CVE-2021-39240?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.