Fiber Admin 3.1.0 - 4.0.0 - Unauthenticated RCE via Host Header
- Exploited
- No known exploitation
- Fix
- Fixed in 4.0.1
- Who is exposed
- Not reported
Do first: Upgrade to a fixed version: 4.0.1.
- Last modified
- FIRST's estimate of the chance attackers exploit it in the next 30 days, updated daily.What do these mean? →
- 0.22% · 13th percentile
- A 0-100 score for how much a CVE matters across the industry: exploitation, exposure, how widely the software is used, severity and whether a fix exists.What do these mean? →
- 27/100 · provisional
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
- Exploitation: none
- Automatable: no
- Technical impact: total
Summary
The Fiber Admin WordPress plugin does not validate a request header before writing it into a PHP file, which lets unauthenticated attackers execute arbitrary code on the site. The flaw is reachable only when the plugin's custom database error page is enabled and the attacker wins a race against an administrator saving the plugin's settings.
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
Read the original description
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.
cve.now Index
- Exploitation0/40No signal
- Exposure17/25No login or user action needed per the CVSS vector, reachable over the network without a login · Unknown: No advisory context yet
- Reach?/20Unknown. No tracked technology or package matched
- Severity10/10CVSS 9.0, total technical impact per CISA
- No patch0/5No signal
What would change the score
- Would score about 72 if added to CISA KEV
- Would score about 67 if CISA's SSVC rates exploitation active
- Would score about 32 if advisories confirm default setups are exposed
What to do
Upgrade to a fixed version: 4.0.1.
Timeline
- CVE published
- First seen by cve.now
- CISA SSVC assessment
Exploitation: none · Automatable: no · Technical impact: total
- Record last updated
- Posted on X by cve.now
Affected versions
- Unknown Fiber Admin
From 3.1.0 · fixed in 4.0.1
Evidence 1
- Exploit
Corrections
None so far.
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Questions about CVE-2026-121491
Is CVE-2026-121491 being exploited?
It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.Source: cve.now feed data
Which versions are affected by CVE-2026-121491?
Fiber Admin: from 3.1.0 before 4.0.1.Source: cve.now feed data
How do I fix CVE-2026-121491?
Upgrade to a fixed version: 4.0.1.Source: cve.now feed data