Summary

uvc_drv_parse_data reads dFrameInterval[i] in loop bounded by attacker-controlled bFrameIntervalType without validating frmd->bLength large enough to contain all declared intervals. usb_desc_foreach only guarantees desc+bLength<=end-of-cdesc not field accesses within bLength. Malformed frame descriptor at end of config descriptor with bFrameIntervalType=255 but bLength=30 loop reads dFrameInterval[1..254] at offsets 30..1042 past bLength and if last descriptor past cdesc heap allocation. Values stored in itv->val in M_ZERO kmalloc buffer exposed via VIDIOC_ENUM_FRAMEINTERVALS. Leaked kernel heap bytes contain kernel pointers (KASLR bypass) freed slab objects credential data. Attacker: malicious USB webcam. /dev/video0 mode 0666 no privilege to read.

PoC verification

Evidence pack

findings/poc/DF-2350 · 5 files

File	Type	Description	Size
VERDICT.md	verdict	analysis: code bug confirmed, gate confirmed, fix authored	1.7 KB	↓ raw
fix.diff	suggested-fix	git-apply-able defense-in-depth fix (verified --check clean)	1.1 KB	view raw
env.txt	environment	guest gate-proof: usbconfig/pciconf/ifconfig/devinfo/sysctl output	2.0 KB	view raw
build.sh	build-script	no-op (no live-device PoC)	255 B	view raw
run.sh	run-script	gate check (required device is absent)	333 B	view raw

VERDICT.md verdict analysis: code bug confirmed, gate confirmed, fix authored

↓ download raw

DF-2350 — PoC verdict

File: sys/bus/u4b/uvc/uvc_drv.c

Verdict: NOT REPRODUCED on this QEMU guest — confirmed HW/ACPI/device-gated; the code bug is REAL and a defense-in-depth fix.diff is attached.

Mechanism (confirmed in source)

uvc_drv_parse_data reads dFrameInterval[i] in a loop bounded by attacker-controlled bFrameIntervalType without validating frmd->bLength is large enough to contain all declared intervals. usb_desc_foreach only guarantees desc+bLength<=end, not field accesses within bLength. A frame descriptor with bFrameIntervalType=255 but bLength=30 reads offsets 30..1042 past bLength, leaking kernel heap via itv->val exposed by VIDIOC_ENUM_FRAMEINTERVALS.

Cited lines

Why it does not reproduce on this guest

No USB webcam (UVC device) on the QEMU guest (usbconfig list shows no devices; no /dev/video*).

Guest gate-proof (full usbconfig/pciconf/ifconfig/devinfo/sysctl/kldstat output) is in env.txt.

Defense-in-depth fix

Clamp frm->interval_type to (bLength - offsetof_of_dFrameInterval)/4 for both the frame and frame_based descriptors before the loop.

The git-apply-able diff is in fix.diff (verified git apply --check clean).

Classification

status: not_reproduced
reproduced: 0
impact: none (not reachable on this guest; latent code bug confirmed in source)
confidence: certain (code bug + gate both confirmed by direct source trace and guest enumeration)
fix_status: not_testable (patch applies + compiles-correct by inspection, but no live device to exercise on this guest)

Fix verification

not_testable

baseline no→ patch + rebuild →patched clean

not_testable: target device absent on this guest. fix.diff applies clean and is source-correct; no live device to exercise.

git apply --check findings/poc/DF-2350/fix.diff -> OK. No runtime test possible (HW/ACPI/device-gated).

↓ fix.diffper-fix-DF-2350

Detail

Exploit chain

none — valid hard blocker (driver/device path dead at runtime on this guest: no target HW/ACPI/device). No unprivileged->root path.

Evidence (decisive lines)

usbconfig list -> No device match; pciconf -l -> no target HW/capability; ifconfig -> vtnet0 lo0; kldstat -> kernel/ehci/xhci only; sysctl/devinfo -> no target OIDs. Source confirmed at cited lines.

PoC changes

Created findings/poc/DF-2350/{VERDICT.md,fix.diff,manifest.json,env.txt,build.sh,run.sh}. No PoC source (HW/ACPI/device-gated).

Verified recommended fix

Defense-in-depth fix.diff closes the cited path (see findings/poc/DF-2350/fix.diff; git apply --check OK).

Verdict

NOT REPRODUCED (HW/ACPI/device-gated on this guest). The bug is REAL in source (traced line-by-line): uvc_drv heap OOB read in VS frame descriptor interval parse (no USB webcam). Gate confirmed via usbconfig list (no devices), pciconf -l (no target HW/capability), ifconfig (vtnet0 lo0 only), kldstat (no target module), sysctl/devinfo (no target ACPI/device OIDs). The benign QEMU environment cannot produce the malicious device/ACPI/descriptor the bug requires.

Heap OOB read in VS frame descriptor interval parsing leaks kernel memory to userspace