DF-0486

syncache_insert dereferences possibly-uninitialized sc2 in cache-overflow path when cachelimit=0

Summary

sc2 declared without init(:359). Cache-full branch(:377-393) searches timer queues SYNCACHE_MAXREXMTS down for non-empty, assigns sc2 only if found(:384-388). If loop completes empty -> falls through to if(sc2->sc_tp!=NULL)(:389) read of uninit ptr then syncache_drop(sc2,NULL)(:391). Unreachable in default op (cache_count>=cache_limit>0 implies entry exists). BUT boot tunable net.inet.tcp.syncache.cachelimit=0(:340-341) makes cache_count(0)>=cache_limit(0) TRUE on first SYN, all timerq empty, sc2 uninit -> panic on first remote SYN. Fix: init sc2=NULL, add null check.

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Severity: Low
Status: new
Bucket: Kernel memory corruption (UAF / OOB write)
Confidence: likely
Pass: 1 · GLM 5.2 first pass
CVSS 3.1: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U:C:N/I:N/A:H
CWE: CWE-824
File: sys/netinet/tcp_syncache.c
Lines: 359-393
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 04:51:49
Attempts: 1
Runtime: —
Code hash: c328c6524a03f538
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 04:51:50
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-0486/fix.diff
Runner: df-bsd-pocrunner

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PoC verification

Evidence pack

findings/poc/DF-0486 · 2 files

File	Type	Description	Size
VERDICT.md	verdict	source verification verdict	718 B	↓ raw
fix.diff	suggested-fix	fix for uninit bug	394 B	view raw

VERDICT.md verdict source verification verdict

↓ download raw

DF-0486 - Verification Verdict

Verdict: REPRODUCED (source-only confirmation)

Bug class: uninit

Impact: dos

Source file: sys/netinet/tcp_syncache.c

Mechanism

CONFIRMED: sc2 declared without init. Cache-full branch assigns sc2 only if loop finds non-empty queue. If empty, reads uninit ptr. Fix: init sc2=NULL.

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/netinet/tcp_syncache.c:359.

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/netinet/tcp_syncache.c:359. Combined kernel build with all 70 fixes: rc=0, -Werror.

PoC changes

Created fix.diff for DF-0486. No PoC binary (source-only verification).

Verified recommended fix

Initialize sc2=NULL. Matches finding proposal.

Verdict

CONFIRMED source-only: sc2 not initialized. Cache-full branch reads uninit if loop empty.