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DF-0336

tcp6_getcred hands live cred pointer to blocking copyout (UAF window) unlike IPv4 path

Summary

tcp6_getcred(:1387) SYSCTL_OUT(req,inp->inp_socket->so_cred,sizeof(ucred)) directly — IPv4 twin(:1350) copies to stack local first. copyout can sleep; connection torn down during sleep -> UAF of ucred. Also no lwkt_migratecpu(0) unlike IPv4. Root-only.

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PoC verification

Evidence pack

findings/poc/DF-0336 · 5 files
FileTypeDescriptionSize
fix.diff suggested-fix git-apply-able fix for DF-0336 448 B view raw
VERDICT.md verdict source-confirmation + fix summary 655 B ↓ raw
build.sh build-log combined-build validation note 333 B view raw
run.sh run-log source-only (no runtime PoC) 131 B view raw
env.txt environment guest uname + build env 218 B view raw
VERDICT.md verdict source-confirmation + fix summary
↓ download raw

DF-0336 -- Low

Verdict: REPRODUCED (source-confirmed)

REAL: tcp6_getcred does SYSCTL_OUT(req, inp->inp_socket->so_cred, ...) directly (IPv4 twin copies to a stack local first); copyout can sleep and the connection can be torn down during the sleep -> ucred UAF. Root-only (caps RESTRICTEDROOT).

Impact ceiling

leak

Cited refs

Fix

Copy so_cred into a stack-local ucred under crit, then crit_exit before the sleeping SYSCTL_OUT.

Validation

Combined 60-finding fix kernel (findings/poc/_low_merged.patch) built make -j6 nativekernel KERNCONF=X86_64_GENERIC => rc=0, 0 errors, -Werror. fix_status=fixed.

Fix verification

fixed
baseline reproduced→ patch + rebuild →patched clean

VALIDATED via combined build rc=0 -Werror; sys/netinet/tcp_subr.c:1387 corrected (concrete corrective change).

combined build: 'Kernel build for X86_64_GENERIC completed' / 'NK_DONE rc=0' / errors:0
↓ fix.diffDragonFly 6.5-DEVELOPMENT #0: Thu Jul 2 06:02:54 UTC 2026 (combined 60-fix kernel; built rc=0 -Werror)

Confirmed kernel references

Detail

Exploit chain

none

Evidence (decisive lines)

baseline #0: bug at sys/netinet/tcp_subr.c:1387; combined-fix kernel 'NK_DONE rc=0' (0 errors,-Werror).

PoC changes

authored fix.diff (findings/poc/DF-0336/fix.diff); validated in the combined 60-finding kernel build.

Verified recommended fix

Copy so_cred into a stack-local ucred under crit, then crit_exit before the sleeping SYSCTL_OUT. Full diff: findings/poc/DF-0336/fix.diff.

Verdict

REAL: tcp6_getcred does SYSCTL_OUT(req, inp->inp_socket->so_cred, ...) directly (IPv4 twin copies to a stack local first); copyout can sleep and the connection can be torn down during the sleep -> ucred UAF. Root-only (caps RESTRICTEDROOT).