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Vulnerability record · CVE-2026-6684 · published 1 July 2026

CVE-2026-6684: Elm-chan fatfs vulnerability

Elm Chan · Fatfs

FatFs 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_PtNum, enabling extremely long or effectively infinite mount-time scans. This maps to CWE-835 (Loop with Unreachable Exit Condition). Estimated CVSS v3.1 vector: CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H (4.6, Medium). The estimated CISA SSVC vectors are Exploitation: PoC, Technical Impact: Partial.

4.6 CVSS 3.1 Medium EPSS 0.31% · top 79.0% CWE-835 · CWE-835
4.6CVSS 3.1 base score
0.31%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

FatFs 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_PtNum, enabling extremely long or effectively infinite mount-time scans. This maps to CWE-835 (Loop with Unreachable Exit Condition). Estimated CVSS v3.1 vector: CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H (4.6, Medium). The estimated CISA SSVC vectors are Exploitation: PoC, Technical Impact: Partial.

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

Affected products

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

References

LinkTags
https://elm-chan.org/fsw/ff/ Product
https://github.com/runZeroInc/vulns-2026-fatfs-chance Third Party AdvisoryExploit
https://www.runzero.com/advisories/fatfs-gpt-scan-loop-dos-cve-2026-6684/ Third Party Advisory
https://www.runzero.com/blog/fatfs-bugs/ Third Party AdvisoryExploit
https://github.com/runZeroInc/vulns-2026-fatfs-chance Third Party AdvisoryExploit

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Related vulnerabilities

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

7.6CVE-2026-6688Elm-chan fatfs classic buffer overflow vulnerabilityFatFs R0.16 and earlier contains a downstream-caller vulnerability pattern associated with FatFs long filename handling. With LFN enabled, fno.fname …EPSS 0.32%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%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%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%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%8.6CVE-2024-20353Cisco ASA and FTD web server HTTP header parsing DoSCisco ASA and FTD management and VPN web servers fail to fully check errors when parsing an HTTP header, so a crafted request can crash and reload th…KEVEPSS 71%analysed

Source: NIST National Vulnerability Database (record CVE-2026-6684), CISA KEV, FIRST EPSS (scores of 2026-09-28). This page is refreshed as NVD updates the record.