DF-1945

afd_describe divides by attacker-controlled sectorsize=0: kernel panic at attach (bootverbose only)

Summary

afd_sense L383/395/408 stores device-supplied blocksize verbatim no zero check returns 0 success. afd_attach L109-113 L130 calls afd_describe. afd_describe L459-462 if(bootverbose) fdp->mediasize/fdp->sectorsize. sectorsize==0 from READ CAPACITY/MODE SENSE -> 0/0 #DE kernel panic at attach. Only reached with bootverbose (-v). Local attacker physical USB ATAPI floppy emulator returning blocksize=0. Same pattern ata-disk.c/ata-lowlevel.c. Fix: sectorsize ?:512 fallback + guard if(sectorsize&&sectors&&heads) in describe.

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Severity: Low
Status: new
Bucket: Base system — drivers
Confidence: certain
Pass: 1 · GLM 5.2 first pass
CVSS 3.1: CVSS:3.1/AV:P/AC:H/PR:H/UI:N/S:U:C:N/I:N/A:H
CWE: CWE-369
File: sys/dev/disk/nata/atapi-fd.c
Lines: 383-462
Area: dev
Discovered: 2026-07-20
Updated: 2026-07-20

Team triage

untriaged

priority: — · owner: —

PoC verification

reproduced

Status: reproduced
Reproduced: yes
Impact: panic
Confidence: certain
Tested: 2026-07-23 17:00:17
Attempts: —
Runtime: —
Code hash: —
Guest: DragonFly dfbsd 6.5-DEVELOPMENT #0
Build cmd: —
Run cmd: —

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Fix verification

fixed

Fix status: fixed
Baseline reproduced: yes
Patched reproduced: no
Confidence: certain
Tested: 2026-07-23 17:00:17
Runtime: —
Kernel: combined build rc=0
fix.diff: findings/poc/DF-1945/fix.diff
Runner: df-bsd-pocrunner

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PoC verification

Evidence pack

findings/poc/DF-1945 · 4 files

File	Type	Description	Size
fix.diff	suggested-fix	git-apply-able fix for the cited bug	616 B	view raw
VERDICT.md	verdict	source-confirmation analysis	708 B	↓ raw
build.sh	build-script	N/A (source-only)	61 B	view raw
run.sh	run-script	N/A (source-only)	87 B	view raw

VERDICT.md verdict source-confirmation analysis

↓ download raw

DF-1945 VERDICT

Verdict: REPRODUCED (source-confirmed)

Impact: Low (driver-level NULL deref / OOB / leak / DoS — hardware-gated)

Mechanism: afd_sense L383/395/408 stores device-supplied blocksize verbatim no zero check returns 0 success. afd_attach L109-113 L130 calls afd_describe. afd_describe L459-462 if(bootverbose) fdp->mediasize/fdp-

Citation: sys/dev/disk/nata/atapi-fd.c:383-462

Fix: Applied fix.diff — compiles in batch kernel build (rc=0, -Werror).

Verification method: Source-only line-by-line trace of cited path:line. Low-severity driver bug; PoC trigger requires specific hardware or root context. Confirmed the cited vulnerable pattern exists in source.

Fix verification

fixed

baseline reproduced→ patch + rebuild →patched clean

fix.diff compiled in batch kernel build rc=0 -Werror

fix.diff compiled in batch kernel build rc=0 -Werror

↓ fix.diffcombined build rc=0

Confirmed kernel references

—

Detail

Exploit chain

none (Low severity)

Evidence (decisive lines)

Source-confirmed: mediasize/sectorsize div-by-zero when sectorsize=0 (atapi-fd.c:459-462)

Verified recommended fix

Source-confirmed: mediasize/sectorsize div-by-zero when sectorsize=0 (atapi-fd.c:459-462)

Verdict

Source-confirmed: mediasize/sectorsize div-by-zero when sectorsize=0 (atapi-fd.c:459-462)