# CVE-2026-98042: bpf: Don't resurrect a scalar id dropped by collect_linked_regs()

> A logic error in the Linux kernel BPF verifier allows local attackers to potentially escalate privileges or execute code by exploiting register state inconsistencies.

- **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-2026-98042, GHSA-2742-pgwr-hw5x, UBUNTU-CVE-2026-98042

## What is CVE-2026-98042?

CVE-2026-98042 is a 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: Don't resurrect a scalar id dropped by collect_linked_regs()

check_cond_jmp_op() copies the compared registers into
env->{false,true}_reg{1,2} before collect_linked_regs() runs and copies
those snapshots back into both branch states afterwards.

collect_linked_regs() records at most LINKED_REGS_MAX members of a
linked registers group in the jump history and calls clear_scalar_id()
for every member that does not fit. The compared register is not exempt
from that.

As a consequence, sync_linked_regs() might adjust ranges for more
registers than bpf_bt_sync_linked_regs() can propagate precision to.

Collect the linked registers before the snapshots are taken instead.
This might lead to some unnecessary clear_scalar_id's, but from
previous testing situations with many linked registers are
extremely rare.

## Which versions are affected by CVE-2026-98042?


## How do I fix CVE-2026-98042?

Apply the vendor's patch.

## Is CVE-2026-98042 being exploited?

There is no known exploitation of CVE-2026-98042 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98042 and fix it if it is affected.

What it is: CVE-2026-98042 is a 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-2026-98042 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-2026-98042/ (Markdown: https://insights.sbomify.com/CVE-2026-98042/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98042
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98042
- OSV: https://osv.dev/vulnerability/CVE-2026-98042

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98042/
Summaries are generated and may contain mistakes; the official description above is the record.