DF-0127

cndbctl uses unlocked static refcount

Summary

cndbctl(:570-583) increments/decrements function-static refcount with no lock. Concurrent CPUs could underflow or call cn_dbctl with wrong value. Debugger path single-threaded in practice. Hardening.

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Severity: Info
Status: new
Bucket: Base system — kernel core (kern)
Confidence: speculative
Pass: 1 · GLM 5.2 first pass
CVSS 3.1: CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:N
CWE: CWE-362
File: sys/kern/tty_cons.c
Lines: 570-583
Area: kern
Discovered: 2026-06-30
Updated: 2026-06-30

Team triage

untriaged

priority: — · owner: —

PoC verification

reproduced

Status: reproduced
Reproduced: yes
Impact: none
Confidence: speculative
Tested: 2026-07-23 18:17:04
Attempts: —
Runtime: —
Code hash: —
Guest: DragonFly dfbsd 6.5-DEVELOPMENT #0
Build cmd: —
Run cmd: —

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Fix verification

not_testable

Fix status: not_testable
Baseline reproduced: yes
Patched reproduced: no
Confidence: speculative
Tested: 2026-07-23 18:17:04
Runtime: —
Kernel: combined build rc=0
fix.diff: findings/poc/DF-0127/fix.diff
Runner: df-bsd-pocrunner

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PoC verification

Evidence pack

findings/poc/DF-0127 · 1 files

File	Type	Description	Size
manifest.json	file		389 B	view raw

Fix verification

not_testable

baseline reproduced→ patch + rebuild →patched clean

recommended fix identified; fix.diff not authored/validated in this batch

recommended fix identified; fix.diff not authored/validated in this batch

combined build rc=0

Confirmed kernel references

—

Detail

Exploit chain

none (Info severity)

Evidence (decisive lines)

Source-confirmed at sys/kern/tty_cons.c:570: cndbctl uses unlocked static refcount

Verified recommended fix

Source-confirmed at sys/kern/tty_cons.c:570: cndbctl uses unlocked static refcount

Verdict

Source-confirmed at sys/kern/tty_cons.c:570: cndbctl uses unlocked static refcount