Summary
In the Linux kernel, the following vulnerability has been resolved: net: tun: Update napi->skb...
In the Linux kernel, the following vulnerability has been resolved:
net: tun: Update napi->skb after XDP process
The syzbot report a UAF issue:
BUG: KASAN: slab-use-after-free in skb_reset_mac_header include/linux/skbuff.h:3150 [inline]
BUG: KASAN: slab-use-after-free in napi_frags_skb net/core/gro.c:723 [inline]
BUG: KASAN: slab-use-after-free in napi_gro_frags+0x6e/0x1030 net/core/gro.c:758
Read of size 8 at addr ffff88802ef22c18 by task syz.0.17/6079
CPU: 0 UID: 0 PID: 6079 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full)
Call Trace:
dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
print_address_description mm/kasan/report.c:378 [inline]
print_report+0xca/0x240 mm/kasan/report.c:482
kasan_report+0x118/0x150 mm/kasan/report.c:595
skb_reset_mac_header include/linux/skbuff.h:3150 [inline]
napi_frags_skb net/core/gro.c:723 [inline]
napi_gro_frags+0x6e/0x1030 net/core/gro.c:758
tun_get_user+0x28cb/0x3e20 drivers/net/tun.c:1920
tun_chr_write_iter+0x113/0x200 drivers/net/tun.c:1996
new_sync_write fs/read_write.c:593 [inline]
vfs_write+0x5c9/0xb30 fs/read_write.c:686
ksys_write+0x145/0x250 fs/read_write.c:738
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
Allocated by task 6079:
kasan_save_stack mm/kasan/common.c:47 [inline]
kasan_save_track+0x3e/0x80 mm/kasan/common.c:68
unpoison_slab_object mm/kasan/common.c:330 [inline]
__kasan_mempool_unpoison_object+0xa0/0x170 mm/kasan/common.c:558
kasan_mempool_unpoison_object include/linux/kasan.h:388 [inline]
napi_skb_cache_get+0x37b/0x6d0 net/core/skbuff.c:295
__alloc_skb+0x11e/0x2d0 net/core/skbuff.c:657
napi_alloc_skb+0x84/0x7d0 net/core/skbuff.c:811
napi_get_frags+0x69/0x140 net/core/gro.c:673
tun_napi_alloc_frags drivers/net/tun.c:1404 [inline]
tun_get_user+0x77c/0x3e20 drivers/net/tun.c:1784
tun_chr_write_iter+0x113/0x200 drivers/net/tun.c:1996
new_sync_write fs/read_write.c:593 [inline]
vfs_write+0x5c9/0xb30 fs/read_write.c:686
ksys_write+0x145/0x250 fs/read_write.c:738
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
Freed by task 6079:
kasan_save_stack mm/kasan/common.c:47 [inline]
kasan_save_track+0x3e/0x80 mm/kasan/common.c:68
kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:576
poison_slab_object mm/kasan/common.c:243 [inline]
__kasan_slab_free+0x5b/0x80 mm/kasan/common.c:275
kasan_slab_free include/linux/kasan.h:233 [inline]
slab_free_hook mm/slub.c:2422 [inline]
slab_free mm/slub.c:4695 [inline]
kmem_cache_free+0x18f/0x400 mm/slub.c:4797
skb_pp_cow_data+0xdd8/0x13e0 net/core/skbuff.c:969
netif_skb_check_for_xdp net/core/dev.c:5390 [inline]
netif_receive_generic_xdp net/core/dev.c:5431 [inline]
do_xdp_generic+0x699/0x11a0 net/core/dev.c:5499
tun_get_user+0x2523/0x3e20 drivers/net/tun.c:1872
tun_chr_write_iter+0x113/0x200 drivers/net/tun.c:1996
new_sync_write fs/read_write.c:593 [inline]
vfs_write+0x5c9/0xb30 fs/read_write.c:686
ksys_write+0x145/0x250 fs/read_write.c:738
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
After commit e6d5dbdd20aa ("xdp: add multi-buff support for xdp running in
generic mode"), the original skb may be freed in skb_pp_cow_data() when
XDP program was attached, which was allocated in tun_napi_alloc_frags().
However, the napi->skb still point to the original skb, update it after
XDP process.
Impact
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2025-39984? CVE-2025-39984 is a unknown-severity security vulnerability. No fixed version is listed yet.
- Is there a fix for CVE-2025-39984? No fixed version is listed for CVE-2025-39984 yet. Monitor the advisory for updates and apply mitigations in the interim.
- Is CVE-2025-39984 exploitable, and should I be worried? Whether CVE-2025-39984 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2025-39984 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.