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CVE-2026-92518
riscv, bpf: Fix kernel stack corruption in tailcall with CFI
Published 2026-09-17 (31 days ago) by the Linux kernel CNA. Subsystem arch/riscv. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-92518 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 | not affected | 6.1.190-1 | Nothing to do. bookworm never shipped the vulnerable code. |
| Debian 13trixie | vulnerable | 6.12.113-1 | No fix published anywhere yet, neither in Debian nor upstream for the series trixie tracks. Watch the Debian tracker page for this CVE. Advisories for trixie have historically landed a median of 11 days after publication. |
| 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. |
The vulnerability
What the bug is
When CONFIG_CFI_CLANG is enabled, prog->bpf_func already skips the kcfi instruction during setup. Including it again in the tailcall jump offset causes it to jump over an extra 4 bytes, skipping the stack pointer adjustment, which will result in kernel stack corruption.
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.
arch/riscv/net/bpf_jit_comp64.c
- What this is
- BPF JIT for RISC-V (64-bit)MAINTAINERS section matched on arch/riscv/net/ · bpf@vger.kernel.org · Maintained
Check it on the machine
grep -wE 'CONFIG_ARCH_RV64I|CONFIG_BPF_JIT' /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 does not build this code in 1 release. It does build it in 3 releases, so the answer depends on which release the machine runs.
- bookwormn
- trixieYnot built on amd64/amd64, amd64/cloud-amd64, amd64/rt/amd64, arm64/arm64, arm64/arm64-16k, arm64/cloud-arm64, arm64/rt/arm64, armel/rpi, armhf/armmp, armhf/armmp-lpae, armhf/rt/armmp, ppc64el/powerpc64le, ppc64el/powerpc64le-64k, s390x/s390x
- forky, sidYnot built on amd64/amd64, amd64/cloud-amd64, amd64/rt-amd64, arm64/arm64, arm64/arm64-16k, arm64/cloud-arm64, arm64/rt-arm64, armhf/armmp, armhf/armmp-lpae, loong64/loong64, ppc64el/powerpc64le, ppc64el/powerpc64le-64k, s390x/s390x
- n
- not enabled on any flavour - this release does not build the code
- Y
- built in where it is built at all; some flavours do not build it
- Build switches
- CONFIG_ARCH_RV64I, CONFIG_BPF_JIT
- 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
- 0.17%, higher than 6.3% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- arch/riscv
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.12 | 6.18.52 | 34b1bb33a025 |
| 6.12 | 7.2.6 | a6e11a81da34 |
| 6.12 | 7.3 | 52fb1756ea1d |
| 6.11.6 | 0 | 0 |
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 attacker-controlled input is a BPF program that uses bpf_tail_call, loaded via bpf(BPF_PROG_LOAD) in __sys_bpf(). emit_bpf_tail_call() then calls __build_epilogue(true), which emits the miscomputed jalr; no remote protocol carries that bytecode.
- AC:LAttack complexity, low
- On CONFIG_CFI, bpf_int_jit_compile() sets prog->bpf_func to ro_insns+cfi_get_offset() (skipping the kcfi word), while __build_epilogue() still adds RV_KCFI_NINSNS to the jalr immediate, so every tail call lands past the prologue addi-to-SP. The attacker loads the caller/callee and runs them; no race or uninfluenced layout is required.
- PR:LPrivileges required, low
- bpf_prog_load() allows BPF_PROG_TYPE_SOCKET_FILTER without CAP_BPF when unprivileged BPF is enabled, BPF_MAP_TYPE_PROG_ARRAY is created without CAP_BPF, and bpf_base_func_proto() returns bpf_tail_call_proto before the CAP_PERFMON gate. Otherwise only CAP_BPF or a delegated BPF token is required, not init-namespace root.
- UI:NUser interaction, none
- The attacker loads both programs, updates the PROG_ARRAY, and runs the caller with bpf(BPF_PROG_TEST_RUN) (sk_filter_prog_ops.test_run = bpf_prog_test_run_skb) or setsockopt(SO_ATTACH_BPF) on a socket they own. No other user must mount, open, or click.
- S:UScope, unchanged
- The skipped stack allocation corrupts the host kernel stack of the thread running the JITed image (bpf_prog_test_run_skb or sk_filter_trim_cap). That is in-kernel memory corruption on the same authority, not a KVM/Xen guest-to-host or IOMMU boundary crossing.
- C:HConfidentiality impact, high
- After the tailcall jalr skips emit_addi(SP, SP, -stack_adjust), bpf_jit_build_prologue() still does emit_addi(S5, SP, bpf_stack_adjust), so BPF_REG_FP addresses the kernel caller's frame. FP-relative LDX then reads saved return addresses and locals from that frame.
- I:HIntegrity impact, high
- The same missed SP subtract means prologue sd of RA/FP/S1–S6 and BPF STX through S5 write into the kernel frame above SP. The callee epilogue then addi SP, SP, stack_adjust and jalr RA on that smashed frame, enabling a stack pivot and control-flow hijack.
- A:HAvailability impact, high
- Returning from the tail-call target with SP still at the pre-BPF kernel SP, then adding stack_adjust in __build_epilogue(), misaligns the caller of bpf_prog_run so the kernel oopses or panics; any such crash is Availability High.