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CVE-2026-93138
bpf: Fix vmlinux BTF prep race in bpf_get_btf_vmlinux
Published 2026-09-17 (31 days ago) by the Linux kernel CNA. Subsystem kernel/bpf. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-93138 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | fixedDLA-4841-1 · 2026-10-17 · text | 6.1.190-1 | Update the kernel and reboot. DLA-4841-1 shipped the fix on 2026-10-17, in 6.1.190-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixedDSA-6528-1 · 2026-09-29 · text | 6.12.111-1 | Update the kernel and reboot. DSA-6528-1 shipped the fix on 2026-09-29, in 6.12.111-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.2.6-1 | Update the kernel and reboot. Fixed in 7.2.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.2.6-1 | Update the kernel and reboot. Fixed in 7.2.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4817-1 · 2026-10-04 · text | 6.12.111-1~deb12u1 | Update the kernel and reboot. DLA-4817-1 shipped the fix on 2026-10-04, in 6.12.111-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
bpf_get_btf_vmlinux() lazily parses the vmlinux BTF under the bpf_verifier_lock, but publishes the result through a plain store and re-checks it through a plain lockless load. Nothing orders the stores initializing the struct btf inside btf_parse_vmlinux() against the store publishing the pointer: On a weakly ordered arch, a concurrent first-time caller taking the lockless fast path could in principle observe the pointer before the parsed contents are visible. The mutex_unlock() does not help such a reader given it only synchronizes with a later acquisition of the same lock. Thus, publish the pointer with smp_store_release() and read it on the fast path with smp_load_acquire(). Acquire semantics are needed rather than a dependency-ordered READ_ONCE(): btf_parse_vmlinux() also populates globals outside the returned object (e.g. bpf_ctx_convert.t). An address dependency would only order accesses performed through the pointer and not cover other globals.
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/verifier.c
- What this is
- BPF [CORE]MAINTAINERS section matched on kernel/bpf/verifier.c · bpf@vger.kernel.org · Maintained
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, sid, bookworm · linux-6.12y
- 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
- 2026-09-17 (31 days ago)source
- CVSS
- 7.8 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.18%, higher than 6.7% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- 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 |
|---|---|---|
| 5.5 | 5.10.270 | f32a4a40bc63 |
| 5.5 | 5.15.221 | a7fe72d78012 |
| 5.5 | 6.1.188 | e18a10b39c99 |
| 5.5 | 6.6.157 | 978524ecfc1c |
| 5.5 | 6.12.110 | eaf302628a78 |
| 5.5 | 6.18.52 | 2892f3f44bf8 |
| 5.5 | 7.2.6 | 86d11c594d60 |
| 5.5 | 7.3 | 92863e678070 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4841-1 | 2026-10-17 | bookworm 6.1.190-1 | tracker |
| DLA-4817-1 | 2026-10-04 | bookworm 6.12.111-1~deb12u1 | tracker |
| DSA-6528-1 | 2026-09-29 | trixie 6.12.111-1 | tracker |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:LAttack vector, local
- The race is reached from local bpf(2) BPF_PROG_LOAD: bpf_prog_load() calls bpf_get_btf_vmlinux() on the attach_btf_id path, and bpf_check() always calls it before verification. No remote protocol message carries the data that publishes btf_vmlinux.
- AC:LAttack complexity, low
- The attacker issues concurrent BPF_PROG_LOAD (or BPF_MAP_CREATE of BPF_MAP_TYPE_STRUCT_OPS into bpf_struct_ops_map_alloc) so one thread runs btf_parse_vmlinux() under bpf_verifier_lock while the other takes the lockless `if (!btf_vmlinux)` load; they control both sides of that publication window.
- PR:LPrivileges required, low
- The lockless consumer is bpf_check() when bpf_token_capable(token, CAP_BPF) sets is_priv and skips mutex_lock(&bpf_verifier_lock). CAP_BPF is delegable with a BPF token into a non-init user namespace, so init-namespace root is not required.
- UI:NUser interaction, none
- The attacker issues the concurrent bpf(BPF_PROG_LOAD) or bpf(BPF_MAP_CREATE) syscalls themselves; no other user must mount a filesystem, open a file, or load a program.
- S:UScope, unchanged
- A torn struct btf and bpf_ctx_convert.t are consumed by the host verifier and BTF helpers in the same kernel; that is in-kernel privilege escalation or DoS, not a KVM/Xen guest-to-host escape or IOMMU bypass.
- C:HConfidentiality impact, high
- A lockless reader can observe btf_vmlinux before btf->types, btf->strings and btf->hdr.str_len are visible. btf_type_by_id() then returns btf->types[id] and btf_str_by_offset() returns &btf->strings[offset] (check_ptr_to_map_access, btf_find_by_name_kind), an unbounded kernel read.
- I:HIntegrity impact, high
- Privileged bpf_check() trusts that torn vmlinux BTF for PTR_TO_BTF_ID sizes, and get_kern_ctx_btf_id() walks bpf_ctx_convert.t members; garbage type metadata can accept illegal kernel stores. btf_get/btf_put on a not-yet-visible refcnt can also call_rcu btf_free_rcu of the live object.
- A:HAvailability impact, high
- get_kern_ctx_btf_id() does btf_type_member(bpf_ctx_convert.t) with no NULL check when that global is still unseen, and check_ptr_to_map_access() loads t->name_off after btf_type_by_id() returns NULL because nr_types is still 0, oopsing the kernel.