How severe is CVE-2026-6686?

CVE-2026-6686 has a CVSS 3.x base score of 4.6, rated medium severity. It is exploitable over physical access with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity none, and availability none.

Is CVE-2026-6686 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (7th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-6686?

CVE-2026-6686 affects Elm-chan Fatfs. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-6686?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2026-6686 published?

CVE-2026-6686 was published on 2026-07-01 and last updated on 2026-07-02.

CVE-2026-6686

CVE-2026-6686 is a medium-severity vulnerability in Elm-chan Fatfs with a CVSS 3.x base score of 4.6. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-908.

Key facts

Severity: Medium (CVSS 3.x base score 4.6)
EPSS exploit prediction: 0% (7th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-908
Affected product: Elm-chan Fatfs
Published: 2026-07-01
Last modified: 2026-07-02

Description

FatFs R0.16 and earlier contains an uninitialized cluster exposure when f_lseek() extends files beyond EOF without zero-filling newly allocated clusters. This maps to CWE-908 (Use of Uninitialized Resource). Estimated CVSS v3.1 vector: CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N (4.6, Medium). The estimated CISA SSVC vectors are Exploitation: PoC, Technical Impact: Partial.

Frequently asked questions

What is CVE-2026-6686?: FatFs R0.16 and earlier contains an uninitialized cluster exposure when f_lseek() extends files beyond EOF without zero-filling newly allocated clusters. This maps to CWE-908 (Use of Uninitialized Resource). Estimated CVSS v3.1 vector: CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N (4.6, Medium). The estimated CISA SSVC vectors are Exploitation: PoC, Technical Impact: Partial.
How severe is CVE-2026-6686?: CVE-2026-6686 has a CVSS 3.x base score of 4.6, rated medium severity. It is exploitable over physical access with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity none, and availability none.
Is CVE-2026-6686 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (7th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-6686?: CVE-2026-6686 affects Elm-chan Fatfs. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-6686?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2026-6686 published?: CVE-2026-6686 was published on 2026-07-01 and last updated on 2026-07-02.

References

Affected products (1)

cpe:2.3:a:elm-chan:fatfs:*:*:*:*:*:*:*:*

More vulnerabilities in Elm-chan Fatfs

CVE-2026-6688 — High (CVSS 7.6): FatFs R0.16 and earlier contains a downstream-caller vulnerability pattern associated with FatFs long filename…
CVE-2026-6687 — High (CVSS 7.6): FatFs R0.16 and earlier contains a stack overflow bug in f_getlabel() because exFAT label length (XDIR_NumLabel) is…
CVE-2026-6682 — High (CVSS 7.6): In FatFS R0.16 and earlier contains a FAT32 integer overflow bug in mount_volume() where fasize *= fs->n_fats can wrap,…
CVE-2026-6685 — Medium (CVSS 6.1): FatFs R0.16 and earlier exhibits a stale dirty-cache skip via unsigned-subtraction wrap in f_read() / f_write()…
CVE-2026-6684 — Medium (CVSS 4.6): FatFs prior to R0.16 that use GPT scanning with 'FF_LBA64 = 1' contains an issue where an unbounded loop count derived…
CVE-2026-6683 — Medium (CVSS 4.6): FatFs R0.16 and earlier contains a divide-by-zero in exFAT sync logic bug when crafted metadata causes n_fatent - 2 to…

All CVEs affecting Elm-chan Fatfs →

Other CWE-908 (Use of Uninitialized Resource) vulnerabilities

CVE-2025-1942 — Critical (CVSS 9.8): When String.toUpperCase() caused a string to get longer it was possible for uninitialized memory to be incorporated…
CVE-2024-47540 — Critical (CVSS 9.8): GStreamer is a library for constructing graphs of media-handling components. An uninitialized stack variable…
CVE-2024-32611 — Critical (CVSS 9.8): HDF5 Library through 1.14.3 may use an uninitialized value in H5A__attr_release_table in H5Aint.c.
CVE-2023-24941 — Critical (CVSS 9.8): Windows Network File System Remote Code Execution Vulnerability
CVE-2022-26437 — Critical (CVSS 9.8): In httpclient, there is a possible out of bounds write due to uninitialized data. This could lead to remote escalation…
CVE-2021-45703 — Critical (CVSS 9.8): An issue was discovered in the tectonic_xdv crate before 0.1.12 for Rust. XdvParser::<T>::process may read from…

Browse all CWE-908 (Use of Uninitialized Resource) vulnerabilities →