# CVE-2026-98525: mctp: route: iterate socket tag list in mctp_lookup_prealloc_tag()

> A local attacker can consume another socket's preallocated MCTP tag, bypassing isolation and potentially disrupting communication.

- **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:** AZL-109196, BELL-CVE-2026-98525, DEBIAN-CVE-2026-98525, GHSA-v647-mrp8-mh99, UBUNTU-CVE-2026-98525

## What is CVE-2026-98525?

CVE-2026-98525 is a missing authorization 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:

mctp: route: iterate socket tag list in mctp_lookup_prealloc_tag()

When a socket transmits a packet with MCTP_TAG_PREALLOC set,
mctp_lookup_prealloc_tag() iterates over the per-netns &mns->keys list
and matches netid, req_tag, peer_addr, and manual_alloc, without
checking whether tmp->sk == &msk->sk. This allows any MCTP socket in the
same network namespace to use and consume another socket's preallocated
tag.

Iterate the socket's own tag list (&msk->keys via sklist) instead of the
namespace-wide &mns->keys list in mctp_lookup_prealloc_tag(), ensuring
that only tags allocated by msk are matched.

Tested in QEMU against Linux 7.3.0-rc3 by allocating a manual tag
(0x18) on socket A via SIOCMCTPALLOCTAG for peer EID 9 and sending a
4-byte message with MCTP_TAG_PREALLOC from socket B in the same network
namespace. On the unfixed kernel, sendto(sock_b) using socket A's
preallocated tag succeeds (ret = 4); with this patch applied,
sendto(sock_b) fails with -ENOENT (errno = 2) while sendto(sock_a)
succeeds (ret = 4).

## Which versions are affected by CVE-2026-98525?


## How do I fix CVE-2026-98525?

Apply the vendor's patch.

## Is CVE-2026-98525 being exploited?

There is no known exploitation of CVE-2026-98525 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98525 and fix it if it is affected.

What it is: CVE-2026-98525 is a missing authorization 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-2026-98525 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-2026-98525/ (Markdown: https://insights.sbomify.com/CVE-2026-98525/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98525
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98525
- OSV: https://osv.dev/vulnerability/CVE-2026-98525

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98525/
Summaries are generated and may contain mistakes; the official description above is the record.