HOMEVULNERABILITIESCVE-2026-6686
MEDIUM

CVE-2026-6686

CWE-908Published: July 1, 2026· Updated: Jul 2, 2026

4.6
CVSS v3.1
EPSS:0.16%probability of exploitation in 30 daysPercentile:5.9th

Official 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.

NVD Source

Technical Analysis

CVE-2026-6686 requires local access, meaning attackers must already have a foothold on the target system.

The vulnerability requires no privileges and no user interaction, making it a prime target for automated exploitation campaigns and worm-like propagation.

A successful exploit results in complete confidentiality breach (data exposure), with a CVSS base score of 4.6.

CVSS v3.1 Vector Breakdown

Exploitability
Attack VectorPhysical
Attack ComplexityLow
Privileges Req.None
User InteractionNone
ScopeUnchanged
Impact
ConfidentialityHigh
IntegrityNone
AvailabilityNone
CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

Affected Vendors & Products

elm-chan1 product
fatfs
Source: NVD CPE · 1 total CPE entries

Exploit & PoC Resources

NO KNOWN EXPLOITNo public exploit confirmed at this time
Exploit-DB
Offensive Security exploit database
GitHub PoC Search
Community PoC repositories
Rapid7 / Metasploit
Metasploit module search
PacketStorm
Security advisories & exploits
NVD Detail
Official NIST entry
MITRE CVE
CVE Program entry
External links open in a new tab. Always verify in a controlled environment before use.

Official Patches & Advisories

ADVISORYhttps://github.com/runZeroInc/vulns-2026-fatfs-chance
ADVISORYhttps://www.runzero.com/advisories/fatfs-uninit-cluster-exposure-cve-2026-6686/
ADVISORYhttps://www.runzero.com/blog/fatfs-bugs/
ADVISORYhttps://github.com/runZeroInc/vulns-2026-fatfs-chance

All References (5)

→
https://elm-chan.org/fsw/ff/Product
→
https://github.com/runZeroInc/vulns-2026-fatfs-chanceThird Party Advisory · Exploit
→
https://www.runzero.com/advisories/fatfs-uninit-cluster-exposure-cve-2026-6686/Third Party Advisory
→
https://www.runzero.com/blog/fatfs-bugs/Third Party Advisory · Exploit
→
https://github.com/runZeroInc/vulns-2026-fatfs-chanceThird Party Advisory · Exploit

Quick Facts

CVE IDCVE-2026-6686
CVSS Score4.6 / 10
SeverityMEDIUM
WeaknessCWE-908
CISA KEVNo
EPSS (30d)0.16%
Affected1 vendor
PublishedJul 1, 2026

Related CVEs (CWE-908)

CVE-2026-2044
7.8
CVE-2026-34543
7.5
CVE-2026-45736
7.5
CVE-2026-3497
6.9
CVE-2025-48513
6.9
CVE-2026-58051
6.5

Recommended Actions

  • →Apply vendor patches immediately
  • →Monitor CVE-2026-6686 in threat intel feeds
  • →Review IDS/IPS signatures for exploitation attempts
Data sourced from NVD (NIST), CISA KEV, and EPSS (FIRST). Analysis generated by CTIWATCH.COM. CVE data is provided under the NVD usage policy.
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