CVE-2026-31521 module: Fix kernel panic when a symbol st_shndx is out of bounds

What is CVE-2026-31521?

CVE-2026-31521 is a medium-severity vulnerability in Linux kernel, published on 22 Apr 2026. It can only be exploited from the same machine or local network, with no action from the victim.

Official description

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/[email protected]/

Weakness: CWE-787

Which versions are affected by CVE-2026-31521?

It affects 1 product.

Products include Linux kernel.

How do I fix CVE-2026-31521?

Apply the vendor's patch.

Is CVE-2026-31521 being exploited?

There is no known exploitation of CVE-2026-31521 in the wild and no public exploit code.

Other vulnerabilities in Linux kernel

• CVE-2026-53266 Linux Kernel Out-of-Bounds Write Exploited High 8.8
• CVE-2013-6282 Linux Kernel Improper Input Validation Exploited High 8.8
• CVE-2022-0185 Linux Kernel Heap-Based Buffer Overflow Exploited High 8.4
• CVE-2013-2094 Linux Kernel Privilege Escalation Exploited High 8.4
• CVE-2026-53362 Linux Kernel Unspecified Exploited High 7.8

All Linux kernel vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as AZL-83384, BELL-CVE-2026-31521, DEBIAN-CVE-2026-31521, GHSA-h7p4-fpxw-m265, ROOT-OS-DEBIAN-11-CVE-2026-31521, ROOT-OS-DEBIAN-12-CVE-2026-31521 and 4 more.