# CVE-2026-98629: net/sched: cls_u32: fix manual hash table handle IDR aliasing

> A logic error in the Linux kernel's u32 classifier allows handle aliasing, potentially causing traffic misrouting or resource leaks for privileged local attackers.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **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:** AZL-108719, BELL-CVE-2026-98629, DEBIAN-CVE-2026-98629, GHSA-3xrv-9p49-wqm3, UBUNTU-CVE-2026-98629

## What is CVE-2026-98629?

CVE-2026-98629 is a 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:

net/sched: cls_u32: fix manual hash table handle IDR aliasing

A u32 hash table created with an explicit handle ('tc filter add ...
handle 801: u32 divisor N') keys its IDR entry on the raw handle, while
the destroy paths free it under handle2id(handle). The two key domains
disagree for handles in the 0x800..0xFFF htid range:
handle2id() folds them back into the auto-allocated id space (1..0x7FF).

A manual table therefore leaves its raw-keyed IDR entry unreachable on
delete (a permanent leak), and its delete can drop the idr entry of an
unrelated live auto table. A later auto allocation can then hand out a
handle that aliases the live manual table; u32_lookup_ht() first-match
routes lookups and TCA_U32_LINK for that htid to the wrong table.

Key the divisor-path alloc on handle2id(handle) so allocation and
removal share one key domain. A manual handle that maps onto an id
already in use is rejected with -ENOSPC, and auto allocation skips ids
held by live manual tables.

Conditions to recreate:
  ip link add test0 type dummy
  tc qdisc add dev test0 clsact
  tc filter add dev test0 ingress protocol ip pref 1 \
          handle 801: u32 divisor 16
  tc filter add dev test0 ingress protocol ip pref 2 u32 divisor 16
  tc -d filter show dev test0 ingress | grep 'fh 801:'
  # unpatched: two live tables with handle 0x80100000 (the pref 2 root
  # hnode is auto-allocated id 1); patched: the auto hnode takes id 2.

Also tested with a poc with a live u32 table on the block, add/delete a manual
table 'handle 901: u32 divisor 1' twice; unpatched, the re-add fails with
-ENOSPC because the raw key leaked on the first delete.

## Which versions are affected by CVE-2026-98629?


## How do I fix CVE-2026-98629?

Apply the vendor's patch.

## Is CVE-2026-98629 being exploited?

There is no known exploitation of CVE-2026-98629 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98629 and fix it if it is affected.

What it is: CVE-2026-98629 is a 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-2026-98629 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-2026-98629/ (Markdown: https://insights.sbomify.com/CVE-2026-98629/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98629
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98629
- OSV: https://osv.dev/vulnerability/CVE-2026-98629

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98629/
Summaries are generated and may contain mistakes; the official description above is the record.