CVE-2026-6687: FatFs Stack Buffer Overflow via Uncapped exFAT Label Length

Severity: high (CVSS 7.6 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2026-07-01 · updated 2026-10-25
Weakness: CWE-121

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.

Affected products

ChaN FatFs: through r0.16

References

https://elm-chan.org/fsw/ff/
https://github.com/runZeroInc/vulns-2026-fatfs-chance
https://www.runzero.com/advisories/fatfs-exfat-label-len-of-cve-2026-6687/
https://www.runzero.com/blog/fatfs-bugs/
https://github.com/runZeroInc/vulns-2026-fatfs-chance

Get alerted when CVE-2026-6687 or the next vulnerability affects your stack