CVE Tools
Sign in

CVE-2026-6686

FatFs Use of Uninitialized Clusters After Seek Past EOF

Published: Jul 1, 2026Updated: Jul 2, 2026 Sources: CVE List NVDCWE-908
4.6MEDIUM
NVD MITRE
EPSS Score
0.2%
Top 92.6%
CISA KEV
Not in KEV
Exploits
No Known Exploits
Remediation
No Fix Available
Self-Check
Not available

Description

FatFs R0.16 and earlier contains an uninitialized cluster exposure when f_lseek() extends files beyond EOF without zero-filling newly allocated clusters. This maps to CWE-908 (Use of Uninitialized Resource). Estimated CVSS v3.1 vector: CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N (4.6, Medium). The estimated CISA SSVC vectors are Exploitation: PoC, Technical Impact: Partial.

No summary for this CVE yet.

CVSS Vector Breakdown

AV:PAC:LPR:NUI:NS:UC:HI:NA:N
Exploitability
AV:PAttack Vector
Physical
AC:LAttack Complexity
Low
PR:NPrivileges Required
None
UI:NUser Interaction
None
Scope
S:UScope
Unchanged
Impact
C:HConfidentiality
High
I:NIntegrity
None
A:NAvailability
None
Open in CVSS calculator →

Weaknesses

CWE-908

Affected Products

ChaN
FatFs
elm-chan
fatfs

Exploitability

No known exploits, KEV entries, or remediation guidance available for this vulnerability yet.

Attack Graph

Products CVE Techniques Tactics

Click technique nodes for MITRE ATT&CK details · drag to pan · Ctrl/⌘ + scroll to zoom, or go fullscreen.

MITRE ATT&CK

1 technique
Collection
View detailed technique mapping

References

https://www.runzero.com/blog/fatfs-bugs/
runzero.com
https://github.com/runZeroInc/vulns-2026-fatfs-chance
github.com
https://elm-chan.org/fsw/ff/
elm-chan.org
and 1 more references View all →
News mentions
1

Unlock Complete Vulnerability Intelligence

Get the full picture for CVE-2026-6686 and every CVE in our database. Create a free account — no credit card required.

Create Free Account
Plain-language analysis
Impact assessment and exploitation scenario in plain English
Attack graph visualization
Interactive attack path and kill chain mapping
Exploit details & PoC links
ExploitDB, Metasploit, GitHub PoCs with direct links
Nuclei scanner templates
Ready-to-use vulnerability scanner templates
Full remediation guide
Patch instructions, workarounds, and compliance impact
Interactive AI chat
Ask questions about this vulnerability in natural language
Related vulnerabilities
Semantically similar CVEs and attack patterns
REST API & MCP access
Integrate vulnerability data into your workflows