CVE-2026-99018: Linux kernel · riscv: entry: gate shadow call stack reload on sstatus.SPP, not tp
Source GCVE Database
Not known to be exploited · CVSS 7.8 High · fixed in 6639735367a7d491977e9e5e7afc50b489d81d83 : patch Linux kernel soon.
Data as of 26 Oct 2026, 13:47 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 6639735367a7d491977e9e5e7afc50b489d81d83, 37b4401ee6fa06046446d55e97e8d11784080843, 7d1367a53137e379498eb8791295e58854378636 +1
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 6639735367a7d491977e9e5e7afc50b489d81d83, 37b4401ee6fa06046446d55e97e8d11784080843, 7d1367a53137e379498eb8791295e58854378636 or 4d0697f192975dab5985e921989be1d85cf580e9.
Affected software
| Product | Affected | Fixed in |
|---|---|---|
| LinuxLinux | Affected
| Fixed in
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| LinuxLinux | Affected
| Fixed in
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| LinuxLinux | Affected
| Fixed in
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| LinuxLinux | Affected
| Fixed in
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| LinuxLinux | Affected
| Fixed in– |
Description
In the Linux kernel, the following vulnerability has been resolved: riscv: entry: gate shadow call stack reload on sstatus.SPP, not tp Under CONFIG_SHADOW_CALL_STACK, handle_exception() reloads the kernel shadow call stack pointer (gp) only when the trap came from userspace. It made that decision with scs_load_current_if_task_changed, which compares the trap-time tp (read back from sscratch into s5) against the current tp: beq \prev, tp, _skip_scs scs_load_current _skip_scs: tp is a user-writable register. A user task that sets tp to the linear-map address of its own task_struct (¤t) before trapping makes the comparison succeed (can achieve by brute force with KASLR enable under our test), so the kernel skips scs_load_current and keeps running with the gp that userspace left in place. Under CONFIG_SHADOW_CALL_STACK gp is the shadow call stack pointer and load_global_pointer is a no-op, so the compiler-emitted "sd ra, -8(gp)" / "ld ra, -8(gp)" in every non-leaf function then write to, and return through, an attacker-controlled address -- an unprivileged kernel arbitrary-write and control-flow-hijack primitive. The poisoned gp is saved to task_struct.scs_sp on return, so the reload is skipped on every subsequent entry as well. Decide "came from userspace" from the hardware sstatus.SPP bit (already in s1 at this point) instead of from tp, mirroring the check that ret_from_exception already uses a few instructions later. SPP is written by hardware on trap entry and cannot be forged from U-mode. Legitimate behaviour is unchanged: user entries (SPP=0) reload the task shadow call stack, nested kernel entries (SPP=1) skip it.
References
- nvd.nist.gov/vuln/detail/CVE-2026-99018 (opens in a new tab)
- git.kernel.org/stable/c/37b4401ee6fa06046446d55e97e8d11784080843 (opens in a new tab)
- git.kernel.org/stable/c/4d0697f192975dab5985e921989be1d85cf580e9 (opens in a new tab)
- git.kernel.org/stable/c/6639735367a7d491977e9e5e7afc50b489d81d83 (opens in a new tab)
- git.kernel.org/stable/c/7d1367a53137e379498eb8791295e58854378636 (opens in a new tab)