DF-0487

sc_flags assign instead of OR wipes SCF_HASH and negotiated-option flags on TF_NOOPT listener

Summary

After sc->sc_flags=SCF_HASH(:1064) and correct |= additions(SCF_TIMESTAMP:1085,SCF_WINSCALE:1097,SCF_SACK_PERMITTED:1101), code does sc->sc_flags=SCF_NOOPT(:1102-1103) and sc->sc_flags=SCF_SIGNATURE(:1112-1113) — direct assign not |=. Clears SCF_HASH which syncache_respond requires via KASSERT(:1319) + uses via m_sethash(m,sc_hashval)(:1320). DEBUG kernel panics on every SYN to TF_NOOPT listener. Production: cleared flags propagate to tcpcb in syncache_socket(:839-853) -> connection loses timestamps/win-scale/SACK. Fix: use |= not =.

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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:N/AC:L/PR:N/UI:N/S:U:C:N/I:L/A:N
CWE: CWE-782
File: sys/netinet/tcp_syncache.c
Lines: 1102-1113
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 04:51:50
Attempts: 1
Runtime: —
Code hash: 6ccf9b2f905484c3
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 04:51:50
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-0487/fix.diff
Runner: df-bsd-pocrunner

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PoC verification

Evidence pack

findings/poc/DF-0487 · 2 files

File	Type	Description	Size
VERDICT.md	verdict	source verification verdict	709 B	↓ raw
fix.diff	suggested-fix	fix for logic bug	672 B	view raw

VERDICT.md verdict source verification verdict

↓ download raw

DF-0487 - Verification Verdict

Verdict: REPRODUCED (source-only confirmation)

Bug class: logic

Impact: none

Source file: sys/netinet/tcp_syncache.c

Mechanism

CONFIRMED: sc->sc_flags=SCF_NOOPT/SCF_SIGNATURE uses = instead of |=. Clears previously set flags (SCF_HASH, SCF_TIMESTAMP, etc). Fix: use |=.

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:1102.

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:1102. Combined kernel build with all 70 fixes: rc=0, -Werror.

PoC changes

Created fix.diff for DF-0487. No PoC binary (source-only verification).

Verified recommended fix

Change = to |= for SCF_NOOPT and SCF_SIGNATURE. Matches finding proposal.

Verdict

CONFIRMED source-only: sc_flags=SCF_NOOPT/SCF_SIGNATURE uses = not |=. Clears prior flags.