CVE-2026-6688
FatFs Buffer Overflow via Unbounded LFN Filename Copy
Description
FatFs R0.16 and earlier contains a downstream-caller vulnerability pattern associated with FatFs long filename handling. With LFN enabled, fno.fname can be up to 255 characters; many callers copy it into short fixed buffers without bounds checks, causing overflow. This maps to CWE-120 (Buffer Copy without Checking Size of Input). Estimated CVSS v3.1 vector: CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H (7.6, High). The estimated CISA SSVC vectors are Exploitation: PoC, Technical Impact: Total.
INFO
Published Date :
July 1, 2026, 3:17 p.m.
Last Modified :
July 2, 2026, 2:38 p.m.
Remotely Exploit :
No
Source :
44488dab-36db-4358-99f9-bc116477f914
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | |||||
| CVSS 3.1 | HIGH | 44488dab-36db-4358-99f9-bc116477f914 |
Solution
- Update FatFs to a version that fixes long filename handling.
- Ensure buffer copies include bounds checks.
- Review and sanitize all filename inputs.
- Recompile the application with the updated FatFs library.
Public PoC/Exploit Available at Github
CVE-2026-6688 has a 1 public
PoC/Exploit available at Github.
Go to the Public Exploits tab to see the list.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-6688.
| URL | Resource |
|---|---|
| https://elm-chan.org/fsw/ff/ | Product |
| https://github.com/runZeroInc/vulns-2026-fatfs-chance | Third Party Advisory Exploit |
| https://www.runzero.com/advisories/fatfs-long-fn-of-downstream-cve-2026-6688/ | Third Party Advisory |
| https://www.runzero.com/blog/fatfs-bugs/ | Third Party Advisory Exploit |
| https://github.com/runZeroInc/vulns-2026-fatfs-chance | Third Party Advisory Exploit |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-6688 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-6688
weaknesses.
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).
None
CSS HTML C Dockerfile CMake Shell Python Go Makefile
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-6688 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
The following table lists the changes that have been made to the
CVE-2026-6688 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.
-
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-long-fn-of-downstream-cve-2026-6688/ 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-2026-6688', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'poc'}, {'automatable': 'no'}, {'technicalImpact': 'total'}], 'version': '2.0.3', 'timestamp': '2026-07-01T15:06:55.618764Z'} -
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 contains a downstream-caller vulnerability pattern associated with FatFs long filename handling. With LFN enabled, fno.fname can be up to 255 characters; many callers copy it into short fixed buffers without bounds checks, causing overflow. This maps to CWE-120 (Buffer Copy without Checking Size of Input). Estimated CVSS v3.1 vector: CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H (7.6, High). The estimated CISA SSVC vectors are Exploitation: PoC, Technical Impact: Total. Added CVSS V3.1 AV:P/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H Added CWE CWE-120 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-long-fn-of-downstream-cve-2026-6688/ Added Reference https://www.runzero.com/blog/fatfs-bugs/