# CVE-2026-72431: alloc_tag: fix use-after-free in /proc/allocinfo after module unload

> A use-after-free in the Linux kernel's allocinfo interface allows local attackers to execute code or escalate privileges after module unload.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 15 Aug 2026
- **Updated:** 17 Aug 2026
- **Also known as:** BELL-CVE-2026-72431, DEBIAN-CVE-2026-72431, GHSA-pcf6-jjpm-2jrr, UBUNTU-CVE-2026-72431

## What is CVE-2026-72431?

CVE-2026-72431 is an use after free vulnerability in Linux, published on 15 Aug 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:

alloc_tag: fix use-after-free in /proc/allocinfo after module unload

allocinfo_start() only reinitializes the codetag iterator at position 0. 
For subsequent reads (position > 0), it reuses cached iterator state from
the previous batch.  allocinfo_stop() drops mod_lock between read batches,
which allows module unload to complete and free the module memory that the
cached iterator still references:

  CPU0 (read)                        CPU1 (rmmod)
  ----                               ----
  allocinfo_start(pos=0)
    down_read(mod_lock)
    allocinfo_show()
    ...
  allocinfo_stop()
    up_read(mod_lock)
                                     codetag_unload_module()
                                       kfree(cmod)
                                       release_module_tags()
                                     ...
                                     free_mod_mem()
  allocinfo_start(pos=N)
    down_read(mod_lock)
    // reuses cached iter, skips re-init
  allocinfo_show()
    ct->filename   <-- UAF

After free_mod_mem() frees the module's .rodata, allocinfo_show()
dereferences ct->filename, ct->function which point there.

Save the iterator state in allocinfo_next() and resume from it in
allocinfo_start() with codetag_next_ct(), which detects module removal via
idr_find() returning NULL and skips to the next module.

## Which versions are affected by CVE-2026-72431?


## How do I fix CVE-2026-72431?

Apply the vendor's patch.

## Is CVE-2026-72431 being exploited?

There is no known exploitation of CVE-2026-72431 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-72431 and fix it if it is affected.

What it is: CVE-2026-72431 is an use after free vulnerability in Linux, published on 15 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-72431 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-72431/ (Markdown: https://insights.sbomify.com/CVE-2026-72431/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-72431
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-72431
- OSV: https://osv.dev/vulnerability/CVE-2026-72431

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-72431/
Summaries are generated and may contain mistakes; the official description above is the record.