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CVE.org (no NVD analysis yet)· CNA Linux

CVE-2026-98396: powerpc: Do not restore KUAP in arch_exit_to_user_mode_prepare()

Noroxi assessment

Priority: Monitor (action score 0/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 0.19% (FIRST EPSS).
  • Fixed version: Linux Linux c2549d749539487239475fbc8c614a1f9244d655, c8e80c19c3b9c8db83a14fab00445a6064992442.
  • Mentioned 1 time in Turkish national cyber security advisories (siberguvenlik.gov.tr).

Low priority for now. Upgrade to Linux Linux c2549d749539487239475fbc8c614a1f9244d655, c8e80c19c3b9c8db83a14fab00445a6064992442 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

In the Linux kernel, the following vulnerability has been resolved: powerpc: Do not restore KUAP in arch_exit_to_user_mode_prepare() KUAP means kernel cannot touch user memory unless it explicitly is enabled. In the kernel it should stay AMR_KUAP_BLOCKED. While returning to userspace just before RFI, kernel should restore the user AMR value back. Looks like GENERIC_ENTRY might be treating arch_exit_to_user_mode_prepare() as the last architecture step before returning to userspace. commit bee25f97ad24 ("powerpc: Enable GENERIC_ENTRY feature") therefore called kuap_user_restore() from that hook. But on PowerPC that is too early. After irqentry_exit() / syscall_exit_to_user_mode() we still run platform specific exit routines. e.g. code snippets showing both exception handling and system call handling as the callers of function arch_exit_to_user_mode_prepare() which does kuap_user_restore(). The below path shows that calling kuap_user_restore() is too early when called from arch_exit_to_user_mode_prepare(). Exception handling in exceptions-64s.S ======================================= bl CFUNC(do_page_fault) ..DEFINE_INTERRUPT_HANDLER_ASYNC(do_page_fault) arch_interrupt_async_enter_prepare(regs); state = irqentry_enter(regs); instrumentation_begin(); irq_enter_rcu(); handler(regs); nap_adjust_return(regs); irq_exit_rcu(); instrumentation_end(); arch_interrupt_async_exit_prepare(regs); irqentry_exit(regs, state); <<< too early irqentry_exit_to_user_mode() __exit_to_user_mode_prepare(regs, EXIT_TO_USER_MODE_WORK_IRQ); arch_exit_to_user_mode_prepare(regs, ti_work); <<< too early b interrupt_return_srr .. bl CFUNC(interrupt_exit_user_prepare) <<< already calls kuap_user_restore prep_irq_for_enabled_exit() retry can run kernel code with IRQs on. So only when that routine is fully finished is when the user KUAP should be fully restored which interrupt_exit_user_prepare() already takes care of before returning. Similarly for system call handling in interrupt_64.S ====================================================== bl CFUNC(system_call_exception) .Lsyscall_exit: addi r4,r1,STACK_INT_FRAME_REGS li r5,0 /* !scv */ bl CFUNC(syscall_exit_prepare) .. kuap_assert_locked(); syscall_exit_to_user_mode(regs); <<< too early syscall_exit_to_user_mode_prepare(regs); <<< too early kuap_user_restore(regs); <<< already calls syscall_exit_prepare(), which can enable IRQs, replay a pending interrupt, and only then rfi. Those functions already restore KUAP immediately before rfi. Note that if we restore the user AMR too early like in the current code as shown from the code snippets above, then we get the following warning when CONFIG_PPC_KUAP_DEBUG is enabled: WARNING: arch/powerpc/include/asm/book3s/64/kup.h:293 at interrupt_exit_user_prepare+0x1a0/0x1c0 Hardware name: IBM pSeries (emulated by qemu) POWER10 (architected) TRAP: 0700 LR: c00000000000d8d4 CTR: c0000000021fe500 MSR: <SF,EE,ME,IR,DR,RI,LE> CR: 44000804 XER: 20040000 interrupt_exit_user_prepare+0x1a0/0x1c0 interrupt_return_srr_user+0x8/0x12c

—No exploit Fix available
Published
Oct 14, 2026
Updated
Oct 19, 2026
EPSS
0.1% · 9th percentile
CWE
—

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Action score

0

Monitor

Low priority for now.

CVSS
0 / 40 · —
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.1%

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Affected systems

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Versions reported by the vendor

Affected version ranges reported by the assigning authority (Linux). Independent of NVD's CPE analysis and usually ahead of it.

  • Linux Linux

    • 7.2affected
    • 02565a782c1ee7e8ada38ad24a698e01d6ea9ff8 and later · before c8e80c19c3b9c8db83a14fab00445a6064992442affected · git
    • 02565a782c1ee7e8ada38ad24a698e01d6ea9ff8 and later · before c2549d749539487239475fbc8c614a1f9244d655affected · git
    • before 7.2not affected · semver
    • 7.2.7 and later · up to and including 7.2.*not affected · semver
    • 7.3 and laternot affected · original_commit_for_fix

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Debian:14linuxbefore 7.2.7-17.2.7-1

Same product

linux: all records

Other highest-scoring records for the same primary product.

  • CVE-2026-74705udp: fix potential use-after-free in tunnel segmentation
    40Plan
  • CVE-2026-74612veth: fix skb length accounting after XDP frag adjustment
    40Plan
  • CVE-2026-74475vxlan: use neigh_ha_snapshot() in route_shortcircuit()
    40Plan

Published before and after this one in the same product

  • ← EarlierCVE-2026-98394Oct 14, 2026 · af_unix: Return immediately when manage_oob() returns NULL for 0-length buffer.
    0Monitor
  • ← EarlierCVE-2026-98395Oct 14, 2026 · powerpc/entry: Fix irq_soft_mask corruption on replayed interrupt exit
    0Monitor
  • Later →CVE-2026-98397Oct 14, 2026 · platform/x86: x86-android-tablets: hold device reference for secondary fwnode teardown
    0Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
Linux Linuxc2549d749539487239475fbc8c614a1f9244d655Vendor (CNA)
Linux Linuxc8e80c19c3b9c8db83a14fab00445a6064992442Vendor (CNA)
debian:linux7.2.7-1 · Debian:14Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

  1. Published
  2. Fix recordedsame day
  3. TodayNov 5, 2026+22 d
EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

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No commit or PR link among the references.

Credits

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Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

National notice (Türkiye Cybersecurity Directorate / USOM)

Official security notices citing this record; remediation advice is on the agency's page.

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Technical details

No CVSS vector for this record, so attack conditions can't be derived.

Weakness class (CWE)

—

Attack context

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Change log

  1. Exploit maturity— → none
  2. Fix✗ → ✓

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References

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