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Fencer Intel
medium 4.3

CVE-2021-38751 json

A HTTP Host header attack exists in ExponentCMS 2.6 and below in /exponent_constants.php.

published 5y ago modified 4mo ago also EUVD-2021-25188

cvss
4.3
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
2.5%
EPSS 2.5% chance of exploitation in 30 days, percentile 84%
public exploits
0
none known, plus a Nuclei check

Summary

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.

Patch / fix

  • exponentcms exponentcms 2.6

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Exploit prediction

2.47% chance of exploitation in the next 30 days, higher than 84% of all scored CVEs (FIRST EPSS, 2026-11-09).

Exploits and checks

  • Nuclei template ExponentCMS <= 2.6 - Host Header Injection nuclei detection template
  • github.com https://github.com/exponentcms/exponent-cms/issues/1544 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
NVD 3.1 4.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N
NVD 2.0 4.3 AV:N/AC:M/Au:N/C:N/I:P/A:N

Classification

Weakness
  • CWE-116 Improper Encoding or Escaping of Output

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.