Quick answers
- Is CVE-2026-6685 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-6685 being exploited in the wild.
- How severe is CVE-2026-6685?
- Medium severity, with a CVSS score of 6.1, published 1 July 2026.
- Which products and versions are affected?
- ChaN FatFs R0.16 and earlier.
- Is there a fix for CVE-2026-6685?
- No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
- How is CVE-2026-6685 attacked?
- It is attacked with physical access, in a software library.
- Am I affected by CVE-2026-6685?
- Check whether you run ChaN FatFs at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.
Technical details
An integer underflow (CWE-191) exists in the dirty-cache handling logic of f_read() and f_write(). The vulnerability occurs when the cached sector (fp->sect) is numerically lower than the current sector (sect), which is common on fragmented volumes. The subtraction 'fp->sect - sect' wraps to a large unsigned value, which may still satisfy the ' < cc' boundary check if the transfer count is large. This causes a memcpy to execute with an out-of-bounds offset, leading to stale data being written to the buffer or memory corruption. This is exploitable via physical access using fragmented media or by inducing fragmentation over time on long-lived devices.
Affected products
- ChaN FatFs R0.16 and earlier
Timeline
- 2026-06-30: advisory: runZero published detailed advisory
- 2026-07-01: disclosed: CVE published to NVD