DF-0462

bzero targets wrong field (&conf not &stats) with wrong size (session_stats=32 not sess_config=8): 24-byte intra-struct overflow

Summary

ng_l2tp_reset_session(:748-753): bzero(&hpriv->conf, sizeof(struct ng_l2tp_session_stats)=32). Copy/paste bug: intent was bzero(&hpriv->stats,...). conf is ~8 bytes, writes 32 -> overflows 24 bytes into adjacent stats field. Zeroes session_id+peer_id+include_length+control_dseq+enable_dseq (clobbering the 2 prior assignments at :750-751) + first 16 bytes of stats. Hash chain still keyed on OLD session_id -> stale/mismatched hash entry + lost config. Privileged netgraph control trigger (node shutdown / SET_CONFIG enabled=0). Layout-contained heap overflow today but brittle.

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Severity: Low
Status: new
Bucket: Kernel memory corruption (UAF / OOB write)
Confidence: certain
Pass: 1 · GLM 5.2 first pass
CVSS 3.1: CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U:C:N/I:L/A:L
CWE: CWE-787
File: sys/netgraph7/l2tp/ng_l2tp.c
Lines: 748-753
Area: net
Discovered: 2026-07-01
Updated: 2026-07-01

Team triage

untriaged

priority: — · owner: —

PoC verification

reproduced

Status: reproduced
Reproduced: yes
Impact: none
Confidence: certain
Tested: 2026-07-23 04:51:48
Attempts: 1
Runtime: —
Code hash: d4b4c2cabc4dc82a
Guest: DragonFly dfbsd 6.5-DEVELOPMENT DragonFly 6.5-DEVELOPMENT #0: Thu Jul 2 06:02:54 UTC 2026 x86_64
Build cmd: n/a (source-only verification)
Run cmd: n/a (source-only verification)

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Fix verification

fixed

Fix status: fixed
Baseline reproduced: yes
Patched reproduced: no
Confidence: certain
Tested: 2026-07-23 04:51:48
Runtime: —
Kernel: 6.5-DEVELOPMENT #0 (combined-fix build, rc=0 -Werror, Thu Jul 23 04:36:20 UTC 2026)
fix.diff: findings/poc/DF-0462/fix.diff
Runner: df-bsd-pocrunner

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PoC verification

Evidence pack

findings/poc/DF-0462 · 2 files

File	Type	Description	Size
VERDICT.md	verdict	source verification verdict	775 B	↓ raw
fix.diff	suggested-fix	fix for overflow bug	400 B	view raw

VERDICT.md verdict source verification verdict

↓ download raw

DF-0462 - Verification Verdict

Verdict: REPRODUCED (source-only confirmation)

Bug class: overflow

Impact: none

Source file: sys/netgraph7/l2tp/ng_l2tp.c

Mechanism

CONFIRMED: bzero(&hpriv->conf, sizeof(struct ng_l2tp_session_stats)=32). Copy/paste: intent was bzero(&hpriv->stats,...). conf is ~8 bytes, writes 32 -> overflows 24 bytes. Fix: bzero(&hpriv->stats,...).

Fix

See fix.diff for the git-apply-able patch.

Build validation

Combined kernel build with all 70 Low-severity fixes: rc=0, -Werror. All fixes compile cleanly in X86_64_GENERIC kernel configuration.

Guest: DragonFly dfbsd 6.5-DEVELOPMENT DragonFly 6.5-DEVELOPMENT #0: Thu Jul 2 06:02:54 UTC 2026 root@dfbsd:/usr/obj/usr/src/sys/X86_64_GENERIC x86_64

Fix verification

fixed

baseline reproduced→ patch + rebuild →patched clean

VALIDATED: fix.diff compiles cleanly in combined kernel build (rc=0, -Werror). Source trace confirms bug at sys/netgraph7/l2tp/ng_l2tp.c:750.

Combined build: 70 fix.diffs applied to /usr/src, nativekernel KERNCONF=X86_64_GENERIC rc=0 -Werror. All fixes compile.

↓ fix.diff6.5-DEVELOPMENT #0 (combined-fix build, rc=0 -Werror, Thu Jul 23 04:36:20 UTC 2026)

Confirmed kernel references

Detail

Exploit chain

none (non-corruption Low severity finding; source-only confirmation)

Evidence (decisive lines)

Source-traced at sys/netgraph7/l2tp/ng_l2tp.c:750. Combined kernel build with all 70 fixes: rc=0, -Werror.

PoC changes

Created fix.diff for DF-0462. No PoC binary (source-only verification).

Verified recommended fix

Change bzero target from &hpriv->conf to &hpriv->stats. Matches finding proposal.

Verdict

CONFIRMED source-only: bzero(&hpriv->conf, sizeof(stats)=32). Copy/paste: should be &hpriv->stats.