Unvalidated user pointers in RTIO syscall verifiers allow a user-mode thread to write kernel memory
- Exploited
- No known exploitation
- Fix
- Fixed in 4.3.2, 4.5.0
- Who is exposed
- Not reported
Do first: Upgrade to a fixed version: 4.3.2, 4.5.0.
- Exploitation?/40Exploitation: unknown (data gap). No CISA SSVC exploitation rating yet
- Exposure?/25Exposure: unknown (data gap). No advisory context yet
- Reach?/20Reach: unknown (data gap). No tracked technology or package matched
- Severity8.8/10CVSS 8.8
- No patch0/5No signal
What would change the score
- Would score about 64 if added to CISA KEV
- Would score about 59 if CISA's SSVC rates exploitation active
- Would score about 31 if advisories confirm default setups are exposed
CVE-2026-16511 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 8.8 (high) and affects zephyr; fixed in 4.3.2 and 4.5.0.
- Last modified
- Where the record stands: published, rejected by its publisher, or superseded by another id.What do these mean? →
- Published
- Whether CISA lists it in its Known Exploited Vulnerabilities catalog: proof that attackers are using it.What do these mean? →
- Not listed in CISA KEV
- FIRST's estimate of the chance attackers exploit it in the next 30 days, updated daily.What do these mean? →
- 0.17% · 6th percentile
- A 0-100 score for how much a CVE matters across the industry: exploitation, exposure, how widely the software is used, severity and whether a fix exists.What do these mean? →
- 9/100 · provisional
- Fix
- Fixed in 4.3.2, 4.5.0
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
Summary
Two RTIO syscall verifiers, in subsys/rtio/rtio_syscalls.c (subsys/rtio/rtio_handlers.c before v4.3.0), did not validate user-supplied pointers before the kernel wrote through them. z_vrfy_rtio_sqe_cancel() performed no validation at all. It passed the caller's struct rtio_sqe pointer straight to z_impl_rtio_sqe_cancel(), which converts it with CONTAINER_OF to a struct rtio_iodev_sqe, ORs RTIO_SQE_CANCELED (BIT(3)) into its 16-bit flags field in supervisor mode, then loads its next pointer and repeats until that pointer is NULL. The syscall takes no RTIO context argument, so it needs no object grant: any user-mode thread on a CONFIG_USERSPACE build can set that bit in a 16-bit word at an address of its choosing in kernel memory, and the kernel continues the write along whatever pointer chain it finds at the corresponding offset. Setting chosen bits in kernel data structures, such as object permission or thread state fields, can be used to escalate privilege from user mode. z_vrfy_rtio_sqe_copy_in_get_handles() validated its RTIO context and the input SQE array, but only NULL-checked the handle out-parameter before writing a kernel SQE pointer through it, with no K_SYSCALL_MEMORY_WRITE check. A user thread that holds a granted RTIO context can therefore make the kernel store a pointer value at an arbitrary address. The fixes validate the handle out-parameter as writable, bound the cancel handle to real submission-pool storage, and require permission on the RTIO context that owns the matching pool. Without that last check a bounded handle still let any user thread cancel submissions belonging to other contexts, silently aborting their I/O. Systems built without CONFIG_USERSPACE or without CONFIG_RTIO are unaffected.
What to do
Upgrade to a fixed version: 4.3.2, 4.5.0.
Timeline
- CVE published
- First seen by cve.now
Affected versions
- zephyr
From 3.4.0 · fixed in 4.3.2; From 4.4.0 · fixed in 4.5.0
Evidence 4
- Advisory
- Patch
- Patch
- Patch
Corrections
None so far.
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Questions about CVE-2026-16511
Is CVE-2026-16511 being exploited?
It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.Source: cve.now feed data
Which versions are affected by CVE-2026-16511?
zephyr: from 3.4.0 before 4.3.2; from 4.4.0 before 4.5.0.Source: cve.now feed data
How do I fix CVE-2026-16511?
Upgrade to a fixed version: 4.3.2, 4.5.0.Source: cve.now feed data