# CVE-2026-98813: bpf: Hold map BTF for the memory allocator destructor record

> A use-after-free in the Linux kernel BPF memory allocator allows local attackers to execute arbitrary code or escalate privileges.

- **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:** 18 Oct 2026
- **Updated:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-98813, DEBIAN-CVE-2026-98813, GHSA-8234-qcrx-h2v8, UBUNTU-CVE-2026-98813

## What is CVE-2026-98813?

CVE-2026-98813 is an use after free vulnerability in Linux, published on 18 Oct 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: Hold map BTF for the memory allocator destructor record

bpf_ma_set_dtor() duplicates map->record so that the bpf_mem_alloc
destructor can release the special fields of hash and rhash map elements
once the allocator frees them for good. btf_record_dup() only acquires
references on kernel and module BTF. Fields whose types live in the map
BTF keep pointing into it: a kptr to a local type refers to map->btf,
and a list_head or rb_root field carries a value_rec owned by the struct
meta table of map->btf.

That borrowed state can outlive the map. When RCU callbacks are still in
flight, bpf_mem_alloc_destroy() copies the allocator and defers the final
drain, together with the destructor context, to a workqueue.
bpf_map_free() then frees map->record and drops the map's BTF reference
as soon as map_free() returns. Once the program that loaded the BTF is
gone as well, the BTF is freed while the worker still uses the
duplicate. The worker dereferences it through btf_is_kernel() and
btf_find_struct_meta() in bpf_obj_free_fields() when destroying elements
that were freed under RCU, and through btf_is_kernel() in
btf_record_free() when releasing the context itself:

  BUG: KASAN: slab-use-after-free in btf_is_kernel+0x19/0x30
  Read of size 1 at addr ffff88811505dce8 by task kworker/u16:2/50
  Workqueue: events_unbound free_mem_alloc_deferred
  Call Trace:
   btf_is_kernel+0x19/0x30
   btf_record_free+0xc7/0xf0
   htab_dtor_ctx_free+0x1a/0x30
   free_mem_alloc_no_barrier+0x39/0x230
   free_mem_alloc_deferred+0x2a/0x40
   process_scheduled_works+0x5ce/0x9d0
   worker_thread+0x42a/0x5e0
   kthread+0x1f5/0x230
   ret_from_fork+0x1dd/0x390
   ret_from_fork_asm+0x1a/0x30

  Allocated by task 358:
   __kmalloc_cache_noprof+0x287/0x510
   btf_new_fd+0xf7/0x3d0
   __sys_bpf+0x487/0x840

  Freed by task 0:
   kfree+0x186/0x560
   rcu_core+0x6f6/0xd40

Freeing a map that still holds more elements than the allocator's high
watermark is enough to get there, because the bulk free during teardown
queues the RCU callback that makes bpf_mem_alloc_destroy() defer.
Non-preallocated hash maps and resizable hash maps both register the
destructor and are affected alike.

Keep one reference on the map BTF in the destructor context. Every
non-kernel pointer in the duplicated record is either map->btf or memory
owned by it, so a single reference covers kptrs, list heads, and rb
roots, and mirrors what bpf_map_meta_alloc() does for the duplicated
record of an inner map. Release it only after the duplicated record has
been freed: the worker is preemptible and not in an RCU read-side
critical section, so dropping the last reference first would let the
BTF be freed while btf_record_free() still reads its fields.

## Which versions are affected by CVE-2026-98813?


## How do I fix CVE-2026-98813?

Apply the vendor's patch.

## Is CVE-2026-98813 being exploited?

There is no known exploitation of CVE-2026-98813 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98813 and fix it if it is affected.

What it is: CVE-2026-98813 is an use after free vulnerability in Linux, published on 18 Oct 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-2026-98813 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-2026-98813/ (Markdown: https://insights.sbomify.com/CVE-2026-98813/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98813
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98813
- OSV: https://osv.dev/vulnerability/CVE-2026-98813

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98813/
Summaries are generated and may contain mistakes; the official description above is the record.