CVE-2026-98065

What the bug is

map_check_btf() allows a key-less BTF (btf_key_type_id == 0) only for maps that have a ->map_check_btf callback, and leaves the actual decision to that callback. Hash maps used to have no ->map_check_btf, so a key-less BTF was rejected outright. That changed when htab and rhtab gained a ->map_check_btf to register a dtor - htab in commit 1df97a7453ee ("bpf: Register dtor for freeing special fields") and rhtab in commit 6905f8601298 ("bpf: Allow special fields in resizable hashtab"). Neither looks at the key, so a key-less hash map now passes map_check_btf() and gets created. Reading it back through bpffs feeds the key type_id 0 into btf_type_seq_show(); btf_type_by_id() returns the void type, kind_ops[BTF_KIND_UNKN] is NULL, and btf_type_show() dereferences it: RIP: 0010:btf_type_show+0x223/0x2e0 kernel/bpf/btf.c:8232 RSP: 0018:ffffc9000399f868 EFLAGS: 00010206 RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000000 RDX: 0000000000000005 RSI: 0000000000000000 RDI: 0000000000000028 RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000000 R10: ffffc9000399f970 R11: 0000000000000001 R12: ffffffff9b96b140 R13: ffffc9000399f8e0 R14: ffff88803d393c00 R15: 0000000000000003 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000200000000000 CR3: 000000003d213000 CR4: 0000000000352ef0 DR0: 0000000039ae8f55 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 Call Trace: <TASK> btf_type_seq_show_flags+0xca/0x120 kernel/bpf/btf.c:8250 htab_map_seq_show_elem+0x12e/0x350 kernel/bpf/hashtab.c:1669 map_seq_show+0x13d/0x1e0 kernel/bpf/inode.c:293 traverse.part.0.constprop.0+0x107/0x650 fs/seq_file.c:112 traverse fs/seq_file.c:99 [inline] seq_read_iter+0x93f/0x1270 fs/seq_file.c:196 seq_read+0x344/0x4d0 fs/seq_file.c:163 vfs_read+0x1e4/0xb40 fs/read_write.c:572 ksys_pread64 fs/read_write.c:764 [inline] __do_sys_pread64 fs/read_write.c:772 [inline] __se_sys_pread64 fs/read_write.c:769 [inline] __x64_sys_pread64+0x1eb/0x250 fs/read_write.c:769 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline] do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84 entry_SYSCALL_64_after_hwframe+0x77/0x7f Reject a key-less BTF in htab_map_check_btf() and rhtab_map_check_btf(), restoring the previous behavior.

Where it lives

The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.

kernel/bpf/hashtab.c

What this is

BPF [GENERAL] (Safe Dynamic Programs and Tools)MAINTAINERS section matched on kernel/bpf/ · bpf@vger.kernel.org · Supported

Check it on the machine

grep -wE 'CONFIG_BPF|CONFIG_BPF_SYSCALL' /boot/config-$(uname -r)

Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.

Show whether Debian builds this, per release

Debian builds this code. Every release below compiles the affected file into the kernels it ships.

• bookworm, trixie, forky, sidy

y

built into the kernel image on every flavour - only a patch removes it

Build switches

CONFIG_BPF, CONFIG_BPF_SYSCALL

Reads as

all on means the file is compiled; any one off means it is not.

From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages

Signals

Published

2026-09-25 (24 days ago)source

CVSS

no vector published, unrated

Attack vector

not published

EPSS

0.17%, higher than 5.6% of all CVEssource

CISA KEV

not listedthe KEV catalogue

Debian urgency

unimportantsource

Subsystem

kernel/bpf

Upstream fixes

The versions the CNA records as introducing and fixing this, and the commit for each. source

Introduced	Fixed in	Commit
6.12.112	6.12.112	54098e3fe34e
6.18.55	6.18.55	fa047f2a0250
7.0	7.2.7	7ca231252820
7.0	7.3	0895a0c07347