CVE-2026-99016: Linux kernel · riscv: futex: untag the user pointer before the atomic access
Source GCVE Database
Not known to be exploited · CVSS 7.8 High · fixed in 405290be962b32eec842776fbe3bdf81f15b1676 : patch Linux kernel soon.
Data as of 26 Oct 2026, 14:05 UTC
- EPSS
- 0.1% chance of exploitation in 30 days – higher than 6% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
- Patch
- Available – fixed in 405290be962b32eec842776fbe3bdf81f15b1676, 8e48d8d51ab37b7decfbff3e2844e027a52ad6ea, 2e5c80bbc062a8dda33e687ebf7be8f074ee4f7d
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:HExploitation evidence
Disclosed: evidence found.
CVE published 23 Oct 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.
What to do
Upgrade Linux kernel to 405290be962b32eec842776fbe3bdf81f15b1676, 8e48d8d51ab37b7decfbff3e2844e027a52ad6ea or 2e5c80bbc062a8dda33e687ebf7be8f074ee4f7d.
Affected software
| Product | Affected | Fixed in |
|---|---|---|
| LinuxLinux | Affected
| Fixed in
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| LinuxLinux | Affected
| Fixed in
|
| LinuxLinux | Affected
| Fixed in
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| LinuxLinux | Affected
| Fixed in– |
Description
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.
References
- nvd.nist.gov/vuln/detail/CVE-2026-99016 (opens in a new tab)
- git.kernel.org/stable/c/2e5c80bbc062a8dda33e687ebf7be8f074ee4f7d (opens in a new tab)
- git.kernel.org/stable/c/405290be962b32eec842776fbe3bdf81f15b1676 (opens in a new tab)
- git.kernel.org/stable/c/8e48d8d51ab37b7decfbff3e2844e027a52ad6ea (opens in a new tab)