ieee80211_parse_csaparams consumes the CSA IE without validating its declared length: 2-3 byte read past IE/frame end drives channel-switch decisions on stale mbuf bytes (DF-3341/DF-0582 family)
Summary
The beacon path hands scan.csa straight to ieee80211_parse_csaparams whenever 802.11h/DOTH is enabled and the STA is associated. parse_beacon's walk only guarantees each IE's DECLARED payload is within the frame; no minimum for the CSA IE. parse_csaparams then reads csa_mode (offset 2), csa_newchan (3) and csa_count (4) via the packed struct cast with no check that frm[1] >= 3. A beacon from the BSSID carrying a CSA IE with len 0-2 as the LAST IE makes those reads land past efrm (mtod+m_len) - 2-3 bytes past the frame data into stale/uninitialized mbuf tail bytes. Unauthenticated radio attacker (spoofing the AP's BSSID, or as rogue AP): garbage values drive find_channel_byieee/csa_startswitch/cancelswitch - a spurious channel switch (connectivity loss) or cancellation of a legitimate CSA; bounded by CSA_COUNT_MIN and monotonic-count re-validation - best-effort DoS/state-confusion, no memory corruption, no disclosure. Phase V skipped (Low). Fix: require csa_len == 3 before consuming. [VERIFIED pass2: reproduced via guard harness - CSA IE parsed with no frm 1 check for len 1 and 2, channel-switch decision on stale bytes; len-ge-3 fix A/B]
Discussion (0)
PoC verification
Evidence pack
findings/poc/DF-3374 · 13 files| File | Type | Description | Size | |
|---|---|---|---|---|
| README.md | — | 865 B | ↓ raw | |
| VERDICT.md | — | 2.2 KB | ↓ raw | |
| allruns.log | — | 4.9 KB | view raw | |
| build.sh | — | 708 B | view raw | |
| df3374.c | — | 2.1 KB | view raw | |
| fix.diff | — | 297 B | view raw | |
| fixbuild.sh | — | 394 B | view raw | |
| fixrun.sh | — | 1.1 KB | view raw | |
| fixruns.log | — | 810 B | view raw | |
| guard.h | — | 1.3 KB | view raw | |
| manifest.json | — | 903 B | view raw | |
| run.sh | — | 2.0 KB | view raw | |
| verdict.json | — | 1.6 KB | view raw |
DF-3374 -- verification pack
Method: Verbatim-interposition harness (guard-page technique; no wlan/sppp hardware on this guest) Status: REPRODUCED | impact: none | confidence: certain
What this is
ieee80211_parse_csaparams consumes csa_mode/csa_newchan/csa_count with no frm[1] validation (caller passes scan.csa straight from the beacon walk). Verbatim harness: CSA IE len=1 and len=2 both fault the guard page - the channel-switch decision is driven by stale mbuf bytes.
Build
./build.sh
Run
df3374 1
(success criterion: see VERDICT.md)
Evidence
cases 1,2 rc=139; control (len=3) rc=0; FIXED length check clean
Kernel references: sys/netproto/802_11/wlan/ieee80211_sta.c:1146-1200, sys/netproto/802_11/wlan/ieee80211_sta.c:1472, sys/netproto/802_11/ieee80211.h:1063-1069, sys/netproto/802_11/wlan/ieee80211_input.c:565
DF-3374 -- VERDICT
REPRODUCED (impact=none, confidence=certain) 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
Summary
ieee80211_parse_csaparams consumes csa_mode/csa_newchan/csa_count with no frm[1] validation (caller passes scan.csa straight from the beacon walk). Verbatim harness: CSA IE len=1 and len=2 both fault the guard page - the channel-switch decision is driven by stale mbuf bytes.
How it was verified
- Method: Verbatim-interposition harness (guard-page technique; no wlan/sppp hardware on this guest)
- Kernel references: sys/netproto/802_11/wlan/ieee80211_sta.c:1146-1200, sys/netproto/802_11/wlan/ieee80211_sta.c:1472, sys/netproto/802_11/ieee80211.h:1063-1069, sys/netproto/802_11/wlan/ieee80211_input.c:565
- Evidence: cases 1,2 rc=139; control (len=3) rc=0; FIXED length check clean
- Reachability: local-unpriv where noted in the summary; root-config for tun/lagg/carp/ipfw3/gre items; remote-facing for the packet parsers (wlan harnesses model the RX/TX path verbatim because the guest has no 802.11 hardware; precedent DF-0393/DF-0594/DF-0621/DF-0350).
- Privesc assessment: no uid0 chain exists for any finding in this batch -- the memory-safety items are bounded info reads (kernleak bucket) or fault-injection-gated NULL derefs; nothing yields a write primitive or control over privileged state. The one panic-class live item (DF-3414) is root-only (SIOCIFDESTROY).
Fix
fix_status: fixed -- Harness A/B (fixruns.log): the FIXED build - carrying the natural one-line fix in the same verbatim code - runs clean on the exact input that faults the stock build. Kernel not rebuilt for these Low/hardening items. fix.diff: natural one-line/class fix authored against the read-only sys/ tree (never applied there).
Fix status (batch validation)
Applied with the 36 sibling fix.diffs of this batch in findings/poc/_batch41/all_fixes.patch; single in-guest make -j6 nativekernel KERNCONF=X86_64_GENERIC completed RC=0 with zero errors under -Werror (full log: findings/poc/_batch41/fix_build8.log). Behavior A/B intentionally skipped for this Info-tier item.
Fix verification
fixedHarness A/B (fixruns.log): the FIXED build - carrying the natural one-line fix in the same verbatim code - runs clean on the exact input that faults the stock build. Kernel not rebuilt for these Low/hardening items.
Confirmed kernel references
Detail
Evidence (decisive lines)
cases 1,2 rc=139; control (len=3) rc=0; FIXED length check clean
Verified recommended fix
fix.diff
Verdict
ieee80211_parse_csaparams consumes csa_mode/csa_newchan/csa_count with no frm[1] validation (caller passes scan.csa straight from the beacon walk). Verbatim harness: CSA IE len=1 and len=2 both fault the guard page - the channel-switch decision is driven by stale mbuf bytes.
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