CVE-2026-54089

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File Browser is a file managing interface for uploading, deleting, previewing, renaming, and editing files within a spec

File Browser is a file managing interface for uploading, deleting, previewing, renaming, and editing files within a specified directory. Starting with 2.0.0-rc.1, when FileBrowser is configured with proxy authentication (auth.method=proxy), any unauthenticated attacker who can reach the server directly can impersonate any user - including admin - by sending a single forged HTTP header. No credentials are required.

Additionally, specifying a non-existent username causes the server to automatically create a new user account, providing an account creation primitive with no authorization. This is an already known issue that has been documented in the documentation for several years, but has not been documented as a vulnerability before.

CRITICAL · CVSS 9.1 EPSS 0.00337

EPSS exploitation odds0.34% · top 74%

Schedule remediation

SSVC automatable: yes - attacks can be scripted at scale
CVSS base score ≥ 7.0

No Sigma yet — build one → YARA rules0

Look this up elsewhere - one-click external pivots

NVD CVE.org CISA Exploit-DB GitHub PoC VulnCheck KEV GreyNoise

▸ How to read a CVE - triage first, then detect and patch

This page is every public fact about CVE-2026-54089, cross-linked. Its job is to answer one question fast - does this need my attention now? - and then hand you the two things you do about it. Here is how an analyst reads it.

Triage: should I act now? Four signals, and they are not interchangeable:

CVSSseverity - how bad it is IF exploited, 0-10. A high CVSS alone is not urgency; a flaw can be a perfect 10 and never actually be attacked. EPSSprobability - a model’s estimate of the chance it is exploited in the next 30 days, 0-1. This is the “will it actually happen” signal. CISA KEVconfirmed - it is being exploited in the wild right now. The strongest signal on the page; KEV beats any score. Weaponisedavailability - public exploits / PoCs, and especially Metasploit modules rated Excellent / Great. Reliable, packaged exploit code means low-skill attackers can use it today.

How they combine: KEV, or a dependable Metasploit module, means patch now regardless of CVSS. High CVSS + low EPSS + no exploit is real but not an emergency - schedule it. Low CVSS but KEV-listed still gets patched now. The verdict above already weighed these for you; this is how it got there.

Then what - two workflows:

Detectwhen you cannot patch today, follow this CVE to the ATT&CK techniques it enables, then Build a SIEM detection (the green button) - author a rule, test it in Atomic, deploy it. That buys visibility while the patch waits. PatchAffected products / packages tell you if you are exposed; Fixed versions by distribution and Vendor advisories give the exact version that closes it.

Reading order for the panels below: verdict + badges, then Public exploits / Metasploit (is it weaponised), then ATT&CK techniques + Sigma / IDS rules (can I detect it), then Affected products / packages + Fixed versions (am I exposed, what patches it), then Threat actors / IOCs (who uses it), then Scoring & timeline / references (the evidence).

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Exploitation evidence

1 of 7 sources

Corroboration score 8/100 · emerging. This counts how many independent sources have exploitation evidence, and separates two different things: confirmed in-the-wild use (CISA KEV, Microsoft MSRC, ransomware activity) from exploit / PoC availability (Metasploit, ExploitDB, Nuclei, public PoCs). A template or PoC existing means an attack is possible and easy - it is not, on its own, proof the CVE is being exploited in the wild.

Exploit / PoC available

public PoC

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Severity & exploitation scoring

View on NVD →

CVSS base score

9.1

CRITICALCVSS v3.1 · [email protected]

EPSS exploitation probability

0.34%

Top 74%odds of exploitation in the next 30 days

CVSS metric silhouette

shape grows toward worst-case

SSVC triage · cisa-vulnrichment

Exploitation

poc

Automatable

yes

Tech impact

total

CVSS vector breakdown

Exploitability - how they get in

Attack Vector

Network Adjacent Local Physical

Attack Complexity

Low High

Privileges Required

None Low High

User Interaction

None Required

Scope

Unchanged Changed

Impact - what breaks

Confidentiality

None Low High

Integrity

None Low High

Availability

None Low High

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

Attack path

Full kill chain

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ATT&CK techniques

Techniques this CVE enables. Pills with a solid outline are high confidence - named directly in ATT&CK or Nuclei, or human-curated by CTID; the rest are inferred from the weakness type using MITRE's CVE Mapping Methodology and the CWE → CAPEC chain. Broad, generic-weakness guesses are filtered out. A small N× marks a technique that N independent sources agree on.

T1036.001 · Invalid Code Signature T1134 · Access Token Manipulation T1134.001 · Token Impersonation/Theft T1528 · Steal Application Access Token T1539 · Steal Web Session Cookie T1550.004 · Web Session Cookie T1553.002 · Code Signing T1557 · Adversary-in-the-Middle

▤ Build a SIEM detection for these techniques