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Fencer Intel
critical 9.0

CVE-2026-121491 json

Fiber Admin 3.1.0 - 4.0.0 - Unauthenticated RCE via Host Header

published 2d ago modified 2d ago also EUVD-2026-118943

cvss
9.0
version 3.1, CISA ADP
cisa kev
Not listed
not in CISA's catalog
epss
0.4%
EPSS 0.4% chance of exploitation in 30 days, percentile 33%
public exploits
0
none known

Summary

The Fiber Admin WordPress plugin before 4.0.1 does not validate or escape a request header before writing it into a PHP file it regenerates on an unprotected admin hook, allowing unauthenticated attackers to execute arbitrary code when its custom database error page is enabled and they win a race against an administrator saving its settings.

Patch / fix

  • Unknown Fiber Admin 4.0.1

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CISA SSVC

Exploitation
none
Automatable
no
Technical impact
total
Assessed
2d ago

Exploit prediction

0.40% chance of exploitation in the next 30 days, higher than 33% of all scored CVEs (FIRST EPSS, 2026-11-09).

Exploits and checks

  • wpscan.com https://wpscan.com/vulnerability/42b9773d-9c69-4435-be20-ae86f52b4608/ referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CISA ADP 3.1 9.0 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H

Affected products

  • Unknown Fiber Admin

Classification

Weakness
  • CWE-94 Improper Control of Generation of Code
Technology feeds

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.