6.1
MEDIUM
CVSS 3.1
CVE-2026-6685
FatFs Integer Underflow in Dirty-Sector Cache Flush
Overview
Description
Rejected reason: This CVE ID has been rejected or withdrawn by its CVE Numbering Authority following a notification that the vulnerability determination was made in error. After review, the CNA confirmed the erroneous finding. Thanks to David Brown for reaching out about this issue.
Details
INFO
Published Date :
July 1, 2026, 3:17 p.m.
Last Modified :
July 16, 2026, 9:17 p.m.
Remotely Exploit :
No
Source :
44488dab-36db-4358-99f9-bc116477f914
Scoring
CVSS Scores
The Common Vulnerability Scoring System is a standardized framework
for assessing the severity of vulnerabilities in software and systems.
We collect and displays CVSS scores from various sources for each CVE.
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | |||||
| CVSS 3.1 | MEDIUM | 44488dab-36db-4358-99f9-bc116477f914 |
Solution
Update FatFs to a version that addresses integer underflow issues in read/write operations.
- Update FatFs to a non-vulnerable version.
- Apply relevant patches for FatFs R0.16.
- Review filesystem access patterns.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-6685 vulnerability anywhere in the article.
-
The Hacker News
Unpatched Flaws Disclosed in Filesystem Bundled Into Millions of Embedded Devices
Security firm runZero has disclosed seven vulnerabilities in FatFs, a small filesystem library that lets a device read and write the FAT and exFAT formats used on USB drives and SD cards. The flaws ma ... Read more
Published Date:
Jul 03, 2026 (4 weeks, 2 days ago)
The following table lists the changes that have been made to the
CVE-2026-6685 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
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CVE Rejected by 44488dab-36db-4358-99f9-bc116477f914
Jul. 16, 2026
Action Type Old Value New Value -
CVE Modified by 44488dab-36db-4358-99f9-bc116477f914
Jul. 16, 2026
Action Type Old Value New Value Removed Affected [{'vendor': 'ChaN', 'product': 'FatFs', 'versions': [{'status': 'affected', 'version': '0', 'versionType': 'custom', 'lessThanOrEqual': 'R0.16'}], 'defaultStatus': 'unaffected'}] Removed SSVC {'id': 'CVE-2026-6685', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'poc'}, {'automatable': 'no'}, {'technicalImpact': 'partial'}], 'version': '2.0.3', 'timestamp': '2026-07-01T15:26:17.001634Z'} Removed Tag runZero: disputed Changed Description FatFs R0.16 and earlier exhibits a stale dirty-cache skip via unsigned-subtraction wrap in f_read() / f_write() (fp->sect - sect < cc) during interleaved read/write on fragmented filesystems. This maps to CWE-191 (Integer Underflow). Estimated CVSS v3.1 vector: CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H (6.1, Medium). The estimated CISA SSVC vectors are Exploitation: PoC, Technical Impact: Total. Note that this issue has been disputed by the Supplier. It will be rejected shortly. Rejected reason: This CVE ID has been rejected or withdrawn by its CVE Numbering Authority following a notification that the vulnerability determination was made in error. After review, the CNA confirmed the erroneous finding. Thanks to David Brown for reaching out about this issue. Removed CVSS V3.1 runZero: AV:P/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H Removed CWE runZero: CWE-191 Removed CPE Configuration OR *cpe:2.3:a:elm-chan:fatfs:*:*:*:*:*:*:*:* versions up to (including) r0.16 Removed Reference runZero: https://elm-chan.org/fsw/ff/ Removed Reference runZero: https://github.com/runZeroInc/vulns-2026-fatfs-chance Removed Reference runZero: https://www.runzero.com/advisories/fatfs-unsigned-sub-wrap-cve-2026-6685/ Removed Reference runZero: https://www.runzero.com/blog/fatfs-bugs/ Removed Reference CISA-ADP: https://github.com/runZeroInc/vulns-2026-fatfs-chance Removed Reference Type runZero: https://elm-chan.org/fsw/ff/ Types: Product Removed Reference Type runZero: https://github.com/runZeroInc/vulns-2026-fatfs-chance Types: Exploit, Third Party Advisory Removed Reference Type runZero: https://www.runzero.com/advisories/fatfs-unsigned-sub-wrap-cve-2026-6685/ Types: Third Party Advisory Removed Reference Type runZero: https://www.runzero.com/blog/fatfs-bugs/ Types: Exploit, Third Party Advisory Removed Reference Type CISA-ADP: https://github.com/runZeroInc/vulns-2026-fatfs-chance Types: Exploit, Third Party Advisory -
CVE Modified by 44488dab-36db-4358-99f9-bc116477f914
Jul. 16, 2026
Action Type Old Value New Value Added Tag disputed Changed Description FatFs R0.16 and earlier exhibits a stale dirty-cache skip via unsigned-subtraction wrap in f_read() / f_write() (fp->sect - sect < cc) during interleaved read/write on fragmented filesystems. This maps to CWE-191 (Integer Underflow). Estimated CVSS v3.1 vector: CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H (6.1, Medium). The estimated CISA SSVC vectors are Exploitation: PoC, Technical Impact: Total. FatFs R0.16 and earlier exhibits a stale dirty-cache skip via unsigned-subtraction wrap in f_read() / f_write() (fp->sect - sect < cc) during interleaved read/write on fragmented filesystems. This maps to CWE-191 (Integer Underflow). Estimated CVSS v3.1 vector: CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H (6.1, Medium). The estimated CISA SSVC vectors are Exploitation: PoC, Technical Impact: Total. Note that this issue has been disputed by the Supplier. It will be rejected shortly. -
Initial Analysis by [email protected]
Jul. 02, 2026
Action Type Old Value New Value Added CPE Configuration OR *cpe:2.3:a:elm-chan:fatfs:*:*:*:*:*:*:*:* versions up to (including) r0.16 Added Reference Type CISA-ADP: https://github.com/runZeroInc/vulns-2026-fatfs-chance Types: Exploit, Third Party Advisory Added Reference Type runZero: https://elm-chan.org/fsw/ff/ Types: Product Added Reference Type runZero: https://github.com/runZeroInc/vulns-2026-fatfs-chance Types: Exploit, Third Party Advisory Added Reference Type runZero: https://www.runzero.com/advisories/fatfs-unsigned-sub-wrap-cve-2026-6685/ Types: Third Party Advisory Added Reference Type runZero: https://www.runzero.com/blog/fatfs-bugs/ Types: Exploit, Third Party Advisory -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Jul. 01, 2026
Action Type Old Value New Value Added Reference https://github.com/runZeroInc/vulns-2026-fatfs-chance Added SSVC {'id': 'CVE-2026-6685', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'poc'}, {'automatable': 'no'}, {'technicalImpact': 'partial'}], 'version': '2.0.3', 'timestamp': '2026-07-01T15:26:17.001634Z'} -
New CVE Received by 44488dab-36db-4358-99f9-bc116477f914
Jul. 01, 2026
Action Type Old Value New Value Added Affected [{'vendor': 'ChaN', 'product': 'FatFs', 'versions': [{'status': 'affected', 'version': '0', 'versionType': 'custom', 'lessThanOrEqual': 'R0.16'}], 'defaultStatus': 'unaffected'}] Added Description FatFs R0.16 and earlier exhibits a stale dirty-cache skip via unsigned-subtraction wrap in f_read() / f_write() (fp->sect - sect < cc) during interleaved read/write on fragmented filesystems. This maps to CWE-191 (Integer Underflow). Estimated CVSS v3.1 vector: CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H (6.1, Medium). The estimated CISA SSVC vectors are Exploitation: PoC, Technical Impact: Total. Added CVSS V3.1 AV:P/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H Added CWE CWE-191 Added Reference https://elm-chan.org/fsw/ff/ Added Reference https://github.com/runZeroInc/vulns-2026-fatfs-chance Added Reference https://www.runzero.com/advisories/fatfs-unsigned-sub-wrap-cve-2026-6685/ Added Reference https://www.runzero.com/blog/fatfs-bugs/
EPSS is a daily estimate of the probability of exploitation activity
being observed over the next 30 days. Following chart shows the EPSS
score history of the vulnerability.