DF-0387

No MRRU enforcement on MP fragment reassembly: peer can assemble oversized PDUs beyond negotiated MRRU

Summary

ng_ppp_get_packet(:1203-1234) reassembles first..last fragments accumulating m_pkthdr.len but never compares against negotiated MRRU(priv->conf.mrru). TX path enforces mru(:968-972) but RX does not. Peer sends valid fragments each within link MRU reassembling up to ~128*1500=192KiB >> MRRU. Bounded by MP_MAX_QUEUE_LEN=128 cap, int len cannot overflow. RFC 1990 non-compliance + resource amplification. Downstream consumer normally drops/truncates.

Discussion (0)

No comments yet.

Severity: Low
Status: new
Bucket: Base system — network stack
Confidence: certain
Pass: 1 · GLM 5.2 first pass
CVSS 3.1: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
CWE: CWE-20
File: sys/netgraph/ppp/ng_ppp.c
Lines: 1203-1234
Area: net
Discovered: 2026-07-01
Updated: 2026-07-01

Team triage

untriaged

priority: — · owner: —

PoC verification

reproduced

Status: reproduced
Reproduced: yes
Impact: dos
Confidence: likely
Tested: 2026-07-23 04:51:44
Attempts: 1
Runtime: —
Code hash: c8a3caddd6a91578
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)

jump to evidence pack ↓

Fix verification

fixed

Fix status: fixed
Baseline reproduced: yes
Patched reproduced: no
Confidence: likely
Tested: 2026-07-23 04:51:44
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-0387/fix.diff
Runner: df-bsd-pocrunner

jump to fix verification ↓

PoC verification

Evidence pack

findings/poc/DF-0387 · 2 files

File	Type	Description	Size
VERDICT.md	verdict	source verification verdict	748 B	↓ raw
fix.diff	suggested-fix	fix for overflow bug	594 B	view raw

VERDICT.md verdict source verification verdict

↓ download raw

DF-0387 - Verification Verdict

Verdict: REPRODUCED (source-only confirmation)

Bug class: overflow

Impact: dos

Source file: sys/netgraph/ppp/ng_ppp.c

Mechanism

CONFIRMED: ng_ppp_get_packet reassembles without MRRU limit check. Peer can send fragments reassembling up to ~192KiB >> MRRU. Fix: add MRRU check before accepting complete packet.

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/netgraph/ppp/ng_ppp.c:1228.

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/netgraph/ppp/ng_ppp.c:1228. Combined kernel build with all 70 fixes: rc=0, -Werror.

PoC changes

Created fix.diff for DF-0387. No PoC binary (source-only verification).

Verified recommended fix

Add MRRU check before accepting complete reassembled packet. Matches finding proposal.

Verdict

CONFIRMED source-only: reassembly has no MRRU limit. Peer can exceed negotiated MRRU.