---
id: CVE-2026-31521
title: 'module: Fix kernel panic when a symbol st_shndx is out of bounds'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  module: Fix kernel panic when a symbol st_shndx is out of bounds

  The module loader doesn't check for bounds of the ELF section index in
  simplify_symbols():

         for…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <
    5d16f519b6eb1d071807e57efe0df2baa8d32ad6
  - >-
    Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <
    4bbdb0e48176fd281c2b9a211b110db6fd94e175
  - >-
    Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <
    082f15d2887329e0f43fd3727e69365f5bfe5d2c
  - >-
    Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <
    ec2b22a58073f80739013588af448ff6e2ab906f
  - >-
    Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <
    ef75dc1401d8e797ee51559a0dd0336c225e1776
  - >-
    Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <
    6ba6957c640f58dc8ef046981a045da43e47ea23
  - >-
    Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <
    f9d69d5e7bde2295eb7488a56f094ac8f5383b92
  - Linux 2.6.12
published: '2026-04-22'
updated: '2026-09-08'
sourceUpdated: '2026-09-08T08:47:38.796Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-31521'
references:
  - url: 'https://git.kernel.org/stable/c/5d16f519b6eb1d071807e57efe0df2baa8d32ad6'
  - url: 'https://git.kernel.org/stable/c/4bbdb0e48176fd281c2b9a211b110db6fd94e175'
  - url: 'https://git.kernel.org/stable/c/082f15d2887329e0f43fd3727e69365f5bfe5d2c'
  - url: 'https://git.kernel.org/stable/c/ec2b22a58073f80739013588af448ff6e2ab906f'
  - url: 'https://git.kernel.org/stable/c/ef75dc1401d8e797ee51559a0dd0336c225e1776'
  - url: 'https://git.kernel.org/stable/c/6ba6957c640f58dc8ef046981a045da43e47ea23'
  - url: 'https://git.kernel.org/stable/c/f9d69d5e7bde2295eb7488a56f094ac8f5383b92'
tags:
  - cve.org
epss: 0.00166
epssPercentile: 0.05204
ingestedAt: '2026-09-08T15:33:26.990Z'
---

## Overview

In the Linux kernel, the following vulnerability has been resolved:

module: Fix kernel panic when a symbol st_shndx is out of bounds

The module loader doesn't check for bounds of the ELF section index in
simplify_symbols():

       for (i = 1; i < symsec->sh_size / sizeof(Elf_Sym); i++) {
		const char *name = info->strtab + sym[i].st_name;

		switch (sym[i].st_shndx) {
		case SHN_COMMON:

		[...]

		default:
			/* Divert to percpu allocation if a percpu var. */
			if (sym[i].st_shndx == info->index.pcpu)
				secbase = (unsigned long)mod_percpu(mod);
			else
  /** HERE --> **/		secbase = info->sechdrs[sym[i].st_shndx].sh_addr;
			sym[i].st_value += secbase;
			break;
		}
	}

A symbol with an out-of-bounds st_shndx value, for example 0xffff
(known as SHN_XINDEX or SHN_HIRESERVE), may cause a kernel panic:

  BUG: unable to handle page fault for address: ...
  RIP: 0010:simplify_symbols+0x2b2/0x480
  ...
  Kernel panic - not syncing: Fatal exception

This can happen when module ELF is legitimately using SHN_XINDEX or
when it is corrupted.

Add a bounds check in simplify_symbols() to validate that st_shndx is
within the valid range before using it.

This issue was discovered due to a bug in llvm-objcopy, see relevant
discussion for details [1].

[1] https://lore.kernel.org/linux-modules/20251224005752.201911-1-ihor.solodrai@linux.dev/

## Affected

- `Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 5d16f519b6eb1d071807e57efe0df2baa8d32ad6`
- `Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 4bbdb0e48176fd281c2b9a211b110db6fd94e175`
- `Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 082f15d2887329e0f43fd3727e69365f5bfe5d2c`
- `Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < ec2b22a58073f80739013588af448ff6e2ab906f`
- `Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < ef75dc1401d8e797ee51559a0dd0336c225e1776`
- `Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 6ba6957c640f58dc8ef046981a045da43e47ea23`
- `Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < f9d69d5e7bde2295eb7488a56f094ac8f5383b92`
- `Linux 2.6.12`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.