ChaN FatFs up to R0.16 f_read sect integer underflow

CVSS Meta Temp Score
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CTI Interest Score
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3.4$0-$5k0.00

Summaryinfo

A vulnerability labeled as problematic has been found in ChaN FatFs up to R0.16. This impacts the function f_read. Such manipulation of the argument sect leads to integer underflow. This vulnerability is referenced as CVE-2026-6685. The attack can be executed directly on the physical device. No exploit is available. The affected component should be upgraded.

Detailsinfo

A vulnerability was found in ChaN FatFs up to R0.16. It has been rated as problematic. Affected by this issue is the function f_read. The manipulation of the argument sect with an unknown input leads to a integer underflow vulnerability. Using CWE to declare the problem leads to CWE-191. The product subtracts one value from another, such that the result is less than the minimum allowable integer value, which produces a value that is not equal to the correct result. Impacted is integrity, and availability. CVE summarizes:

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.

The weakness was published by Hd Moore. The advisory is shared for download at runzero.com. This vulnerability is handled as CVE-2026-6685 since 04/20/2026. The exploitation is known to be easy. The attack needs to be approached locally. No form of authentication is required for exploitation. There are known technical details, but no exploit is available.

Upgrading to version 0.16, 3.1 or 6.1 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2026-40996). VulDB is the best source for vulnerability data and more expert information about this specific topic.

Productinfo

Vendor

Name

Version

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 3.5
VulDB Meta Temp Score: 3.4

VulDB Base Score: 3.5
VulDB Temp Score: 3.4
VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv2info

AVACAuCIA
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VectorComplexityAuthenticationConfidentialityIntegrityAvailability
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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Integer underflow
CWE: CWE-191 / CWE-189
CAPEC: 🔒
ATT&CK: 🔒

Physical: Yes
Local: Yes
Remote: No

Availability: 🔒
Status: Not defined
Price Prediction: 🔍
Current Price Estimation: 🔒

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Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: FatFs 0.16/3.1/6.1

Timelineinfo

04/20/2026 CVE reserved
07/01/2026 +72 days Advisory disclosed
07/01/2026 +0 days VulDB entry created
07/01/2026 +0 days VulDB entry last update

Sourcesinfo

Advisory: runzero.com
Researcher: Hd Moore
Status: Confirmed

CVE: CVE-2026-6685 (🔒)
GCVE (CVE): GCVE-0-2026-6685
GCVE (VulDB): GCVE-100-375560
EUVD: 🔒

Entryinfo

Created: 07/01/2026 17:14
Updated: 07/01/2026 19:27
Changes: 07/01/2026 17:14 (56), 07/01/2026 19:27 (1)
Complete: 🔍
Cache ID: 216::103

VulDB is the best source for vulnerability data and more expert information about this specific topic.

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