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Vulnerability record · CVE-2026-6687 · published 1 July 2026

CVE-2026-6687: Elm-chan fatfs stack-based buffer overflow vulnerability

Elm Chan · Fatfs

FatFs R0.16 and earlier contains a stack overflow bug in f_getlabel() because exFAT label length (XDIR_NumLabel) is trusted without enforcing spec maximums. This maps to CWE-121 (Stack-based Buffer Overflow). 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 0.35% · top 74.2% CWE-121 · Stack-based buffer overflow
7.6CVSS 3.1 base score
0.35%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 R0.16 and earlier contains a stack overflow bug in f_getlabel() because exFAT label length (XDIR_NumLabel) is trusted without enforcing spec maximums. This maps to CWE-121 (Stack-based Buffer Overflow). 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.

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.

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-exfat-label-len-of-cve-2026-6687/ 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%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-2026-6684Elm-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%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%8.8CVE-2026-7273Zyxel gs1900-8 firmware stack-based buffer overflow vulnerabilityA stack-based buffer overflow vulnerability in the CGI program of Zyxel GS1900-48HPv2 firmware versions through 2.90(ABTQ.1)C0 could allow a LAN-base…KEVEPSS 2.5%8.1CVE-2021-27137DD-WRT UPnP M-SEARCH stack buffer overflowDD-WRT before 45724 contains an unsafe strcpy in the UPnP SSDP handling code (ssdp_msearch), reachable via an M-SEARCH request, that overflows a fixe…KEVEPSS 4.0%analysed9.3CVE-2025-53521F5 BIG-IP APM stack buffer overflow allows remote code executionA stack-based buffer overflow (CWE-121) exists in F5 BIG-IP Access Policy Manager when an APM access policy is configured on a virtual server. Specif…KEVEPSS 2.3%analysed

Source: NIST National Vulnerability Database (record CVE-2026-6687), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.