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CVE-2026-6688— FatFs Buffer Overflow via Unbounded LFN Filename Copy

Quick assessment

Affected
ChaN FatFs
Exploitation
Public or AI PoC available; prioritize validation
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

ChaN FatFs是ChaN公司的一个为嵌入式系统设计的通用 FAT/exFAT 文件系统模块。 ChaN FatFs R0.16及之前版本存在缓冲区错误漏洞，该漏洞源于FatFs长文件名处理中存在下游调用者漏洞模式，启用LFN时，fno.fname最多可达255个字符，许多调用者将其复制到没有边界检查的短固定缓冲区中，导致缓冲区溢出。

CVSS 7.6 · High EPSS 0.32% · P23

Possible ATT&CK Techniques 1 AI

T1203 · Exploitation for Client Execution

Affected Version Matrix 1

VendorProduct Version RangeStatus
ChaN FatFs ≤ R0.16 affected
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I. Basic Information for CVE-2026-6688

Vulnerability Information
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Vulnerability Title
FatFs Buffer Overflow via Unbounded LFN Filename Copy
Source: CVE Program / CVE List V5
Vulnerability Description
FatFs R0.16 and earlier contains a downstream-caller vulnerability pattern associated with FatFs long filename handling. With LFN enabled, fno.fname can be up to 255 characters; many callers copy it into short fixed buffers without bounds checks, causing overflow. This maps to CWE-120 (Buffer Copy without Checking Size of Input). 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
未进行输入大小检查的缓冲区拷贝(传统缓冲区溢出)
Source: CVE Program / CVE List V5
Vulnerability Title
ChaN FatFs 缓冲区错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
ChaN FatFs是ChaN公司的一个为嵌入式系统设计的通用 FAT/exFAT 文件系统模块。 ChaN FatFs R0.16及之前版本存在缓冲区错误漏洞，该漏洞源于FatFs长文件名处理中存在下游调用者漏洞模式，启用LFN时，fno.fname最多可达255个字符，许多调用者将其复制到没有边界检查的短固定缓冲区中，导致缓冲区溢出。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
ChaN FatFs 0 ~ R0.16 -

II. Public POCs for CVE-2026-6688

# POC Description Source Link Shenlong Link
AI-Generated POC Premium
Qwen3.6-35B-A3B · 8464 chars
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Vulnerability reproduction recording (real sandbox build + trigger, exclusive)
In-depth vulnerability mechanism
Trigger conditions & impact
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III. Intelligence Information for CVE-2026-6688

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Vendor Advisories for CVE-2026-6688 (1)

Security Blog Posts for CVE-2026-6688 (1)

Vendor Pages for CVE-2026-6688 (1)

Other References for CVE-2026-6688 (1)

Same Patch Batch · ChaN · 2026-07-01 · 6 CVEs total

CVE-2026-6687 7.6 HIGH FatFs Stack Buffer Overflow via Uncapped exFAT Label Length
CVE-2026-6682 7.6 HIGH FatFs Integer Overflow in FAT32 Volume Mount
CVE-2026-6684 4.6 MEDIUM FatFs Infinite Loop in GPT Partition Scan
CVE-2026-6686 4.6 MEDIUM FatFs Use of Uninitialized Clusters After Seek Past EOF
CVE-2026-6683 4.6 MEDIUM FatFs Divide-by-Zero in exFAT Sync

IV. Related Vulnerabilities

Same product: FatFs
Same vendor: ChaN
Same weakness: CWE-120

V. Comments for CVE-2026-6688

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