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VulnerabilityPublished Updated

CVE-2026-99016: Linux kernel · riscv: futex: untag the user pointer before the atomic access

Source GCVE Database

0
Authoritative record:CVE-2026-99016· High 7.8

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

CVSS 3.1 base score
7.8High
How severe the flaw is on the 0–10 CVSS scale.
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:H

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 23 Oct 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponised: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq 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

ProductAffectedFixed in
LinuxLinuxAffected
  • ≥ 2e1743085887ba3f553c2bb472a75a3ff744b242, < 405290be962b32eec842776fbe3bdf81f15b1676
Fixed in
  • 405290be962b32eec842776fbe3bdf81f15b1676
LinuxLinuxAffected
  • ≥ 2e1743085887ba3f553c2bb472a75a3ff744b242, < 8e48d8d51ab37b7decfbff3e2844e027a52ad6ea
Fixed in
  • 8e48d8d51ab37b7decfbff3e2844e027a52ad6ea
LinuxLinuxAffected
  • ≥ 2e1743085887ba3f553c2bb472a75a3ff744b242, < 2e5c80bbc062a8dda33e687ebf7be8f074ee4f7d
Fixed in
  • 2e5c80bbc062a8dda33e687ebf7be8f074ee4f7d
LinuxLinuxAffected
  • =6.13
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

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