# CVE-2026-98036: bpf: Preserve special fields in recycled rhtab elements

> A use-after-free in the Linux kernel BPF subsystem allows local attackers to execute arbitrary code or escalate privileges via recycled hash table elements.

- **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:** 25 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** DEBIAN-CVE-2026-98036, GHSA-3w55-5pcm-xp58, UBUNTU-CVE-2026-98036

## What is CVE-2026-98036?

CVE-2026-98036 is an use after free vulnerability in Linux, published on 25 Sep 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:

bpf: Preserve special fields in recycled rhtab elements

rhtab_map_update_elem() initializes special fields after obtaining an
element from bpf_mem_cache_alloc(). The allocator can return a fresh,
zeroed unit, or recycle one from its RCU-pending lists before the
registered destructor has run.

A BPF program can retain a map-value pointer after deleting its element
and initialize and arm a timer through that pointer. If the deleted unit
is recycled, check_and_init_map_value() clears the only pointer to the
timer. Neither a later deletion nor rhtab_mem_dtor() can then cancel it,
and the callback can run with its key and value pointing into freed memory.

Do not reinitialize special fields on insertion. Fresh allocator units are
already zeroed. For recycled units, the special fields are ownership state
that must remain visible to the eventual destructor. copy_map_value()
already skips those fields, matching the non-preallocated hash-map path and
the lifecycle established by commit 275c30bcee66 ("bpf: Don't reinit map
value in prealloc_lru_pop").

[ kkd: Split out the fix and rewrote the commit log ]

## Which versions are affected by CVE-2026-98036?


## How do I fix CVE-2026-98036?

Apply the vendor's patch.

## Is CVE-2026-98036 being exploited?

There is no known exploitation of CVE-2026-98036 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98036 and fix it if it is affected.

What it is: CVE-2026-98036 is an use after free vulnerability in Linux, published on 25 Sep 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-2026-98036 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-2026-98036/ (Markdown: https://insights.sbomify.com/CVE-2026-98036/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98036
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98036
- OSV: https://osv.dev/vulnerability/CVE-2026-98036

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98036/
Summaries are generated and may contain mistakes; the official description above is the record.