Vulnerability record · CVE-2026-6688 · published 1 July 2026

CVE-2026-6688: Elm-chan fatfs classic buffer overflow vulnerability

Elm Chan · Fatfs

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.

7.6 CVSS 3.1 High EPSS 0.32% · top 77.3% CWE-120 · Classic buffer overflow

7.6CVSS 3.1 base score

0.32%EPSS exploitation probability, 30 days

NoNot in CISA KEV

1Affected product versions listed by NVD

5References, 3 tagged exploit

2 Jul 2026Last modified by NVD

Description

CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

Fatfs Elm Chan

References

Link	Tags
https://elm-chan.org/fsw/ff/	Product
https://github.com/runZeroInc/vulns-2026-fatfs-chance	Third Party AdvisoryExploit
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 AdvisoryExploit
https://github.com/runZeroInc/vulns-2026-fatfs-chance	Third Party AdvisoryExploit

Track CVE-2026-6688 inside VULONE

Watch it alongside the ransomware crews, C2 infrastructure and forum chatter that reference it, query it through the API and pull it into your SIEM over TAXII.

Start free Open in platform

Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

7.6CVE-2026-6682Elm-chan fatfs integer overflow vulnerabilityIn FatFS R0.16 and earlier contains a FAT32 integer overflow bug in mount_volume() where fasize *= fs->n_fats can wrap, leading to attacker-controlle…EPSS 0.32%1 Jul 2026 7.6CVE-2026-6687Elm-chan fatfs stack-based buffer overflow vulnerabilityFatFs R0.16 and earlier contains a stack overflow bug in f_getlabel() because exFAT label length (XDIR_NumLabel) is trusted without enforcing spec ma…EPSS 0.35%1 Jul 2026 4.6CVE-2026-6683Elm-chan fatfs divide by zero vulnerabilityFatFs R0.16 and earlier contains a divide-by-zero in exFAT sync logic bug when crafted metadata causes n_fatent - 2 to be zero during write/sync oper…EPSS 0.31%1 Jul 2026 4.6CVE-2026-6684Elm-chan fatfs vulnerabilityFatFs prior to R0.16 that use GPT scanning with 'FF_LBA64 = 1' contains an issue where an unbounded loop count derived from GPT header field GPTH_PtN…EPSS 0.31%1 Jul 2026 4.6CVE-2026-6686Elm-chan fatfs use of uninitialized resource vulnerabilityFatFs R0.16 and earlier contains an uninitialized cluster exposure when f_lseek() extends files beyond EOF without zero-filling newly allocated clust…EPSS 0.26%1 Jul 2026 5.5CVE-2025-43520Apple OS kernel memory corruption via malicious appA memory corruption flaw (classic buffer overflow) in Apple's kernel was fixed across iOS, iPadOS, macOS, tvOS, visionOS and watchOS. A malicious app…KEVEPSS 0.43%analysed12 Dec 2025 8.8CVE-2025-31277Apple WebKit memory corruption via malicious web contentApple WebKit fails to handle memory correctly when processing crafted web content, leading to memory corruption across Safari, iOS, iPadOS, macOS, tv…KEVEPSS 1.6%analysed30 Jul 2025 9.8CVE-2022-37055D-Link Go-RT-AC750 router buffer overflow in cgibin hnap_mainD-Link Go-RT-AC750 firmware revisions A v101b03 and B v200b02 contain a classic buffer overflow reachable through the cgibin hnap_main handler. The f…KEVEPSS 56%analysed28 Aug 2022

Source: NIST National Vulnerability Database (record CVE-2026-6688), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.