Kernel panic from out-of-bounds ELF st_shndx in Linux kernel
CVE-2026-31521 Published on April 22, 2026
module: Fix kernel panic when a symbol st_shndx is out of bounds
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/
Products Associated with CVE-2026-31521
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Affected Versions
Linux:- Version 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and below 5d16f519b6eb1d071807e57efe0df2baa8d32ad6 is affected.
- Version 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and below 4bbdb0e48176fd281c2b9a211b110db6fd94e175 is affected.
- Version 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and below 082f15d2887329e0f43fd3727e69365f5bfe5d2c is affected.
- Version 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and below ec2b22a58073f80739013588af448ff6e2ab906f is affected.
- Version 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and below ef75dc1401d8e797ee51559a0dd0336c225e1776 is affected.
- Version 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and below 6ba6957c640f58dc8ef046981a045da43e47ea23 is affected.
- Version 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and below f9d69d5e7bde2295eb7488a56f094ac8f5383b92 is affected.
- Version 5.15.203, <= 5.15.* is unaffected.
- Version 6.1.168, <= 6.1.* is unaffected.
- Version 6.6.131, <= 6.6.* is unaffected.
- Version 6.12.80, <= 6.12.* is unaffected.
- Version 6.18.21, <= 6.18.* is unaffected.
- Version 6.19.11, <= 6.19.* is unaffected.
- Version 7.0, <= * is unaffected.