What is CVE-2021-38751?

CVE-2021-38751 is a medium-severity vulnerability in Exponentcms, classified under Improper Encoding or Escaping of Output. CVSS score: 4.3/10. Published 2021-08-16.

How severe is CVE-2021-38751?

Medium severity. CVSS v3 base score is 4.3 out of 10.

Is CVE-2021-38751 known to be exploited?

3 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.

Vulnerability in Exponentcms

CVE-2021-38751

A HTTP Host header attack exists in ExponentCMS 2.6 and below in /exponent_constants.php. A modified HTTP header can change links on the webpage to an arbitrary value, leading to a possible attack vector for MITM.

Published 2021-08-16 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 4.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N.

EPSS exploit prediction

EPSS: 0.025 (83.9th percentile), scored 2026-09-30.

Low probability of exploitation in the next 30 days, but still tracked. 84th percentile — 83.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.025 · newest: 0.025 · change: 0.000

Affected products

Exponentcms

Weakness classification (CWE)

CWE-116 — Improper Encoding or Escaping of Output

Public proof-of-concept exploits

References

github.com/exponentcms/exponent-cms/issues/1544 (Exploit, Third Party Advisory, Issue Tracking)

Frequently asked questions

What is CVE-2021-38751?: CVE-2021-38751 is a medium-severity vulnerability in Exponentcms, classified under Improper Encoding or Escaping of Output. CVSS score: 4.3/10. Published 2021-08-16.
How severe is CVE-2021-38751?: Medium severity. CVSS v3 base score is 4.3 out of 10.
Is CVE-2021-38751 known to be exploited?: 3 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.