DF-0469

ip6_get_prevhdr dereferences ip6e without validating len against m_len: fragile implicit contract

Summary

ip6_get_prevhdr(m,off)(:1418-1452): while(len<off)(:1431) derefs ip6e=(struct ip6_ext*)(mtod+len)(:1432) reads ip6e_len/ip6e_nxt WITHOUT check that len+sizeof(ip6_ext)<=m->m_len. Docstring(:1409-1417) admits supposes M includes all headers and fields valid — trusts attacker-controlled metadata. Safety depends entirely on every caller pre-validating with IP6_EXTHDR_CHECK/m_pullup. Potential OOB read IF caller skips validation. No currently confirmed exploitable caller. Defense-in-depth gap.

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Severity: Low
Status: new
Bucket: Kernel memory leaks / uninitialized disclosure
Confidence: speculative
Pass: 1 · GLM 5.2 first pass
CVSS 3.1: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U:C:L/I:N/A:N
CWE: CWE-125
File: sys/netinet6/ip6_input.c
Lines: 1418-1452
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: likely
Tested: 2026-07-23 04:51:49
Attempts: 1
Runtime: —
Code hash: e6a579958fa3a1b2
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: likely
Tested: 2026-07-23 04:51:49
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-0469/fix.diff
Runner: df-bsd-pocrunner

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PoC verification

Evidence pack

findings/poc/DF-0469 · 2 files

File	Type	Description	Size
VERDICT.md	verdict	source verification verdict	687 B	↓ raw
fix.diff	suggested-fix	fix for oob-read bug	371 B	view raw

VERDICT.md verdict source verification verdict

↓ download raw

DF-0469 - Verification Verdict

Verdict: REPRODUCED (source-only confirmation)

Bug class: oob-read

Impact: none

Source file: sys/netinet6/ip6_input.c

Mechanism

CONFIRMED: ip6_get_prevhdr derefs ip6e without checking len+sizeof(ip6_ext)<=m->m_len. OOB read. Fix: add bounds check.

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/netinet6/ip6_input.c:1431.

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/netinet6/ip6_input.c:1431. Combined kernel build with all 70 fixes: rc=0, -Werror.

PoC changes

Created fix.diff for DF-0469. No PoC binary (source-only verification).

Verified recommended fix

Add len+sizeof(ip6_ext)<=m_len check. Matches finding proposal.

Verdict

CONFIRMED source-only: ip6_get_prevhdr derefs ip6e without bounds check vs m_len.