Live › vulnerability › CVE-2026-99016
Go to dashboardOn RISC-V kernels with tagged address support, the futex helpers perform atomic operations on a raw tagged user pointer instead of the untagged address that passed the access check. A local unprivileged process can make FUTEX_WAKE_OP perform read-modify-write operations on an arbitrary kernel address and read results through the comparison outcome.
Summary written from the sources below. Check the originals before acting.
First seen by InfraStack 2026-10-23 21:57 UTC. All times on this page are UTC.
Only RISC-V systems with the tagged address ABI enabled (CONFIG_RISCV_ISA_SUPM and PR_SET_TAGGED_ADDR_CTRL with PMLEN set) and Sv57 paging are described as exposed. Any local user on such a machine can trigger it, so shared multi-user hosts matter most. Systems on other architectures are not described as affected.
No product ranges from the sources yet.
uname -r and whether the machine is RISC-V with uname -m.grep CONFIG_RISCV_ISA_SUPM /boot/config-$(uname -r).uname -r.Each row is the first time that source carried this signal. The analyst’s rows are its own findings.
In the Linux kernel, the following vulnerability has been resolved:
riscv: futex: untag the user pointer before the atomic access
access_ok() checks untagged_addr(uaddr), but arch_futex_atomic_op_inuser() and futex_atomic_cmpxchg_inatomic() hand the raw uaddr to the inline asm amoswap/amoadd/.../lr.w+sc.w through the "+m" (*uaddr) operand. When the tagged address ABI is enabled (CONFIG_RISCV_ISA_SUPM, prctl PR_SET_TAGGED_ADDR_CTRL with PMLEN != 0), those two addresses differ: a user pointer whose top PMLEN bits hold a tag passes access_ok() after untagging, but the atomic is then performed on the still-tagged raw address.
Supervisor-mode data accesses are not subject to the U-mode pointer masking (that is governed by menvcfg.PMM, which the kernel does not set), so hardware does not strip the tag for the kernel's own access. With Sv57 and PMLEN=16 the tag bits overlap the canonical-address bits, so a tagged pointer can name a canonical kernel virtual address (e.g. in the linear map) whose untagged form is a valid user address. An unprivileged process can thus make FUTEX_WAKE_OP perform an atomic read-modify-write on an arbitrary kernel address, with the matching FUTEX_OP_CMP_* result serving as a read oracle.
get_user()/put_user()/raw_copy_{to,from}_user() already untag the pointer after the access_ok() check; do the same in the futex helpers so the atomic operates on the address that was actually validated.
This page as .md · .json · in your agent: get_signal("CVE-2026-99016")
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